Global warming controversy

The global warming controversy is a decades-old dispute about the effects of humans on the global climate.

This article is about that controversy. The description and scientific explanation of global warming is spread over several articles:


Controversial issues

The controversy is made up of separate issues relating to global warming which are sometimes mixed together by proponents of one view or another.

  1. Whether or not the climate is changing beyond natural variations (historical temperature record).
  2. Whether or not human/industrial activity is responsible for the change (attribution of recent climate change).
  3. How large future changes will be.
  4. What will be the consequences of climate change.
  5. What are the best responses to climate change.
  6. Whether decisions require less uncertainty.

Much of the discussion centers on the effect of emissions of carbon dioxide related to human activity ranging from burning fossil-fuels to industrial activity. But this alone would be a scientific argument confined to the scientific press. The point that leads to major controversy—because it could have significant economic impacts—is whether action (usually, restrictions on the use of fossil fuels to reduce carbon dioxide emissions) should be taken now or in the near future and whether those restrictions would have any meaningful effect on global temperature.

Because of the economic ramifications of such restrictions, there are those who feel strongly that, even if global warming is caused solely by the burning of fossil fuels, restricting their use would have more damaging effects on the world economy than the increases in global temperature. In contrast, others feel strongly that early action to reduce emissions would help avoid much greater economic costs later and would reduce the risk of catastrophic, irreversible change.

Scope of the controversy

The controversy occurs almost entirely within the press and political arenas. In the scientific press and among climate researchers, there is little controversy about global warming, only a desire to investigate a scientific problem and possible consequences. As Kevin E. Trenberth writes:

In 1995 the IPCC assessment concluded that "the balance of evidence suggests that there is a discernible human influence on global climate". Since then the evidence has become much stronger ... Thus the headline in IPCC (2001) is "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities"... While some changes arising from global warming are benign or even beneficial, the economic effects of the weather extremes are substantial and clearly warrant attention in policy debates... Consequently, there is a strong case for slowing down the projected rates of climate change from human influences. [1] (

Trenberth also provides evidence for the controversy that occurs when science meets the political arena:

The SPM was approved line by line by governments... The argument here is that the scientists determine what can said, but the governments determine how it can best be said. Negotiations occur over wording to ensure accuracy, balance, clarity of message, and relevance to understanding and policy. The IPCC process is dependent on the good will of the participants in producing a balanced assessment. However, in Shanghai, it appeared that there were attempts to blunt, and perhaps obfuscate, the messages in the report, most notably by Saudi Arabia. This led to very protracted debates over wording on even bland and what should be uncontroversial text... The most contentious paragraph in the IPCC (2001) SPM was the concluding one on attribution. After much debate the following was carefully crafted: "In the light of new evidence, and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations." [2] (

Critics of GWT and/or the IPCC point out that the majority of the temperature change has occurred before the majority of the carbon dioxide has been released into the atmosphere.

The arguments over global warming are viewed differently in different parts of the world. In Europe for example global warming has gained wider acceptance than in other parts of the world, most notably the United States.

Points made by supporters of the global warming theory

Supporters of the global warming theory assert that:

Opponents of GWT maintain some or all of these assertions are not proven or not correct.

Proponents of global warming tend to support the IPCC position and thus represent a broadly unified viewpoint, though with considerable differences over what action should be taken. Optionally, supporters may go on to point out that there is a good chance that the future changes may be undesirable, and that planning to avoid or mitigate them would be a good idea.

Participation in the IPCC process does not imply endorsement of it. However, only 2 of the 120 contributing authors to the IPCC TAR are known to have voiced any complaint.

Supporters of the global warming theory

Organisations that support the global warming theory (or at least that have issued supportive declarations) include:

Points made by opponents of the global warming theory

There are many reasons given for opposition to the global warming theory:

  • IPCC draws firm conclusions unjustified by the science, especially given the acknowledged weakness of cloud physics in the climate models. For example, even those who accept that there is a warming trend point out that there is a big difference between correlation and causality. In other words, just because temperatures have generally been rising since the beginning of the Industrial Revolution, that doesn't necessarily mean that the Industrial Revolution has caused the change in temperature (see post hoc, ergo propter hoc argument). On the other hand, the period since the beginning of the Industrial Revolution has indeed produced ever-growing "urban heat islands" (see below) that could be skewing temperature measurements that indicate the recent warming.
  • Using "consensus" as evidence is an appeal to the majority argument rather than scientific discussion (see consensus science). Ergo, because the issue has become so politicized, it is suspected that climatologists who disagree with the consensus as it is may be afraid to speak out for fear of losing their positions or funding.
  • Earth's climate has been both colder and warmer than today, and these changes are adequately explained by mechanisms that do not involve human greenhouse gas emissions.
  • There is no significant global warming relative to the expected natural trends.
  • Climate science can not make definitive predictions yet, since the computer models used to make these predictions are still evolving and do not yet take into account recently discovered feedback mechanisms.
  • Climate models will never be able to predict the future climate, until they can predict solar and volcanic activity.
  • Global warming studies have errors or have not been reproduced.
  • Since carbon dioxide levels have no significant impact on global temperatures, support for the Kyoto Protocol is entirely misguided.
  • Global temperatures are directly related to sunspot activity.

Some opponents of global warming theory give more weight to data such as paleoclimatic studies, temperature measurements made from weather balloons, and satellites which they claim show less warming than surface land and sea records.

Opponents tend to define themselves in terms of opposition to the IPCC position. They generally believe that climate science is not yet able to provide us with solid answers to all the major questions about the global climate.

Opponents frequently characterise supporters arguments as alarmist and premature, so as to emphasise what they perceive as the lack of scientific evidence supporting global warming scenarios.

Opponents also say that if global warning is real and man-made, no action need be taken now because:

  • Future scientific advances or engineering projects will remedy the problem before it becomes serious and for less money.
  • A small amount of global warming would be benign or even beneficial, as increased carbon dioxide would benefit plant life, thus potentially becoming profitable for agriculture world-wide.
  • There is a distinct correlation between GDP growth and greenhouse gas emissions. A cutback in emissions would lead to a decrease in the rate of GDP growth.

Opponents of the global warming theory

Some of the most visible opponents of the global warming theory from within the scientific community have been

Some prominent opponents from outside the science community have been:

Some organisations were formed to further the opponents' views:

Counting experts / Petitions and attacks on them

The proportion of scientists who support or oppose any of the global warming theories is a matter of controversy in its own right. Environmental groups, many governmental reports, and the non-US media often claim virtually unanimous support for the global warming theory from the scientific community. Some opponents maintain that it is the other way around, claiming that the majority of scientists either consider global warming "unproven" or even dismiss it altogether (see global warming skepticism). Other opponents decry the dangers of consensus science, which would imply that they do believe there is a consensus.

A 2004 essay in Science [7] ( surveyed abstracts of peer-reviewed research articles related to climate change. It concluded that a scientific consensus in favor of the global warming theory exists.

Global warming skeptics dispute the claim that (or relevance of) a consensus of scientists supports the view of global warming presented by the IPCC, and say that even the IPCC report authors do not all support the reports. However, of the 120 lead authors of the TAR, only two are known to have complained. In fact, they say, the consensus of those who expend the effort to comment is moving in the opposite direction. Others dispute this. To support this claim, the website of S. Fred Singer's Science and Environmental Policy Project (SEPP) lists four separate petitions:

  • The 1992 "Statement by Atmospheric Scientists on Greenhouse Warming" ("...Such policy initiatives [those concerning the Earth Summit is scheduled to convene in Brazil in June 1992] derive from highly uncertain scientific theories. They are based on the unsupported assumption that catastrophic global warming follows from the burning of fossil fuels and requires immediate action. We do not agree.") [8] (
  • The "Heidelberg Appeal" (also from 1992)
  • Singer's own "Leipzig Declaration on Global Climate Change" (1995 and 1997)
  • The "Oregon Petition," which was circulated in 1998 by physicist Frederick Seitz.

According to SEPP associate Candace Crandall, these petitions show that "the number of scientists refuting global warming is growing." [9] ( However, people who have examinated the petitions challenge that conclusion, pointing out that:

  1. The 1992 "Statement by Atmospheric Scientists" is more than a decade old and only has 46 signers.
  2. The Heidelberg Appeal actually does not say anything about global warming.
  3. Most of the signers of the Leipzig Declarations are non-scientists or lack credentials in the specific field of climate research.
  4. Many of the signers of the Oregon Petition are also non-scientists or lack relevant scientific backgrounds.

Discussion of some of the points

Global warming and carbon dioxide

One argument against global warming questions the contention that rising levels of carbon dioxide and other greenhouse gases (GHGs) correlate with—and thus have caused—global warming. However, this amounts to questioning a strawman, since the assertion that GHGs cause global warming is not based on correlation at all: see attribution of recent climate change.

Missing image
420,000 years of ice core data from Vostok, Antarctica research station (present time at the left).
  • Correlation is not causation. Indeed, studies of ice age temperature variations show carbon dioxide levels increasing after warming rather than before. [10] (, [11] ( This however assumes that current climate change can be expected to be like past climate change. This is unlikely: past (ice age) variations are timed by astronomical forcing; the current variations, of whatever size, are timed by anthropogenic releases of CO2.
  • Most warming during the past century took place before most carbon dioxide had been released.
  • Between 1940 and 1970, global temperatures went down even though carbon-dioxide levels went up.

As noted above, climate models are only able to simulate the temperature record of the past century when GHG forcing is included, which some insist strongly points to the importance of GHGs, as does attribution of recent climate change.

Urban heat islands

Main article: Urban heat island

Another argument from the global warming skeptics, is that records of temperature change are wrong because temperature monitoring stations are located in urban areas and as such the measurements they take are distorted by the heat of the city (from cars, house heating etc).

A study in Nature in November 2004 attempts to correct for this, by comparing tempature readings taken on calm nights with those taken on windy nights. If the urban heat island theory is correct then instruments should have recorded a bigger temperature rise for calm nights than for windy ones—because wind blows excess heat away from cities and away from the measuring instruments. There was no difference between the calm and windy nights. [12] (

Skeptics remain unconvinced. Fred Singer of the SEPP said of the study "Many people have tried to correct for the urban heat island effect... I'm not sure David Parker has succeeded, but we admire his ingenuity."

Global warming and solar activity

Main article: Solar variation theory

Another point of controversy regarding anthropogenic global warming is the investigation of temperature correlations with the solar variation. This subject is a point of controversy between supporters and opponents of anthropogenic global warming.

Beneficial or detrimental

There is also disagreement on whether the effects of global warming will be beneficial or detrimental. Many researchers predict disastrous consequences for a warming of 1.5 to 7 degrees Celsius. The UN's Intergovernmental Panel on Climate Change (IPCC) predicts such a warming is likely within the 21st century, unless severe measures are taken (see Kyoto Protocol).

Other researchers feel that up to 1.5 degrees Celsius of warming would increase crop yields and stabilize weather. Many of these doubt a larger warming is likely. In response, some advocates of strong early measures (well beyond Kyoto) note that the belief in beneficial effects and the doubt that a large warming is possible should be independent if these conclusions were in fact neutrally derived from scientific research.

An unstable world

New findings have suggested that the earth's climate system is inherently unstable, and that global warming could thus precipitate non-linear sudden climate shifts, as have been discovered to have occurred within the earth's past. Ocean circulation, believed to be the key to such climate shifts, has been observed to be slowing, causing alarm among oceanographers. Some scientists fear that the Gulf Stream, which conveys warm water from the Caribbean Sea across the Atlantic Ocean and is partly responsible for the relative mildness of northern Europe's climate (though other factors also predominate: [13] (, could be reduced or stopped altogether by the decreased salt content of sea water resulting from global warming. This could cause temperatures in northern Europe to drop.

The US National Academy of Sciences issued a report on this phenomenon in 2002, titled Abrupt Climate Change - Inevitable Surprises. [14] ( "It is important not to be fatalistic about the threats posed by abrupt climate change," it stated. "Societies have faced both gradual and abrupt climate changes for millennia and have learned to adapt through various mechanisms, such as moving indoors, developing irrigation for crops, and migrating away from inhospitable regions. Nevertheless, because climate change will likely continue in the coming decades, denying the likelihood or downplaying the relevance of past abrupt events could be costly."

Kyoto Protocol

Advocates of the global warming hypothesis who predict adverse consequences from as little as 1.5 degrees Celsius of warming nearly all support the Kyoto Protocol as a countermeasure. Details of the agreement are in the article about the Kyoto Protocol, including both the pollution and fiscal requirements.

Paradigms present

The evaluation of importance of influences is affected by several paradigms being used, with some specialties using some concepts as having more influence than others. Many of the apparent contradictions can be resolved by noting that different specialties may use different time and amplitude scales for various influences and concepts.

  • The climate system has been in a steady state (e.g., during the Holocene, i.e., the last 10 kyr).
  • The climate system has had large variations (canonically, ice ages).
  • The climate system is dominated by internal processes.
  • Large influences tend to have large effects.
  • The climate response to forcing is largely linear.
  • Internal processes exist which amplify otherwise small influences.
  • Conditions now are significantly different from those in the past.

See also

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