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18.16: Documented Results of Climate Change - Biology

18.16: Documented Results of Climate Change - Biology


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Learning Objectives

  • Discuss the results of climate change in our world

Scientists have geological evidence of the consequences of long-ago climate change. Modern-day phenomena such as retreating glaciers and melting polar ice cause a continual rise in sea level. Meanwhile, changes in climate can negatively affect organisms.

Geological Climate Change

Global warming has been associated with at least one planet-wide extinction event during the geological past. The Permian extinction event occurred about 251 million years ago toward the end of the roughly 50-million-year-long geological time span known as the Permian period. This geologic time period was one of the three warmest periods in Earth’s geologic history. Scientists estimate that approximately 70 percent of the terrestrial plant and animal species and 84 percent of marine species became extinct, vanishing forever near the end of the Permian period. Organisms that had adapted to wet and warm climatic conditions, such as annual rainfall of 300–400 cm (118–157 in) and 20 °C–30 °C (68 °F–86 °F) in the tropical wet forest, may not have been able to survive the Permian climate change.

Watch this NASA video to discover the mixed effects of global warming on plant growth. While scientists found that warmer temperatures in the 1980s and 1990s caused an increase in plant productivity, this advantage has since been counteracted by more frequent droughts.

Present Climate Change

A number of global events have occurred that may be attributed to climate change during our lifetimes. Glacier National Park in Montana is undergoing the retreat of many of its glaciers, a phenomenon known as glacier recession. In 1850, the area contained approximately 150 glaciers. By 2010, however, the park contained only about 24 glaciers greater than 25 acres in size. One of these glaciers is the Grinnell Glacier (Figure 1) at Mount Gould. Between 1966 and 2005, the size of Grinnell Glacier shrank by 40 percent. Similarly, the mass of the ice sheets in Greenland and the Antarctic is decreasing: Greenland lost 150–250 km3 of ice per year between 2002 and 2006. In addition, the size and thickness of the Arctic sea ice is decreasing.

This loss of ice is leading to increases in the global sea level. On average, the sea is rising at a rate of 1.8 mm per year. However, between 1993 and 2010 the rate of sea level increase ranged between 2.9 and 3.4 mm per year. A variety of factors affect the volume of water in the ocean, including the temperature of the water (the density of water is related to its temperature) and the amount of water found in rivers, lakes, glaciers, polar ice caps, and sea ice. As glaciers and polar ice caps melt, there is a significant contribution of liquid water that was previously frozen.

In addition to some abiotic conditions changing in response to climate change, many organisms are also being affected by the changes in temperature. Temperature and precipitation play key roles in determining the geographic distribution and phenology of plants and animals. (Phenology is the study of the effects of climatic conditions on the timing of periodic lifecycle events, such as flowering in plants or migration in birds.) Researchers have shown that 385 plant species in Great Britain are flowering 4.5 days sooner than was recorded earlier during the previous 40 years. In addition, insect-pollinated species were more likely to flower earlier than wind-pollinated species. The impact of changes in flowering date would be mitigated if the insect pollinators emerged earlier. This mismatched timing of plants and pollinators could result in injurious ecosystem effects because, for continued survival, insect-pollinated plants must flower when their pollinators are present.


Coevolution and the Effects of Climate Change on Interacting Species

Recent studies suggest that environmental changes may tip the balance between interacting species, leading to the extinction of one or more species. While it is recognized that evolution will play a role in determining how environmental changes directly affect species, the interactions among species force us to consider the coevolutionary responses of species to environmental changes.

Methodology/Principle Findings

We use simple models of competition, predation, and mutualism to organize and synthesize the ways coevolution modifies species interactions when climatic changes favor one species over another. In cases where species have conflicting interests (i.e., selection for increased interspecific interaction strength on one species is detrimental to the other), we show that coevolution reduces the effects of climate change, leading to smaller changes in abundances and reduced chances of extinction. Conversely, when species have nonconflicting interests (i.e., selection for increased interspecific interaction strength on one species benefits the other), coevolution increases the effects of climate change.

Conclusions/Significance

Coevolution sets up feedback loops that either dampen or amplify the effect of environmental change on species abundances depending on whether coevolution has conflicting or nonconflicting effects on species interactions. Thus, gaining a better understanding of the coevolutionary processes between interacting species is critical for understanding how communities respond to a changing climate. We suggest experimental methods to determine which types of coevolution (conflicting or nonconflicting) drive species interactions, which should lead to better understanding of the effects of coevolution on species adaptation. Conducting these experiments across environmental gradients will test our predictions of the effects of environmental change and coevolution on ecological communities.


The case for climate change realism

There is a long and infamous history of world leaders marking humanity’s “last chance” to avoid the ravages of man-made climate change.

In 1989, for instance, the director of the New York office of the U.N. Environment Program warned that rising sea levels would cause entire nations to disappear if the global-warming trend were not reversed by the year 2000. “Ecological refugees will become a major concern,” he cautioned, “and what’s worse is you may find that people can move to drier ground, but the soils and the natural resources may not support life. Africa doesn’t have to worry about land, but would you want to live in the Sahara?”

In 2007, the chairman of the Intergovernmental Panel on Climate Change (IPCC) gave the world just a few years to act: “If there’s no action before 2012, that’s too late. What we do in the next two to three years will determine our future. This is the defining moment.”

Two years later, Prince Charles warned that we had just 96 months to avert “irretrievable climate and ecosystem collapse, and all that goes with it.” “Our consumerist society comes at an enormous cost to the Earth,” professed the man with multiple palaces, fleets of automobiles, a large and permanent entourage, endless opportunities for world travel, and all the other trappings of royalty. “We must face up to the fact that the Earth cannot afford to support it.”

More recently, President Joe Biden echoed the existentialist concerns of his environmentalist predecessors in his inaugural address: “A cry for survival comes from the planet itself. A cry that can’t be any more desperate or any more clear.” This past April, while unveiling new climate-change legislation, the president reiterated the absolute imperative to act quickly and decisively to curb greenhouse-gas emissions: “We really have no choice. We have to get this done.”

Not only were many of these predictions unfounded, their tone and optics were also often ripe for ridicule. The problem, however, is that Republicans rarely go beyond dismissive mockery in responding to climate alarmists. When then-president Donald Trump insisted global warming was a “hoax” or a concept “created by and for the Chinese,” he took this dismissive attitude too far. Though he later insisted that his comments were meant as jokes, it is clear that such rhetoric is hardly a serious response to an empirical, scientific claim about potentially worrying changes in Earth’s climate.

More concerning than the lack of seriousness in these remarks is the way such rhetoric plays into the hands of climate alarmists. The truth is that the available climate science gives serious reason to doubt, and even dispute, the claims of climate catastrophists and their allies in Washington. But when the best that Republicans can muster in defense of a more nuanced, realistic approach to understanding and responding to climate change is to refer to it as a “hoax,” they empower Democrats to publicly — and, quite frankly, credibly — accuse them of “denialism,” thereby establishing themselves as the undisputed “party of science.”

A better understanding of climate science is not merely worthwhile for improving policymaking, but for improving political strategy. If Republican leaders took the time to acquaint themselves with climate science, they would find that Democrats’ apocalyptic forecasts and radical policy proposals are largely and increasingly untethered from reality. From a purely tactical perspective, Republicans interested in fighting the Green New Deal and other extremist climate policies would be wise to cease ignoring environmental science and instead become its staunchest public advocates.

Such a re-orientation would require significant changes in the way those on the right discuss climate change. But before they can even begin implementing those changes, conservatives will need to re-engage with climate science. After having been dismissive of climate alarmism for years, it’s time for conservatives to recommit themselves to understanding the scientific basics and to arguing the compelling case for climate realism.

CAUSES OF CLIMATE CHANGE

The basic theory of man-made (“anthropogenic”) climate change is straightforward and undisputed: Atmospheric concentrations of greenhouse gases, emitted in part through the burning of fossil fuels, absorb some heat that would otherwise escape from the Earth’s atmosphere into space, raising temperatures in the troposphere (the lowest atmospheric layer) and at the Earth’s surface. This warming effect is called “radiative forcing.” As greenhouse-gas concentrations rise, this warming increases too, but with diminishing impacts. In other words, the effect of an increase in greenhouse gases grows smaller as more greenhouse gas accumulates in the atmosphere.

Radiative forcing also creates a series of highly complex feedback effects in terms of ocean evaporation, cloud formation, precipitation, and other phenomena over which there exists far less scientific consensus. Because of that substantial uncertainty, the net effects of both radiative forcing and its associated feedback effects on global temperatures are the subject of sharp debate.

Despite political rhetoric suggesting the contrary, there is little dispute in the scientific literature that the amount of warming caused by radiative forcing alone is small: A doubling of atmospheric greenhouse-gas concentrations in the absence of feedback effects would increase surface temperatures by about 1 degree Celsius after the climate system fully adjusts. But that slight warming creates feedback effects that would affect the initial forcing impact. Thus, the determinative question in scientists’ attempts to predict the impact of anthropogenic climate change is how “sensitive” the Earth’s climate system is to radiative forcing. A low sensitivity would mean warming caused by man will be very small or even undetectable, while a high sensitivity would mean warming caused by man could be catastrophic.

Anthropogenic warming is “real” in the sense that increasing atmospheric concentrations of greenhouse gases are having detectable effects. The difficult issues are whether those effects are large or small, whether the resulting changes are adverse or beneficial on net (only extremists deny that there are some benefits to warming), and the degree to which natural variations are also contributing to climate change.

This last question is especially crucial in determining the scale of anthropogenic warming. After all, climate phenomena are driven by much more than atmospheric concentrations of greenhouse gases. One example among many is the Pacific Decadal Oscillation, a shift in circulation patterns in the northern Pacific Ocean that occurs approximately every 30 years. It has a warm phase and a cool phase, affecting temperatures in the northern hemisphere. Another example is the Southern Oscillation, which involves cycles of temperature fluctuation — known commonly as “El Niño” during the warm phase and “La Niña” during the cool phase — in the eastern and central equatorial Pacific Ocean. A third is the Atlantic Multi-Decadal Oscillation, a natural variability in sea-surface temperatures in the North Atlantic Ocean with cycles estimated at 60 to 80 years. There is also a substantial body of evidence indicating that changes in solar activity affect climate patterns on Earth as well. These examples are far from exhaustive.

In short, the complexity of the climate system is not to be understated. Moreover, the concept of a global surface temperature — quite apart from whether there have been changes in it — is more problematic than is commonly recognized. This figure is not the result of a single, centralized measurement instead, it is the average of large positive and negative data reported by widely dispersed measurement stations subject to often-uncorrected changes in surrounding conditions. Notwithstanding those data issues, it is useful to briefly review the available global surface (land and ocean) temperature record since the “Little Ice Age,” which ended no later than 1850.

The Earth is warming: The data reported by the National Oceanic and Atmospheric Administration (NOAA) show that temperatures increased after 1850 until the early 1880s, and then fell — particularly after the eruption of Krakatoa in 1883 — until 1910. They then increased substantially (by about 0.7 degrees Celsius) through 1945. A mild cooling period followed through the mid-1970s, after which temperatures increased through the late 1990s and early 2000s. Temperatures were more-or-less constant through about 2015, and have increased since then. Beginning in 1979, the satellite measurements for the entire troposphere show warming of about 0.17 degrees Celsius per decade, and for the troposphere over the tropics, of about 0.13 degrees Celsius per decade. These measurements are consistent with those from weather satellites, the data from which extend back to the 1950s.

The 1910-1945 warming — which was very roughly the same magnitude as that observed from the mid-1970s through about 2000 — is of particular interest in that it cannot be explained by higher greenhouse-gas concentrations, which increased from 300 parts per million to 310 parts per million over that period. This reinforces the commonsense observation that temperatures result from some combination of natural and anthropogenic influences. But the former have received far less attention than one might assume. As climatologist Roy Spencer of the University of Alabama in Huntsville and NASA notes:

Very little research has ever been funded to search for natural mechanisms of warming….it has simply been assumed that global warming is manmade. This assumption is rather easy for scientists since we do not have enough accurate global data for a long enough period of time to see whether there are natural warming mechanisms at work. The United Nation’s Intergovernmental Panel on Climate Change (IPCC) claims that the only way they can get their computerized climate models to produce the observed warming is with anthropogenic [emissions]. But they’re not going to find something if they don’t search for it. More than one scientist has asked me, “What else COULD it be?” Well, the answer to that takes a little digging.

The central point here is not that we can say for certain that climate change is driven primarily by natural phenomena acting independent of anthropogenic factors. But it is important to recognize that the assumption of many politicians, environmental groups, and no small number of scientist-activists — that humans are the single most significant cause of climate change — is simply unsupported by the available science. Such an absence of evidence cautions humility it should make Americans think twice before embracing radical solutions to a problem that we are only beginning to comprehend.

CLIMATE TRENDS

Beyond exhibiting extreme overconfidence in a cherry-picked analysis of climate-change causes, politicians and activists frequently ground their alarmism in frightening predictions about consequences that are likewise far from certain. This is not only true within the very new (and still quite unreliable) field of predictive climate science it is true even in the context of ongoing climate phenomena. Indeed, politicians and journalists frequently characterize dramatic or unusual climate phenomena as the product of anthropogenic climate change, yet there is little evidence to support those claims.

For one thing, there is no observable upward trend in the number of “hot” days between 1895 and 2017 11 of the 12 years with the highest number of such days occurred before 1960. Since 2005, NOAA has maintained the U.S. Climate Reference Network, comprising 114 meticulously maintained temperature stations spaced more or less uniformly across the lower 48 states, along with 21 stations in Alaska and two stations in Hawaii. They are placed to avoid heat-island effects and other such distortions as much as possible. The reported data show no increase in average temperatures over the available 2005-2020 period. In addition, a recent reconstruction of global temperatures over the past 1 million years — created using data from ice-sheet formations — shows that there is nothing unusual about the current warm period.

Rising sea levels are another frequently cited example of impending climate crisis. And yet sea levels have been rising since at least the mid-19th century. This rise is tied closely with the end of the Little Ice Age that occurred not long before, which led to a rise in global temperatures, some melting of sea ice, and a thermal expansion of sea water. There is some evidence showing an acceleration in sea-level rise beginning in the early 1990s: Satellite measurements of sea levels began in 1992 and show a sea-level rise of about 3.2 millimeters per year between 1993 and 2010. Before 1992, when sea levels were measured with tidal gauges, the data showed an increase of about 1.7 millimeters per year on average from 1901 to 1990.

But because the datasets are from two different sources — satellite measurements versus tidal gauges — they are not directly comparable, and therefore they cannot be interpreted as showing an acceleration in sea-level rises. Moreover, the period beginning in 1993 is short in terms of global climate phenomena. Since sea levels have risen at a constant rate, remained constant, or even fallen during similar relatively short periods, inferences drawn from them are problematic. It is of course possible there has been an acceleration in sea-level rise, but even still, it would not be clear whether such a development stemmed primarily from anthropogenic or natural causes clearly, both processes are relevant.

A study of changes in Arctic and Antarctic sea ice yields very different inferences. Since 1979, Arctic sea ice has declined relative to the 30-year average (again, the degree to which this is the result of anthropogenic factors is not known). Meanwhile, Antarctic sea ice has been growing relative to the 30-year average, and the global sea-ice total has remained roughly constant since 1979.

Extreme weather occurrences are likewise used as evidence of an ongoing climate crisis, but again, a study of the available data undercuts that assessment. U.S. tornado activity shows either no increase or a downward trend since 1954. Data on tropical storms, hurricanes, and accumulated cyclone energy (a wind-speed index measuring the overall strength of a given hurricane season) reveal little change since satellite measurements of the phenomena began in the early 1970s. The number of wildfires in the United States shows no upward trend since 1985, and global acreage burned has declined over past decades. The Palmer Drought Severity Index shows no trend since 1895. And the IPCC’s Fifth Assessment Report, published in 2014, displays substantial divergence between its discussion of the historical evidence on droughts and the projections on future droughts yielded by its climate models. Simply put, the available data do not support the ubiquitous assertions about the causal link between greenhouse-gas accumulation, temperature change, and extreme weather events and conditions.

Unable to demonstrate that observed climate trends are due to anthropogenic climate change — or even that these events are particularly unusual or concerning — climate catastrophists will often turn to dire predictions about prospective climate phenomena. The problem with such predictions is that they are almost always generated by climate models driven by highly complex sets of assumptions about which there is significant dispute. Worse, these models are notorious for failing to accurately predict already documented changes in climate. As climatologist Patrick Michaels of the Competitive Enterprise Institute notes:

During all periods from 10 years (2006-2015) to 65 (1951-2015) years in length, the observed temperature trend lies in the lower half of the collection of climate model simulations, and for several periods it lies very close (or even below) the 2.5th percentile of all the model runs. Over shorter periods, such as the last two decades, a plethora of mechanisms have been put forth to explain the observed/modeled divergence, but none do so completely and many of the explanations are inconsistent with each other.

Similarly, climatologist John Christy of the University of Alabama in Huntsville observes that almost all of the 102 climate models incorporated into the Coupled Model Intercomparison Project (CMIP) — a tracking effort conducted by the Lawrence Livermore National Laboratory — overstate past and current temperature trends by a factor of two to three, and at times even more. It seems axiomatic to say we should not rely on climate models that are unable to predict the past or the present to make predictions about the distant future.

The overall temperature trend is not the only parameter the models predict poorly. As an example, every CMIP climate model predicts that increases in atmospheric concentrations of greenhouse gas should create an enhanced heating effect in the mid-troposphere over the tropics — that is, at an altitude over the tropics of about 30,000-40,000 feet. The underlying climatology is simple: Most of the tropics is ocean, and as increases in greenhouse-gas concentrations warm the Earth slightly, there should be an increase in the evaporation of ocean water in this region. When the water vapor rises into the mid-troposphere, it condenses, releasing heat. And yet the satellites cannot find this heating effect — a reality suggesting that our understanding of climate and atmospheric phenomena is not as robust as many seem to assume.

The poor predictive record of mainstream climate models is exacerbated by the tendency of the IPCC and U.S. government agencies to assume highly unrealistic future increases in greenhouse-gas concentrations. The IPCC’s 2014 Fifth Assessment Report, for example, uses four alternative “representative concentration pathways” to outline scenarios of increased greenhouse-gas concentrations yielding anthropogenic warming. These scenarios are known as RCP2.6, RCP4.5, RCP6, and RCP8.5. Since 1950, the average annual increase in greenhouse-gas concentrations has been about 1.6 parts per million. The average annual increase from 1985 to 2019 was about 1.9 parts per million, and from 2000 to 2019, it was about 2.2 parts per million. The largest increase that occurred was about 3.4 parts per million in 2016. But the assumed average annual increases in greenhouse-gas concentrations through 2100 under the four RCPs are 1.1, 3.0, 5.5, and an astounding 11.9 parts per million, respectively.

The studies generating the most alarmist predictions are the IPCC’s Special Report on Global Warming of 1.5°C and the U.S. government’s Fourth National Climate Assessment, both of which were published in 2018. Both assume RCP8.5 as the scenario most relevant for policy planning. The average annual greenhouse-gas increase under RCP8.5 is over five times the annual average for 2000-2019 and almost four times the single biggest increase on record. Climatologist Judith Curry, formerly of the Georgia Institute of Technology, describes such a scenario as “borderline impossible.”

RCP6 is certainly more realistic. It predicts a temperature increase of 3 degrees Celsius by 2100 in the average of the CMIP models. But on average, those CMIP models overstate the documented temperature record by a factor of at least two. Ultimately, models with a poor record of successfully accounting for past data and highly unrealistic future greenhouse-gas concentrations should not be considered a reasonable basis for future policy formulation.

It is worth noting that the public discussion of the climate crisis consistently ignores the very real possibility that the small amount of warming that will likely occur might yield noteworthy benefits. The peer-reviewed literature reports that over the last 35 years, a substantial greening of a quarter to half the Earth has occurred, of which over two-thirds is due to carbon-dioxide fertilization. The peer-reviewed literature also reports that this fertilization effect has been accompanied by a sharp increase in plants’ water-use efficiency. Moreover, a well-known multinational study of the mortality effects of heat and cold finds that the latter results in far more premature deaths. Though there will likely be some negative consequences of a warming planet, these early reports remind us that there will likely be positive effects as well.

Finally, we cannot ignore the potentially adverse effects of government policies designed to fight climate change. Before we rush toward hasty assessments of a climate disaster, we need to take full stock of these potential benefits and costs.

COSTS OF COMBATING CLIMATE CHANGE

The implicit assertion of various climate proposals is that they would, upon implementation, yield significant beneficial effects. Yet curiously, their proponents almost never specify the future effects in terms of temperatures and other important climate measurements. The reality is that even policies that would most aggressively reduce greenhouse-gas emissions would likely have only very small effects on climate.

To estimate the impact of such policies, we must use a climate model. This model would make predictions about temperatures that will occur at some distant future year — say, the year 2100 — both with and without the policies under consideration. For years, the U.S. government has used the climate model developed with funding from the Environmental Protection Agency. This model suits our purposes here as well as any.

The predicted effects of the various proposals put forth may surprise many readers. Even if we were to incorporate assumptions that exaggerate the impact of reduced greenhouse-gas emissions, full implementation of the “net-zero” emissions goals of the Biden administration would reduce global temperatures by 0.17 degrees Celsius by 2100. That effect would be barely detectable given normal variation in the global temperature record. The much-discussed Green New Deal — also a net-zero proposal — would have about the same effect. The Paris agreement, if implemented immediately and enforced strictly, would have a similar impact of about 0.17 degrees Celsius. A 50% emissions cut by China would yield an impact of 0.18 degrees Celsius. A net reduction to zero greenhouse-gas emissions by all 37 member states of the Organization for Economic Cooperation and Development would increase that figure to about 0.35 degrees Celsius. An immediate global emissions cut of 75% would yield an impact of 0.54 degrees Celsius.

Despite the lackluster effects of these climate proposals, they would be exceedingly costly. Sharp reductions in greenhouse-gas emissions can be accomplished only by substituting expensive energy for cheaper energy, notwithstanding ubiquitous assertions to the contrary by proponents of climate policies. My estimate of the cost of the electricity portion of the Green New Deal alone is $500 billion per year, or about $4,000 annually per U.S. household. Setting aside the reality that such policies are not even remotely viable politically, there is serious reason to doubt such extraordinary costs are worth whatever minor reductions in temperature they might achieve.

A similar analysis can be applied to the recommendations of the IPCC’s Global Warming of 1.5°C report referenced above. Buried in its supporting documentation is a discussion of the taxes on greenhouse-gas emissions that would be needed to limit warming in this century to 1.5 degrees Celsius. In 2019 dollars, the midpoint of the range for the imagined 2030 tax level comes out to $3,213 per ton. That works out to a tax per gallon of gasoline of about $30.

The way to understand the true costs of proposed climate policies is to consider the reductions in greenhouse-gas emissions that would be needed to achieve the older, “safe” levels of emissions sought by climate activists. Under the average of the CMIP models, the temperature-reduction goal for RCP6 would be 1 degree Celsius (from 3 degrees Celsius down to a goal of 2 degrees Celsius), which would require greenhouse-gas emissions cuts almost 600% greater than those promised under the Paris accord. In the RCP8.5 scenario, the average temperature increase predicted is 4.9 degrees Celsius by 2100 a reduction of 2.9 degrees Celsius would require greenhouse-gas cuts over 1700% of those promised in the agreement.

WEIGHING THE INTERESTS OF FUTURE GENERATIONS

These figures are staggering, and utterly impossible to achieve. This forces us to recognize that any policy we implement will involve significant costs and trade-offs. Rather than determining the policy solutions for us, as some politicians pretend it can do, the available climate science demands that our leaders weigh these trade-offs in consideration of our manifold interests, commitments, and values.

One important metric to consider in navigating the fraught cost-benefit analysis of a particular course of action is the concept of a “discount rate.” When applied to proposed policies, a discount rate is a weighting of the relative values of effects experienced soon (or during the current period) and those experienced further out in time. A low discount rate means that the future is not being discounted heavily relative to the present a discount rate of zero would mean that any future period, regardless of how distant in time, has the same weight as the current one. A high discount rate means that the future is discounted more heavily relative to the present.

Any investment of scarce resources must compete, at least in principle, with alternative investments. Those alternatives, on average, can be expected to yield some economic rate of return to the economy in the aggregate, even if that expected return is difficult to measure or even to define. Accordingly, the costs and benefits of alternative investments must be compared so as to yield choices among those alternatives that produce the highest total economic return to society. Conceptually, the most straightforward way to evaluate a given investment or government policy is to apply that economic rate of return as the discount rate, and to see if the stream of costs and benefits has a “net present value” greater than zero. If so, the project is justified economically, and undertaking it will increase the aggregate value of all investments considered together.

Among the chief arguments proponents of aggressive climate policies promote is the contention that climate change is a dangerous phenomenon that will impose massive harms on future generations. Accordingly, the argument goes, a low or even zero discount rate applied to the analysis of climate policies is appropriate as a means by which the interests of future generations should be taken into account.

Yet this argument is incorrect. The central interest of future generations is a bequest from previous generations of the most valuable possible capital stock (the sum of all investments), of which environmental quality is but one important dimension among many. There are always unavoidable trade-offs among these dimensions. Maximizing that bequest for future generations requires the current generation to allocate resources efficiently. If environmental policies implemented by the current generation yield less wealth currently as well as a smaller total capital stock for future generations — defined broadly to include environmental values — then, from the viewpoint of those future generations, some additional emissions of pollutants and greenhouse gas would be preferable.

Analytically speaking, climate policy is a forced investment of scarce resources in a particular set of activities and a forced disinvestment in others — for example, in the exploration and development of fossil fuels. The use of an artificially low discount rate for the valuation of those investments distorts the allocation of capital among alternative investments in the current period as well as across current and future periods. The inexorable result is a smaller capital stock to be bequeathed to future generations. An artificially low discount rate for the evaluation of climate policies, therefore, is inconsistent with the interests of future generations, which will be concerned about far more than climate phenomena alone.

To think about this in more concrete terms, it helps to imagine an infant born in a cave some tens of thousands of years ago, in a world with environmental quality effectively untouched by mankind. At birth, that child would have had a life expectancy on the order of 10 years. Had it been able to choose, it would almost certainly have willingly given up some environmental quality in exchange for a longer life expectancy engendered by better housing, food, water, medical care, safety, and other advantages ad infinitum.

The general proposition is straightforward: People willingly give up some environmental quality in exchange for lives that are longer, wealthier, and healthier. Few would choose to live on a pristine desert island most would prefer closer proximity to family, employment, entertainment, and all of the other myriad beneficial dimensions of living in a world with a less-than-pristine environment. Ultimately, then, the most responsible way for policymakers to move forward on climate policy is to weigh all of their obligations to future generations against one another, rather than focusing on one to the detriment of the rest.

Moreover, future generations will be much wealthier than the current one. The IPCC itself estimates that individual incomes by the end of the century will be at least 400% greater than is the case today, and that the damage from anthropogenic climate change unmitigated by policy initiatives will be only 2.6% of global GDP by 2100. This is virtually the same as the projections generated by the mainstream models estimating the economic effects of changing climate phenomena.

ESCAPING THE NARRATIVE

In 2006, former vice president Al Gore made it clear that “unless drastic measures to reduce greenhouse gases are taken within the next 10 years, the world will reach a point of no return.” In 2011, the International Energy Agency argued that the opportunity to avoid dangerous climate change would be “lost forever” if serious actions to limit greenhouse-gas emissions were not implemented within the ensuing five years. Somehow, the fact that these deadlines have come and gone has not led to any discrediting or re-evaluation of the original claims or demands.

Luckily for us, the truth is that the ongoing crusade for major reductions in greenhouse-gas emissions — that is, large shifts away from inexpensive energy — is grounded in an alarmism entirely unsupported by the available scientific evidence. To achieve these perpetually apocalyptic conclusions, climate catastrophists have hid behind modeling results that are notoriously unreliable, climate proposals with impacts either small or ambiguous, and a growing unwillingness to engage in actual debate. Meanwhile, those deeply skeptical of the many assertions climate activists and their political allies make have been shunted aside, branded as “denialists,” and banished from polite society.

There seems to be little incentive to challenge these alarmists or their false “science versus denial” dichotomy. But the political stakes are too high for those who can see through climate extremism to dismiss such hysterics and leave the substance of alarmists’ claims unchallenged. So long as Democrats can get away with presenting theirs as the “party of science,” they will continue to operate with a significant strategic advantage when it comes to public debates on climate policies that will have profound impacts on the country for generations to come. Instead of merely dismissing the faux science that lends support to climate alarmism as a “hoax,” conservatives must do more to engage with and reclaim the growing body of scientific evidence that supports their climate-change realism.

Benjamin Zycher is a resident scholar at the American Enterprise Institute.


Warming effect of greenhouse gases has been ‘overestimated,’ now climate scientists may know why

CAMBRIDGE, Mass. — The warming effect of greenhouse gases has been overestimated, and an international team of researchers may have pinpointed the reason why.

Smoke particles preserved for hundreds of years in Antarctica are changing how climate change experts view the impact of greenhouse gases on the planet. In particular, predicting how surface temperatures on Earth respond to these gases, which trap heat from sunlight within our atmosphere, has long been a challenge. Scientists have warned of the devastating impact of even slight changes in ocean temperatures in recent years. Now, this latest discovery that reveals more about how manmade fires even before industrialization were still prominent.

“Most studies have assumed less fire took place in the pre-industrial era,” says senior author Dr Loretta Mickley, a climate scientist at Harvard, in a statement. “The ice cores suggested a much fierier past – at least in the Southern Hemisphere.”

The international team ran computer simulations of wildfires and the burning practices of indigenous people in Australian, Africa and South America.

“The computer simulations of fire show that the atmosphere of the Southern Hemisphere could have been very smoky in the century before the Industrial Revolution. Soot concentrations in the atmosphere were up to four times greater than previous studies suggested,” explains Jed Kaplan, an associate professor at the University of Hong Kong and co-author of the study. “Most of this was caused by widespread and regular burning practiced by indigenous peoples in the pre-colonial period.”

The study published in Science Advances sheds fresh light on climate change.

How fire activity from previous generations can help predict the future

Modeling suggests as land use changes reduced fire activity, emissions from industry increased. The key is significant smoke aerosols that were identified in the pre-industrial Southern Hemisphere ice core samples.

“Up till now the magnitude of past fire activity, and thus the amount of smoke in the pre-industrial atmosphere, has not been well characterized,” says first author Dr Pengfei Liu, also from Harvard. “These results have importance for understanding the evolution of climate change from the 1750s until today, and for predicting future climate.”

They could help predict how fast surface temperatures will rise in response to increases in greenhouse gases. It is the biggest uncertainty in climate change. Calculating warming and cooling effects in the atmosphere is complicated. Greenhouse gases heat the planet’s surface. Aerosol particles from volcanoes, fires and other combustion cool it by blocking sunlight or seeding cloud cover.

Understanding sensitivity to each of the effects and how they interact is critical. Most climate models rely on past levels to validate forecasts. Greenhouse gases are well-documented, but the amount of smoke aerosols was not, until now.

So the researchers looked to Antarctica, where the ice trapped particles emitted from fires in Australia, Africa and South America. They measured soot, a key component of smoke, deposited in an array of 14 cores from across the continent provided by collaborators.

“Soot deposited in glacier ice directly reflects past atmospheric concentrations,” says study co-author Dr. Joe McConnell, from the Desert Research Institute in Nevada. “Well dated ice cores provide the most reliable long term records.”

The finding was a surprise. Still, it backs other ice core records that suggest humans were damaging the atmosphere long before the Industrial Revolution. People were mining and smelting copper in South America as early as 1400 BC. The Incas introduced the smelting of silver ore, which often contains lead, in the 15th century. Air pollution took off further when the Spanish conquistadors invaded South America in the 16th century.

Greenhouse gases viewed from a new lens in the future?

Underestimating the cooling effect of smoke particles in the pre-industrial world has important implications. It suggests climate models have over-egged the impact of greenhouse gas emissions to account for the increases in surface temperatures.

“Climate scientists have known the most recent generation of climate models have been overestimating surface temperature sensitivity to greenhouse gasses,” says Liu. “But we have not known why or by how much. This research offers a possible explanation.”

Understanding the potential consequences on people are crucial in implementing strategies to reduce the future threat.

“Clearly the world is warming, but the key question is how fast will it warm as greenhouse gas emissions continue to rise,” adds Mickley. “This research allows us to refine our predictions moving forward.”


Extreme Precipitation

Trends in 1-day and multiday heavy precipitation events in the United States and other countries show a tendency toward more days with heavy precipitation totals over the 20th century (18–20). The annual number of days exceeding 50.8 mm (2 inches) and 101.6 mm (4 inches) of precipitation has increased in the United States since 1910 (8,21). Also, the frequency of 1- to 7-day precipitation totals exceeding station-specific thresholds, for 1 in 1 year and 1 in 5 year recurrences, and the upper 5 percentiles, have been increasing since the 1930s (18, 20). Increases are largest in the southern Mississippi River valley, Southwest, Midwest, and Great Lakes regions of the United States, and increases in extreme events are responsible for a disproportionate share of the observed 5 to 10% increase in total annual precipitation since the early 20th century (20).

Most countries that experienced a significant increase or decrease in monthly or seasonal precipitation also experienced a disproportionate change in the amount of precipitation falling during the heavy and extreme precipitation events (7, 22) (Fig. 1). Furthermore, in some areas there was no increase in the seasonal total, but there was still an increase in the frequency of 1-day heavy precipitation events, as in Japan (23).

Linear trends in total seasonal precipitation and frequency of heavy precipitation events for various countries (7).

Depending on the analysis technique, some researchers analyzing changes in heavy precipitation have found increases over the 20th century in Australia, except in southwestern Australia, where there has been a decrease in both rain days and heavy events (24). In the United Kingdom, heavy wintertime events have increased and heavy summertime events have decreased (25), and in the Sahel region of Nigeria and throughout all Sudano-Sahel Zone, including Abissinian Plateau, the heaviest daily precipitation amounts have decreased, coincident with an overall decrease in annual rainfall (26). Recent results show that, although the Canadian prairie has experienced increased annual rainfall and heavy precipitation over the last 40 years, this increase appears mainly due to an increase in the number of lighter (<5 mm) daily rainfall totals (27). However, others (28) examining Canadian precipitation trends for most of the 20th century find precipitation increases in southern Canada resulting from increases in all levels of precipitation intensity, and in the latter half of the century increases are greatest in intermediate and heavy events, particularly in Arctic Canada (28).


Climate change and the ocean

Climate change has serious, long-term, and far-reaching negative consequences for our ocean.

Burning fossil fuels, raising livestock, and clearing forests are just three examples of human activities that release billions of tons of CO 2 and other heat-trapping gases into our atmosphere every year, making our planet warmer. The ocean has buffered us from the worst impacts of climate change—absorbing about 25 percent of the excess CO 2 and more than 90 percent of the excess heat. But these climate services come at a significant cost for marine ecosystems and result in harmful impacts including:

  • Increasing ocean temperature: bleaches coral reefs, shifts where fish can live, and decreases ocean wildlife,
  • Ocean acidification: causes a depletion of carbonate ions, which are critical for shell-forming animals like oysters, crabs, and shrimp,
  • Decreasing oxygen: creates areas that suffocate marine animals, shrinks their habitats, and forces them to swim into places where they are more vulnerable to predators,
  • More intense tropical storms and higher sea level: puts coastal communities in harm’s way and destroys coastal wetland habitats which include mangroves and salt marshes.

These and other negative impacts are documented and summarized in the Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate — released on September 25, 2019, in Monaco . It is the first IPCC report to focus specifically on the marine realm.

In order to protect the ocean and slow the impacts of climate change, the science indicates we need to take action on two fronts:


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Introduction

The Himalayas, which represents the major parts of the Greater Hindu-Kush Himalayan mountain system, extends in an arc about 3000 kilometers in length and covers ∼750,000 km 2 of northern Pakistan, Nepal, Bhutan, and the northwestern and northeastern states of India (Fig. S1) [1]. Climatic, topographic, geological, and altitudinal variations have generated unique landscapes, ecosystems, and biota in the Himalayas. Of the 825 ecoregions in the world, 13 are represented in the Himalayas [2]. This immense biological diversity is matched by cultural and ethnic diversity. Himalayas is also the source of the 8 largest rivers of Asia and is known as “water tower of Asia” [3] the rivers and their tributaries sustain about 1.4 billion people [4]. Thus climate change in the region is a matter of global concern.

Much of the recent discussion about climate change in the Himalayas has been dominated by the extent of glacial melting [5], [6] however, glaciers have not been systematically monitored [7]. The IPCC report predicts large scale changes in temperature and precipitation over the Asian land mass [8]. Limited studies on temperature or precipitation for a few localized places show that warming in the Himalayas is 3 times greater than the global average [3]. However, changes at the regional level remain to be documented. Furthermore, the impacts of climate change on phenological patterns are not well understood due to lack of historical ground-based observations on phenology. Thus despite the fact that the Himalayas are among the regions most vulnerable to climate change [3], have unique biodiversity, and are undergoing rapid environmental change [9], there is no systematic analysis of climate change and its effects on ecosystems and biodiversity, nor on hydrology, agriculture, and livelihoods in this important and extraordinary region of the world.

We used global mean monthly surface air temperature [10], precipitation [11], and GIMMS-NDVI dataset [12] from the year 1982 to 2006 for 13 ecoregions of the Himalayas. The global mean monthly surface air temperature dataset of 0.5-degree grid is produced from ground-based weather station data collected from the Global Historical Climatology Network version 2 and the Climate Anomaly Monitoring System using interpolation methods. The quality of this dataset is found to be reasonably good in comparison with several other ground-based land surface temperature datasets, and it captures most of the common temporal-spatial features observed in climatology both at regional and global scale [10]. Similarly, we used precipitation data produced by Climate Prediction Center Merged Analysis of Precipitation (CMAP), the 2.5-degree gridded global monthly precipitation data were produced by the combination of different sources: gauge observations and estimates inferred from a variety of satellite observations [11]. The GIMMS-NDVI dataset is corrected for different sources of non-vegetation error introduced by inter-sensor calibration, orbital drift, cloud cover, solar angle differences, volcanic eruptions, and other atmospheric contaminations [12]–[13]. Long term temporal and large spatial coverage of this data make it possible to detect trends in vegetation phenology [14]–[16]. The extracted data were analyzed in a GIS framework to detect spatio-temporal changes in climate. Since changes in temperature and precipitation are directly manifested as changes in phenology of local ecosystems, we examined the impact of such changes on the onset of growing season and senescence in the 13 different ecoregions of the Himalayas. Furthermore, we correlated changes in phenological parameters with changes in climatic variables.

IPCC predicts that average annual mean temperature over the Asian land mass, including the Himalayas, will increase by about 3°C by the 2050 s and about 5°C by the 2080 s [8], [17]. Similarly, average annual precipitation in this region will increase by 10–30% by 2080 [8]. During the last few decades, the Himalayas have experienced increasing temperature [3], [18], [19]. However, data on precipitation are not consistent the precipitation has increased in some areas but decreased in other areas [3], [20]. Changes in temperature and precipitation have influenced phenology of plants [21]–[23]. Although basic research on ecological responses, including phenology, to climatic change is substantially lacking in the Himalayas, it is generally anticipated that climate change in this region may alter phenology at both individual species and community levels [3]. Our results demonstrate significant changes in temperature and precipitation of the Himalayas–greater than the upper bounds predicted by IPCC and the recent Indian assessments [24]. Furthermore, we demonstrate that landscape-level changes in the phenology of local ecosystems all across the Himalayas are well correlated with changes in climate.


Contents

The current scientific consensus is that:

  • Earth's climate has warmed significantly since the late 1800s. [a]
  • Human activities (primarily greenhouse gas emissions) are the primary cause.
  • Continuing emissions will increase the likelihood and severity of global effects.
  • People and nations can act individually and collectively to slow the pace of global warming, while also preparing for unavoidable climate change and its consequences.

Several studies of the consensus have been undertaken. [8] Among the most cited is a 2013 study of nearly 12,000 abstracts of peer-reviewed papers on climate science published since 1990, of which just over 4,000 papers expressed an opinion on the cause of recent global warming. Of these, 97% agree, explicitly or implicitly, that global warming is happening and is human-caused. [9] [10] It is "extremely likely" [11] that this warming arises from "human activities, especially emissions of greenhouse gases" [11] in the atmosphere. [12] Natural change alone would have had a slight cooling effect rather than a warming effect. [13] [14] [15] [16]

This scientific opinion is expressed in synthesis reports, by scientific bodies of national or international standing, and by surveys of opinion among climate scientists. Individual scientists, universities, and laboratories contribute to the overall scientific opinion via their peer-reviewed publications, and the areas of collective agreement and relative certainty are summarised in these respected reports and surveys. [17] The IPCC's Fifth Assessment Report (AR5) was completed in 2014. [18] Its conclusions are summarized below:

  • "Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia." [19]
  • "Atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years." [20]
  • Human influence on the climate system is clear. [21] It is extremely likely (95–100% probability) [22] that human influence was the dominant cause of global warming between 1951 and 2010. [21]
  • "Increasing magnitudes of [global] warming increase the likelihood of severe, pervasive, and irreversible impacts." [23]
  • "A first step towards adaptation to future climate change is reducing vulnerability and exposure to present climate variability." [24]
  • "The overall risks of climate change impacts can be reduced by limiting the rate and magnitude of climate change" [23]
  • Without new policies to mitigate climate change, projections suggest an increase in global mean temperature in 2100 of 3.7 to 4.8 °C, relative to pre-industrial levels (median values the range is 2.5 to 7.8 °C including climate uncertainty). [25]
  • The current trajectory of global greenhouse gas emissions is not consistent with limiting global warming to below 1.5 or 2 °C, relative to pre-industrial levels. [26] Pledges made as part of the Cancún Agreements are broadly consistent with cost-effective scenarios that give a "likely" chance (66–100% probability) of limiting global warming (in 2100) to below 3 °C, relative to pre-industrial levels. [27]

National and international science academies and scientific societies have assessed current scientific opinion on global warming. These assessments are generally consistent with the conclusions of the Intergovernmental Panel on Climate Change.

Some scientific bodies have recommended specific policies to governments, and science can play a role in informing an effective response to climate change. Policy decisions, however, may require value judgements and so are not included in the scientific opinion. [29] [30]

No scientific body of national or international standing maintains a formal opinion dissenting from any of these main points. The last national or international scientific body to drop dissent was the American Association of Petroleum Geologists, [31] which in 2007 [32] updated its statement to its current non-committal position. [33] Some other organizations, primarily those focusing on geology, also hold non-committal positions.

Synthesis reports are assessments of scientific literature that compile the results of a range of stand-alone studies in order to achieve a broad level of understanding, or to describe the state of knowledge of a given subject. [34]

Intergovernmental Panel on Climate Change (IPCC) 2014

The IPCC Fifth Assessment Report followed the same general format as the Fourth Assessment Report, with three Working Group reports and a Synthesis report. [18] The Working Group I report (WG1) was published in September 2013. [18] The report's Summary for Policymakers stated that warming of the climate system is 'unequivocal' with changes unprecedented over decades to millennia, including warming of the atmosphere and oceans, loss of snow and ice, and sea level rise. Greenhouse gas emissions, driven largely by economic and population growth, have led to greenhouse gas concentrations that are unprecedented in at least the last 800,000 years. These, together with other anthropogenic drivers, are "extremely likely" (where that means more than 95% probability) to have been the dominant cause of the observed global warming since the mid-20th century. [35]

Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems. Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks.

Reporting on the publication of the report, The Guardian said that: [36]

In the end it all boils down to risk management. The stronger our efforts to reduce greenhouse gas emissions, the lower the risk of extreme climate impacts. The higher our emissions, the larger climate changes we'll face, which also means more expensive adaptation, more species extinctions, more food and water insecurities, more income losses, more conflicts, and so forth.

In Washington, President Obama's science adviser, John P. Holdren, cited increased scientific confidence "that the kinds of harm already being experienced from climate change will continue to worsen unless and until comprehensive and vigorous action to reduce emissions is undertaken worldwide."

It went on to say that Ban Ki-moon, the United Nations secretary general, had declared his intention to call a meeting of heads of state in 2014 to develop such a treaty. The last such meeting, in Copenhagen in 2009, the NY Times reported, had ended in disarray. [37]

Intergovernmental Panel on Climate Change (IPCC) 2007

In February 2007, the IPCC released a summary of the forthcoming Fourth Assessment Report. According to this summary, the Fourth Assessment Report found that human actions are "very likely" the cause of global warming, meaning a 90% or greater probability. Global warming in this case was indicated by an increase of 0.75 degrees in average global temperatures over the last 100 years. [38]

The IPCC Fourth Assessment Report stated that:

  • Warming of the climate system is unequivocal, as evidenced by increases in global average air and ocean temperatures, the widespread melting of snow and ice, and rising global average sea level. [39]
  • Most of the global warming since the mid-20th century is very likely due to human activities. [40]
  • Benefits and costs of climate change for [human] society will vary widely by location and scale. [41] Some of the effects in temperate and polar regions will be positive, and others elsewhere will be negative. [41] Overall, net effects are more likely to be strongly negative with larger or more rapid warming. [41]
  • The range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time. [42]
  • The resilience of many ecosystems is likely to be exceeded this century by an unprecedented combination of climate change, associated disturbances (e.g. flooding, drought, wildfire, insects, ocean acidification), and other global change drivers (e.g. land-use change, pollution, fragmentation of natural systems, over-exploitation of resources). [43]

The New York Times reported that "the leading international network of climate scientists has concluded for the first time that global warming is 'unequivocal' and that human activity is the main driver, 'very likely' causing most of the rise in temperatures since 1950". [44]

A retired journalist for The New York Times, William K. Stevens wrote: "The Intergovernmental Panel on Climate Change said the likelihood was 90 percent to 99 percent that emissions of heat-trapping greenhouse gases like carbon dioxide, spewed from tailpipes and smokestacks, were the dominant cause of the observed warming of the last 50 years. In the panel's parlance, this level of certainty is labeled 'very likely'. Only rarely does scientific odds-making provide a more definite answer than that, at least in this branch of science, and it describes the endpoint, so far, of a progression." [45]

The Associated Press summarized the position on sea level rise: [46]

On sea levels, the report projects rises of 7 to 23 inches by the end of the century. An additional 3.9 to 7.8 inches are possible if recent, surprising melting of polar ice sheets continues.

U.S. Global Change Research Program

Thirteen federal agencies, led by the National Oceanic and Atmospheric Administration (NOAA), worked together under the auspices of the United States Global Change Research Program (USGCRP) to prepare the country's Fourth National Climate Assessment, published in two volumes as described below.

The Climate Science Special Report: Fourth National Climate Assessment, Volume I (October 2017) provided the following summary:

This assessment concludes, based on extensive evidence, that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.

Background

Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases. These emissions come mainly from the burning of fossil fuels (coal, oil, and gas), with important contributions from the clearing of forests, agricultural practices, and other activities.

The 2009 report, which is about the effects that climate change is having in the United States, also said:

Climate-related changes have already been observed globally and in the United States. These include increases in air and water temperatures, reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, permafrost, and sea ice. A longer ice-free period on lakes and rivers, lengthening of the growing season, and increased water vapor in the atmosphere have also been observed. Over the past 30 years, temperatures have risen faster in winter than in any other season, with average winter temperatures in the Midwest and northern Great Plains increasing more than 7 °F (3.9 °C). Some of the changes have been faster than previous assessments had suggested.

Arctic Climate Impact Assessment

In 2004, the intergovernmental Arctic Council and the non-governmental International Arctic Science Committee released the synthesis report of the Arctic Climate Impact Assessment: [49]

Climate conditions in the past provide evidence that rising atmospheric carbon dioxide levels are associated with rising global temperatures. Human activities, primarily the burning of fossil fuels (coal, oil, and natural gas), and secondarily the clearing of land, have increased the concentration of carbon dioxide, methane, and other heat-trapping ("greenhouse") gases in the atmosphere. . There is international scientific consensus that most of the warming observed over the last 50 years is attributable to human activities. [50]

There is an extensive discussion in the scientific literature on what policies might be effective in responding to climate change. [51] Some scientific bodies have recommended specific policies to governments (refer to the later sections of the article). [52] The natural and social sciences can play a role in informing an effective response to climate change. [29] However, policy decisions may require value judgements. [29] For example, the US National Research Council has commented: [30]

The question of whether there exists a "safe" level of concentration of greenhouse gases cannot be answered directly because it would require a value judgment of what constitutes an acceptable risk to human welfare and ecosystems in various parts of the world, as well as a more quantitative assessment of the risks and costs associated with the various impacts of global warming. In general, however, risk increases with increases in both the rate and the magnitude of climate change.

This article mostly focuses on the views of natural scientists. However, social scientists, [51] medical experts, [53] engineers [51] and philosophers [54] have also commented on climate change science and policies. Climate change policy is discussed in several articles: climate change mitigation, climate change adaptation, climate engineering, politics of global warming, climate ethics, and economics of global warming.

This is a list of scientific bodies of national or international standing, that have issued formal statements of opinion, classifies those organizations according to whether they concur with the IPCC view, are non-committal, or dissent from it. The California Governor's Office website lists nearly 200 worldwide scientific organizations hold the position that climate change has been caused by human action. [55]

Concurring

Academies of science (general science)

Since 2001, 34 national science academies, three regional academies, and both the international InterAcademy Council and International Council of Academies of Engineering and Technological Sciences have made formal declarations confirming human induced global warming and urging nations to reduce emissions of greenhouse gases. The 34 national science academy statements include 33 who have signed joint science academy statements and one individual declaration by the Polish Academy of Sciences in 2007.

Joint national science academy statements
  • 2001 Following the publication of the IPCC Third Assessment Report, seventeen national science academies issued a joint statement, entitled "The Science of Climate Change", explicitly acknowledging the IPCC position as representing the scientific consensus on climate change science. The statement, printed in an editorial in the journal Science on 18 May 2001, [56] was signed by the science academies of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, Turkey, and the United Kingdom. [57]
  • 2005 The national science academies of the G8 nations, plus Brazil, China and India, three of the largest emitters of greenhouse gases in the developing world, signed a statement on the global response to climate change. The statement stresses that the scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action, and explicitly endorsed the IPCC consensus. The eleven signatories were the science academies of Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, the United Kingdom, and the United States. [58]
  • 2007 In preparation for the 33rd G8 summit, the national science academies of the G8+5 nations issued a declaration referencing the position of the 2005 joint science academies' statement, and acknowledging the confirmation of their previous conclusion by recent research. Following the IPCC Fourth Assessment Report, the declaration states, "It is unequivocal that the climate is changing, and it is very likely that this is predominantly caused by the increasing human interference with the atmosphere. These changes will transform the environmental conditions on Earth unless counter-measures are taken." The thirteen signatories were the national science academies of Brazil, Canada, China, France, Germany, Italy, India, Japan, Mexico, Russia, South Africa, the United Kingdom, and the United States. [59]
  • 2007 In preparation for the 33rd G8 summit, the Network of African Science Academies submitted a joint "statement on sustainability, energy efficiency, and climate change":

A consensus, based on current evidence, now exists within the global scientific community that human activities are the main source of climate change and that the burning of fossil fuels is largely responsible for driving this change. The IPCC should be congratulated for the contribution it has made to public understanding of the nexus that exists between energy, climate and sustainability.

Polish Academy of Sciences

In December 2007, the General Assembly of the Polish Academy of Sciences (Polska Akademia Nauk), which has not been a signatory to joint national science academy statements issued a declaration endorsing the IPCC conclusions, and stating: [62]

it is the duty of Polish science and the national government to, in a thoughtful, organized and active manner, become involved in realisation of these ideas.

Problems of global warming, climate change, and their various negative impacts on human life and on the functioning of entire societies are one of the most dramatic challenges of modern times.

PAS General Assembly calls on the national scientific communities and the national government to actively support Polish participation in this important endeavor.

Additional national science academy and society statements
    as the world's largest general scientific society, adopted an official statement on climate change in 2006: [63]

The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society. . The pace of change and the evidence of harm have increased markedly over the last five years. The time to control greenhouse gas emissions is now.

Global climate change is real and measurable. . To reduce the global net economic, environmental and social losses in the face of these impacts, the policy objective must remain squarely focused on returning greenhouse gas concentrations to near pre-industrial levels through the reduction of emissions. The spatial and temporal fingerprint of warming can be traced to increasing greenhouse gas concentrations in the atmosphere, which are a direct result of burning fossil fuels, broad-scale deforestation and other human activity.

The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability. Human-induced warming and associated sea level rises are expected to continue through the 21st century. . The IPCC's conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue.

The globe is warming because of increasing greenhouse gas emissions. Measurements show that greenhouse gas concentrations in the atmosphere are well above levels seen for many thousands of years. Further global climate changes are predicted, with impacts expected to become more costly as time progresses. Reducing future impacts of climate change will require substantial reductions of greenhouse gas emissions.

There is strong evidence that the warming of the Earth over the last half-century has been caused largely by human activity, such as the burning of fossil fuels and changes in land use, including agriculture and deforestation.

International science academies
    in 2007 was a signatory to the "statement on sustainability, energy efficiency, and climate change". This joint statement of African science academies, was organized through the Network of African Science Academies. Its stated goal was "to convey information and spur action on the occasion of the G8 Summit in Heiligendamm, Germany, in June 2007": [71]

A consensus, based on current evidence, now exists within the global scientific community that human activities are the main source of climate change and that the burning of fossil fuels is largely responsible for driving this change.

Human activity is most likely responsible for climate warming. Most of the climatic warming over the last 50 years is likely to have been caused by increased concentrations of greenhouse gases in the atmosphere. Documented long-term climate changes include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones. The above development potentially has dramatic consequences for mankind's future.

There is now convincing evidence that since the industrial revolution, human activities, resulting in increasing concentrations of greenhouse gases have become a major agent of climate change . On-going and increased efforts to mitigate climate change through reduction in greenhouse gases are therefore crucial.

Current patterns of energy resources and energy usage are proving detrimental to the long-term welfare of humanity. The integrity of essential natural systems is already at risk from climate change caused by the atmospheric emissions of greenhouse gases. [76] Concerted efforts should be mounted for improving energy efficiency and reducing the carbon intensity of the world economy. [77]

As reported by the Intergovernmental Panel on Climate Change (IPCC), most of the observed global warming since the mid-20th century is very likely due to human-produced emission of greenhouse gases and this warming will continue unabated if present anthropogenic emissions continue or, worse, expand without control. CAETS, therefore, endorses the many recent calls to decrease and control greenhouse gas emissions to an acceptable level as quickly as possible.

Physical and chemical sciences

Earth sciences

American Geophysical Union

The American Geophysical Union (AGU) adopted a statement on Climate Change and Greenhouse Gases in 1998. [84] A new statement, adopted by the society in 2003, revised in 2007, [85] and revised and expanded in 2013, [86] affirms that rising levels of greenhouse gases have caused and will continue to cause the global surface temperature to be warmer:

Human activities are changing Earth's climate. At the global level, atmospheric concentrations of carbon dioxide and other heat-trapping greenhouse gases have increased sharply since the Industrial Revolution. Fossil fuel burning dominates this increase. Human-caused increases in greenhouse gases are responsible for most of the observed global average surface warming of roughly 0.8 °C (1.5 °F) over the past 140 years. Because natural processes cannot quickly remove some of these gases (notably carbon dioxide) from the atmosphere, our past, present, and future emissions will influence the climate system for millennia. While important scientific uncertainties remain as to which particular impacts will be experienced where, no uncertainties are known that could make the impacts of climate change inconsequential. Furthermore, surprise outcomes, such as the unexpectedly rapid loss of Arctic summer sea ice, may entail even more dramatic changes than anticipated.

American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

In May 2011, the American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Soil Science Society of America (SSSA) issued a joint position statement on climate change as it relates to agriculture: [87]

A comprehensive body of scientific evidence indicates beyond reasonable doubt that global climate change is now occurring and that its manifestations threaten the stability of societies as well as natural and managed ecosystems. Increases in ambient temperatures and changes in related processes are directly linked to rising anthropogenic greenhouse gas (GHG) concentrations in the atmosphere.

Unless the emissions of GHGs are curbed significantly, their concentrations will continue to rise, leading to changes in temperature, precipitation, and other climate variables that will undoubtedly affect agriculture around the world.

Climate change has the potential to increase weather variability as well as gradually increase global temperatures. Both of these impacts have the potential to negatively impact the adaptability and resilience of the world's food production capacity current research indicates climate change is already reducing the productivity of vulnerable cropping systems.

European Federation of Geologists

In 2008, the European Federation of Geologists [88] (EFG) issued the position paper Carbon Capture and geological Storage: [89]

The EFG recognizes the work of the IPCC and other organizations, and subscribes to the major findings that climate change is happening, is predominantly caused by anthropogenic emissions of CO
2 , and poses a significant threat to human civilization.

It is clear that major efforts are necessary to quickly and strongly reduce CO
2 emissions. The EFG strongly advocates renewable and sustainable energy production, including geothermal energy, as well as the need for increasing energy efficiency.

CCS [Carbon Capture and geological Storage] should also be regarded as a bridging technology, facilitating the move towards a carbon free economy.

European Geosciences Union

In 2005, the Divisions of Atmospheric and Climate Sciences of the European Geosciences Union (EGU) issued a position statement in support of the Joint national science academy statements on global response to climate change. The statement refers to the Intergovernmental Panel on Climate Change (IPCC), as "the main representative of the global scientific community", and asserts that the IPCC: [90]

represents the state-of-the-art of climate science supported by the major science academies around the world and by the vast majority of science researchers and investigators as documented by the peer-reviewed scientific literature.

Additionally, in 2008, the EGU issued a position statement on ocean acidification which states, "Ocean acidification is already occurring today and will continue to intensify, closely tracking atmospheric CO
2 increase. Given the potential threat to marine ecosystems and its ensuing impact on human society and economy, especially as it acts in conjunction with anthropogenic global warming, there is an urgent need for immediate action." The statement then advocates for strategies "to limit future release of CO
2 to the atmosphere and/or enhance removal of excess CO
2 from the atmosphere". [91] And, in 2018 the EGU issued a statement concurring with the findings of the Special Report on Global Warming of 1.5 °C, with Jonathan Bamber, president of the organisation, noting: "EGU concurs with, and supports, the findings of the SR15 that action to curb the most dangerous consequences of human-induced climate change is urgent, of the utmost importance and the window of opportunity extremely limited." [92]

Geological Society of America

In 2006, the Geological Society of America adopted a position statement on global climate change. It amended this position on 20 April 2010, with more explicit comments on need for CO
2 reduction: [93]

Decades of scientific research have shown that climate can change from both natural and anthropogenic causes. The Geological Society of America (GSA) concurs with assessments by the National Academies of Science (2005), the National Research Council (2006), and the Intergovernmental Panel on Climate Change (IPCC, 2007) that global climate has warmed and that human activities (mainly greenhouse‐gas emissions) account for most of the warming since the middle 1900s. If current trends continue, the projected increase in global temperature by the end of the twenty first century will result in large impacts on humans and other species. Addressing the challenges posed by climate change will require a combination of adaptation to the changes that are likely to occur and global reductions of CO
2 emissions from anthropogenic sources.

Geological Society of London

In November 2010, the Geological Society of London issued the position statement Climate change: evidence from the geological record: [94]

The last century has seen a rapidly growing global population and much more intensive use of resources, leading to greatly increased emissions of gases, such as carbon dioxide and methane, from the burning of fossil fuels (oil, gas and coal), and from agriculture, cement production and deforestation. Evidence from the geological record is consistent with the physics that shows that adding large amounts of carbon dioxide to the atmosphere warms the world and may lead to: higher sea levels and flooding of low-lying coasts greatly changed patterns of rainfall increased acidity of the oceans and decreased oxygen levels in seawater. There is now widespread concern that the Earth's climate will warm further, not only because of the lingering effects of the added carbon already in the system, but also because of further additions as human population continues to grow. Life on Earth has survived large climate changes in the past, but extinctions and major redistribution of species have been associated with many of them. When the human population was small and nomadic, a rise in sea level of a few metres would have had very little effect on Homo sapiens. With the current and growing global population, much of which is concentrated in coastal cities, such a rise in sea level would have a drastic effect on our complex society, especially if the climate were to change as suddenly as it has at times in the past. Equally, it seems likely that as warming continues some areas may experience less precipitation leading to drought. With both rising seas and increasing drought, pressure for human migration could result on a large scale.

International Union of Geodesy and Geophysics

In July 2007, the International Union of Geodesy and Geophysics (IUGG) adopted a resolution titled "The Urgency of Addressing Climate Change". In it, the IUGG concurs with the "comprehensive and widely accepted and endorsed scientific assessments carried out by the Intergovernmental Panel on Climate Change and regional and national bodies, which have firmly established, on the basis of scientific evidence, that human activities are the primary cause of recent climate change". They state further that the "continuing reliance on combustion of fossil fuels as the world's primary source of energy will lead to much higher atmospheric concentrations of greenhouse gases, which will, in turn, cause significant increases in surface temperature, sea level, ocean acidification, and their related consequences to the environment and society". [95]

National Association of Geoscience Teachers

In July 2009, the National Association of Geoscience Teachers [96] (NAGT) adopted a position statement on climate change in which they assert that "Earth's climate is changing [and] "that present warming trends are largely the result of human activities": [97]

NAGT strongly supports and will work to promote education in the science of climate change, the causes and effects of current global warming, and the immediate need for policies and actions that reduce the emission of greenhouse gases.

Meteorology and oceanography

American Meteorological Society

The American Meteorological Society (AMS) statement adopted by their council in 2012 concluded: [98]

There is unequivocal evidence that Earth's lower atmosphere, ocean, and land surface are warming sea level is rising and snow cover, mountain glaciers, and Arctic sea ice are shrinking. The dominant cause of the warming since the 1950s is human activities. This scientific finding is based on a large and persuasive body of research. The observed warming will be irreversible for many years into the future, and even larger temperature increases will occur as greenhouse gases continue to accumulate in the atmosphere. Avoiding this future warming will require a large and rapid reduction in global greenhouse gas emissions. The ongoing warming will increase risks and stresses to human societies, economies, ecosystems, and wildlife through the 21st century and beyond, making it imperative that society respond to a changing climate. To inform decisions on adaptation and mitigation, it is critical that we improve our understanding of the global climate system and our ability to project future climate through continued and improved monitoring and research. This is especially true for smaller (seasonal and regional) scales and weather and climate extremes, and for important hydroclimatic variables such as precipitation and water availability. Technological, economic, and policy choices in the near future will determine the extent of future impacts of climate change. Science-based decisions are seldom made in a context of absolute certainty. National and international policy discussions should include consideration of the best ways to both adapt to and mitigate climate change. Mitigation will reduce the amount of future climate change and the risk of impacts that are potentially large and dangerous. At the same time, some continued climate change is inevitable, and policy responses should include adaptation to climate change. Prudence dictates extreme care in accounting for our relationship with the only planet known to be capable of sustaining human life.

A 2016 survey found that two-thirds of AMS members think that all or most of climate change is caused by human activity. [99]

Australian Meteorological and Oceanographic Society

The Australian Meteorological and Oceanographic Society has issued a Statement on Climate Change, wherein they conclude: [100]

Global climate change and global warming are real and observable . It is highly likely that those human activities that have increased the concentration of greenhouse gases in the atmosphere have been largely responsible for the observed warming since 1950. The warming associated with increases in greenhouse gases originating from human activity is called the enhanced greenhouse effect. The atmospheric concentration of carbon dioxide has increased by more than 30% since the start of the industrial age and is higher now than at any time in at least the past 650,000 years. This increase is a direct result of burning fossil fuels, broad-scale deforestation and other human activity.

Canadian Foundation for Climate and Atmospheric Sciences

We concur with the climate science assessment of the Intergovernmental Panel on Climate Change (IPCC) in 2001 . We endorse the conclusions of the IPCC assessment that 'There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities'. . There is increasingly unambiguous evidence of changing climate in Canada and around the world. There will be increasing impacts of climate change on Canada's natural ecosystems and on our socio-economic activities. Advances in climate science since the 2001 IPCC Assessment have provided more evidence supporting the need for action and development of a strategy for adaptation to projected changes.

Canadian Meteorological and Oceanographic Society

In November 2009, a letter to the Canadian Parliament by The Canadian Meteorological and Oceanographic Society states: [102]

Rigorous international research, including work carried out and supported by the Government of Canada, reveals that greenhouse gases resulting from human activities contribute to the warming of the atmosphere and the oceans and constitute a serious risk to the health and safety of our society, as well as having an impact on all life.

Royal Meteorological Society (UK)

In February 2007, after the release of the IPCC's Fourth Assessment Report, the Royal Meteorological Society issued an endorsement of the report. In addition to referring to the IPCC as "[the] world's best climate scientists", they stated that climate change is happening as "the result of emissions since industrialization and we have already set in motion the next 50 years of global warming – what we do from now on will determine how worse it will get." [103]

World Meteorological Organization

In its Statement at the Twelfth Session of the Conference of the Parties to the U.N. Framework Convention on Climate Change presented on 15 November 2006, the World Meteorological Organization (WMO) confirms the need to "prevent dangerous anthropogenic interference with the climate system". The WMO concurs that "scientific assessments have increasingly reaffirmed that human activities are indeed changing the composition of the atmosphere, in particular through the burning of fossil fuels for energy production and transportation". The WMO concurs that "the present atmospheric concentration of CO
2 was never exceeded over the past 420,000 years" and that the IPCC "assessments provide the most authoritative, up-to-date scientific advice". [104]

American Quaternary Association

Few credible scientists now doubt that humans have influenced the documented rise in global temperatures since the Industrial Revolution. The first government-led U.S. Climate Change Science Program synthesis and assessment report supports the growing body of evidence that warming of the atmosphere, especially over the past 50 years, is directly impacted by human activity.

International Union for Quaternary Research

The statement on climate change issued by the International Union for Quaternary Research (INQUA) reiterates the conclusions of the IPCC, and urges all nations to take prompt action in line with the UNFCCC principles: [106]

Human activities are now causing atmospheric concentrations of greenhouse gases—including carbon dioxide, methane, tropospheric ozone, and nitrous oxide—to rise well above pre-industrial levels . Increases in greenhouse gases are causing temperatures to rise . The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action . Minimizing the amount of this carbon dioxide reaching the atmosphere presents a huge challenge but must be a global priority.

Biology and life sciences

Life science organizations have outlined the dangers climate change pose to wildlife.

  • American Association of Wildlife Veterinarians [107] . In October 2009, the leaders of 18 US scientific societies and organizations sent an open letter to the United States Senate reaffirming the scientific consensus that climate change is occurring and is primarily caused by human activities. The American Institute of Biological Sciences (AIBS) adopted this letter as their official position statement. [108][109] The letter goes on to warn of predicted impacts on the United States such as sea level rise and increases in extreme weather events, water scarcity, heat waves, wildfires, and the disturbance of biological systems. It then advocates for a dramatic reduction in emissions of greenhouse gases. [110][111]
  • Australian Coral Reef Society [112] (UK) [113] issued two position statements pertaining to climate change in which they cite the IPCC [114] and the UNFCCC. [115] (international) [116]

Human health

A number of health organizations have warned about the numerous negative health effects of global warming:

There is now widespread agreement that the Earth is warming, due to emissions of greenhouse gases caused by human activity. It is also clear that current trends in energy use, development, and population growth will lead to continuing – and more severe – climate change.

The changing climate will inevitably affect the basic requirements for maintaining health: clean air and water, sufficient food and adequate shelter. Each year, about 800,000 people die from causes attributable to urban air pollution, 1.8 million from diarrhoea resulting from lack of access to clean water supply, sanitation, and poor hygiene, 3.5 million from malnutrition and approximately 60,000 in natural disasters. A warmer and more variable climate threatens to lead to higher levels of some air pollutants, increase transmission of diseases through unclean water and through contaminated food, to compromise agricultural production in some of the least developed countries, and increase the hazards of extreme weather.

The Bulletin of the Atomic Scientists and "Doomsday clock"

In 1945, Albert Einstein and other scientists who created atomic weapons used in the atomic bombings of Hiroshima and Nagasaki founded the "Bulletin of the Atomic Scientists" and created the "Doomsday Clock". The goal of the clock is to convey threats to humanity and the planet, and to create public awareness that will lead to solutions. In the beginning, the Doomsday Clock focused on the dangers of nuclear war, but in the 21th century, it has begun to deal with other issues like climate change and disinformation on the internet.

On 23 January 2020 the organization moved the doomsday clock to 100 seconds before midnight, closer than ever. It explained that it did it because of three factors:

  • Increasing danger of nuclear war,
  • Increasing danger from climate change, and
  • Increasing danger from disinformation in the internet regarding the issues in points 1 and 2 and other "disruptive technologies".

The organization praised the climate movement of young people and called to citizens and governments to act to take greater action on climate change. [125]

Miscellaneous

A number of other national scientific societies have also endorsed the opinion of the IPCC:

    [126][127][128]
  • The Institution of Engineers Australia[129]
  • International Association for Great Lakes Research [130]
  • Institute of Professional Engineers New Zealand [131] (WFEO)

Non-committal

American Association of Petroleum Geologists

As of June 2007, the American Association of Petroleum Geologists (AAPG) Position Statement on climate change stated: [132]

the AAPG membership is divided on the degree of influence that anthropogenic CO
2 has on recent and potential global temperature increases . Certain climate simulation models predict that the warming trend will continue, as reported through NAS, AGU, AAAS and AMS. AAPG respects these scientific opinions but wants to add that the current climate warming projections could fall within well-documented natural variations in past climate and observed temperature data. These data do not necessarily support the maximum case scenarios forecast in some models.

Prior to the adoption of this statement, the AAPG was the only major scientific organization that rejected the finding of significant human influence on recent climate, according to a statement by the Council of the American Quaternary Association. [31] Explaining the plan for a revision, AAPG president Lee Billingsly wrote in March 2007: [133]

Members have threatened to not renew their memberships . if AAPG does not alter its position on global climate change . And I have been told of members who already have resigned in previous years because of our current global climate change position . The current policy statement is not supported by a significant number of our members and prospective members.

AAPG President John Lorenz announced the "sunsetting" of AAPG's Global Climate Change Committee in January 2010. The AAPG Executive Committee determined: [134]

Climate change is peripheral at best to our science . AAPG does not have credibility in that field . and as a group we have no particular knowledge of global atmospheric geophysics.

American Institute of Professional Geologists (AIPG)

The official position statement from AIPG on the Environment states that "combustion of fossil fuel include and the generation of GHGs [greenhouse gases] including carbon dioxide (CO2) and methane (CH4). Emissions of GHGs are perceived by some to be one of the largest, global environmental concerns related to energy production due to potential effects on the global energy system and possibly global climate. Fossil fuel use is the primary source of the increased atmospheric concentration of GHGs since industrialization". [135]

In March 2010, AIPG's Executive Director issued a statement regarding polarization of opinions on climate change within the membership and announced that the AIPG Executive had made a decision to cease publication of articles and opinion pieces concerning climate change in AIPG's news journal, The Professional Geologist. [136]

Opposing

Since 2007, when the American Association of Petroleum Geologists released a revised statement, [32] no longer does any national or international scientific body reject the findings of human-induced effects on climate change. [31] [33]

Various surveys have been conducted to evaluate scientific opinion on global warming. They have concluded that almost all climate scientists support the idea of anthropogenic climate change. [1]

In 2004, the geologist and historian of science Naomi Oreskes summarized a study of the scientific literature on climate change. [137] She analyzed 928 abstracts of papers from refereed scientific journals between 1993 and 2003 and concluded that there is a scientific consensus on the reality of anthropogenic climate change.

Oreskes divided the abstracts into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position. Seventy-five per cent of the abstracts were placed in the first three categories (either explicitly or implicitly accepting the consensus view) 25% dealt with methods or paleoclimate, thus taking no position on current anthropogenic climate change. None of the abstracts disagreed with the consensus position, which the author found to be "remarkable". According to the report, "authors evaluating impacts, developing methods, or studying paleoclimatic change might believe that current climate change is natural. However, none of these papers argued that point."

In 2007, Harris Interactive surveyed 489 randomly selected members of either the American Meteorological Society or the American Geophysical Union for the Statistical Assessment Service (STATS) at George Mason University. 97% of the scientists surveyed agreed that global temperatures had increased during the past 100 years 84% said they personally believed human-induced warming was occurring, and 74% agreed that "currently available scientific evidence" substantiated its occurrence. Catastrophic effects in 50–100 years would likely be observed according to 41%, while 44% thought the effects would be moderate and about 13 percent saw relatively little danger. 5% said they thought human activity did not contribute to greenhouse warming. [138] [139] [140] [141]

Dennis Bray and Hans von Storch conducted a survey in August 2008 of 2058 climate scientists from 34 different countries. [142] A web link with a unique identifier was given to each respondent to eliminate multiple responses. A total of 373 responses were received giving an overall response rate of 18.2%. No paper on climate change consensus based on this survey has been published yet (February 2010), but one on another subject has been published based on the survey. [143]

The survey was made up of 76 questions split into a number of sections. There were sections on the demographics of the respondents, their assessment of the state of climate science, how good the science is, climate change impacts, adaptation and mitigation, their opinion of the IPCC, and how well climate science was being communicated to the public. Most of the answers were on a scale from 1 to 7 from "not at all" to "very much".

To the question "How convinced are you that climate change, whether natural or anthropogenic, is occurring now?", 67.1% said they very much agreed, 26.7% agreed to some large extent, 6.2% said to they agreed to some small extent (2–4), none said they did not agree at all. To the question "How convinced are you that most of recent or near future climate change is, or will be, a result of anthropogenic causes?" the responses were 34.6% very much agree, 48.9% agreeing to a large extent, 15.1% to a small extent, and 1.35% not agreeing at all.

A poll performed by Peter Doran and Maggie Kendall Zimmerman at University of Illinois at Chicago received replies from 3,146 of the 10,257 polled Earth scientists. Results were analyzed globally and by specialization. 76 out of 79 climatologists who "listed climate science as their area of expertise and who also have published more than 50% of their recent peer-reviewed papers on the subject of climate change" believed that mean global temperatures had risen compared to pre-1800s levels. Seventy-five of 77 believed that human activity is a significant factor in changing mean global temperatures. Among all respondents, 90% agreed that temperatures have risen compared to pre-1800 levels, and 82% agreed that humans significantly influence the global temperature. Economic geologists and meteorologists were among the biggest doubters, with only 47 percent and 64 percent, respectively, believing in significant human involvement. The authors summarised the findings: [144]

It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes.

A 2010 paper in the Proceedings of the National Academy of Sciences of the United States (PNAS) reviewed publication and citation data for 1,372 climate researchers and drew the following two conclusions: [145]

(i) 97–98% of the climate researchers most actively publishing in the field support the tenets of ACC (Anthropogenic Climate Change) outlined by the Intergovernmental Panel on Climate Change, and (ii) the relative climate expertise and scientific prominence of the researchers unconvinced of ACC are substantially below that of the convinced researchers.

A 2013 paper in Environmental Research Letters reviewed 11,944 abstracts of scientific papers matching "global warming" or "global climate change". They found 4,014 which discussed the cause of recent global warming, and of these "97.1% endorsed the consensus position that humans are causing global warming". [146] This study was criticised in 2016 by Richard Tol, [147] but strongly defended by a companion paper in the same volume. [148]

A 2012 analysis of published research on global warming and climate change between 1991 and 2012 found that of the 13,950 articles in peer-reviewed journals, only 24 rejected anthropogenic global warming. [149] A follow-up analysis looking at 2,258 peer-reviewed climate articles with 9,136 authors published between November 2012 and December 2013 revealed that only one of the 9,136 authors rejected anthropogenic global warming. [150] His 2015 paper on the topic, covering 24,210 articles published by 69,406 authors during 2013 and 2014 found only five articles by four authors rejecting anthropogenic global warming. Over 99.99% of climate scientists did not reject AGW in their peer-reviewed research. [151]

James Lawrence Powell reported in 2017 that using rejection as the criterion of consensus, five surveys of the peer-reviewed literature from 1991 to 2015, including several of those above, combine to 54,195 articles with an average consensus of 99.94%. [152] In November 2019, his survey of over 11,600 peer-reviewed articles published in the first seven months of 2019 showed that the consensus had reached 100%. [153]

A question that frequently arises in popular discussion is whether there is a scientific consensus on climate change. [17] Several scientific organizations have explicitly used the term "consensus" in their statements:


Impact on animals

Several studies this year focused on the effects of climate change on plants and animals, including this one about the dwindling supply of a fungus that serves as a major source of income in parts of the Himalayas.

Stanford researchers tracked pikas in the Indian Himalayas and took small samples of their blood in order to analyze how their genes were helping them adapt to different oxygen levels. (Image credit: Katie Solari)

Elsewhere in the Himalayas, mammals known as pikas are being driven to higher elevations as they flee the warming weather. A new study found reassuring news in the pikas’ genes – the animals are able to activate genes that allow them to use oxygen more efficiently as they move higher.

A story about the work describes the researchers’ pika-sized test equipment and modified high-altitude training chambers used to assess the animals’ adaptability. “We’re used to thinking about genetic adaptation taking thousands of years to occur in a species, but what’s exciting about this work is that this flexibility in gene expression could give at least the lower-elevation pika populations a better chance than we thought of being able to adapt to climate change on these short timescales,” said Elizabeth Hadly, the Paul S. and Billie Achilles Professor in Environmental Biology and senior author of the study.

In Canada, where the Peace-Athabasca Delta is slowly drying, another team of researchers studied a different mammal – the muskrat. With easy to find homes, muskrats are easy to count and serve as an indicator for species in the area. The team found that as freshwater areas dwindled, so too did muskrat homes.

“The ecological impacts are not limited to muskrat – they extend far beyond that,” doctoral student Ellen Ward said in a story about the work. “These results suggest that maybe the widespread continental-scale decline in this animal is actually being driven by a large-scale loss in wetland and aquatic habitat.”

But finally, it wasn’t all bad. As a doctoral student studying the fate of the yellow cedar tree in Southeast Alaska, Lauren Oakes, now a lecturer in the Emmett Interdisciplinary Program in Environment and Resources, found inspiration in how communities came together. In a story about her new book, Oakes said, “I feel that hope is this idea that somebody else might fix it. We’re looking for policy, or looking for everyone to get onboard with the Paris Agreement, or looking for President Trump to turn around, but I think more can come from individual action.”


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