IPCC 2007 Report

views updated

IPCC 2007 Report


The Intergovernmental Panel on Climate Change (IPCC) is a group of scientists, economists, and government officials from member states of the United Nations. The IPCC was formed to provide government decision-makers, scientists, and interested citizens with objective scientific information about climate change. The panel does not recommend specific actions that governments should take to respond to climate change; its task is, in its own words, to strictly assess “the latest scientific, technical and socio-economic literature produced worldwide relevant to the understanding of the risk of human-induced climate change, its observed and projected impacts and options for adaptation and mitigation.” The IPCC has released four sets of Assessment Reports (1990, 1995, 2001, 2007) summarizing the developing state of climate science.

The 2007 Fourth Assessment Report (AR4) built on advances in climate science since 2000 and used more sophisticated computer-generated climate models than its predecessor. It was a landmark in communicating the scientific consensus on climate change to the public and to governments. Its announcement that global warming is “unequivocal” made headlines around the world and has altered government policies, media coverage, and public concerns.

The most persistent scientific criticism of the report has been that it was too conservative, that is, projected a too-rosy picture of likely future climate change. The IPCC was also accused of moderating its warnings in response to pressure from the governments of India, China, and the United States. Such pressure could be applied because the IPCC’s assessment reports must be approved by all member governments before they can be released.

Historical Background and Scientific Foundations

The IPCC is the world’s leading authority on climate change. It was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP). Since that time, it has produced a number of publications, but the most influential are its Assessment Reports. The Fourth Assessment Report (AR4) was released in stages throughout 2007.

About 2,500 authors participated in writing AR4, all scientists or economists. No research was carried out especially for the report; instead, scientists reviewed the existing peer-reviewed scientific literature on climate (up to the end of 2005) and brought together its most important findings and uncertainties into a single, logically organized book. Peer review is review of scientific papers by fellow experts, before publication. Peer reviewers look for faults in each submitted scientific paper or article; faults may be corrected by the author or may lead to the rejection of the paper. In modern science, peer review is used by all technical publications to assure the greatest possible accuracy for all claims.

AR4 consists of three thick volumes, each dedicated to a major aspect of climate science. There is also a fourth, slimmer report that synthesizes (summarizes the key points of) the three main reports. The three volumes are The Physical Science Basis, Impacts, Adaptation and Vulnerability, and Mitigation of Climate Change. Each volume is prefaced by a “Summary for Policymakers” that was released in advance of the volume. For example, the “Physical Science Basis Summary for Policymakers,” the first part of the AR4 to be released, became available on February 2, 2007, but the main body of the Physical Science Basis report did not become available until about a month later. The Synthesis Report, the final part of AR4, was not released until November 2007.


ANTHROPOGENIC: Made by humans or resulting from human activities.

CLIMATE MODEL: A quantitative method of simulating the interactions of the atmosphere, oceans, land surface, and ice. Models can range from relatively simple to quite comprehensive.

GREENHOUSE GAS: A gas whose accumulation in the atmosphere increases heat retention.

ICE SHEET: Glacial ice that covers at least 19,500 square mi (50,000 square km) of land and that flows in all directions, covering and obscuring the landscape below it.

INDUSTRIAL REVOLUTION: The period, beginning about the middle of the eighteenth century, during which humans began to use steam engines as a major source of power.

PEER REVIEW: The standard process in science for reducing the chances that faulty or fraudulent claims will be published in scientific journals. Before publication of an article, scientists with expertise in the article’s subject area review the manuscript, usually anonymously, and make criticisms that may lead to revision or rejection of the article.

PERMAFROST: Perennially frozen ground that occurs wherever the temperature remains below 0°C for several years.

The main conclusions of AR4 are listed in its “Summaries for Policymakers” and in its Synthesis Report. The following is a selection of those conclusions:

  1. Warming of the global climate is now unequivocal, that is, essentially certain. Effects of warming include overall warmer climate, rising sea level, decreased snow and ice, changed precipitation patterns in many regions, and more frequent extreme weather events such as heat waves and storms.
  2. Natural systems on all continents are being affected by climate changes, particularly warming. Glacial lakes, melting permafrost, and changes to some Arctic and Antarctic ecosystems have been observed, as have changes in hydrological (water-flow) systems due to increased and earlier spring season melting of glaciers and snowpacks. In some lakes, increased layering of waters due to increased surface warmth has been observed. Spring arrives earlier and plant and animal ranges have shifted to cooler regions (more northerly latitudes, higher altitudes).
  3. Global greenhouse-gas emissions by humans have increased the concentrations of those gases in the atmosphere. In particular, global atmospheric carbon dioxide (CO2) and nitrous oxide (N2O) now far exceed pre-Industrial Revolution (pre-1750) values. Overall, greenhouse-gas emissions have increased by 70% from 1970 to 2004. Atmospheric concentrations of CO2, because of human emissions, now exceed any natural extreme seen for at least 650,000 years.
  4. Most of the increase in global average temperature since the middle of the twentieth century is, with greater than 90% probability, due to human-caused greenhouse-gas emissions. Humans have influenced other aspects of climate in addition to warming.
  5. The magnitude of future changes will depend on how large anthropogenic greenhouse-gas emissions continue to be. However, some increases in sea level (due to melting glacial ice and thermal expansion of warming sea waters) and global temperature are bound to continue for centuries, even if greenhouse emissions are stabilized, because it will take that long for the world climate system to get into balance or equilibrium with the changes humans have already made.
  6. Extreme weather events will occur more often and be more intense; sea levels have already risen and will continue to rise. These changes will have mostly negative affects on both human and natural systems. Sudden and irreversible changes may also occur. There is medium confidence that temperature rises exceeding 2.6–4.5°F (1.4–2.5°C) relative to global temperature during 1980 to 1999 will put 20–30% of all plant and animal species at increased risk of extinction; with warming of 6.3°F (3.5°C) or higher, extinction of 40–70% of all species is suggested by some projections.
  7. Sea-level rise over century timescales could be much greater than that predicted for the near term (the rest of this century). Ice-loss processes observed too recently to be taken into account by AR4, the Synthesis Report notes, “could increase the rate of ice loss.” This refers especially to the speedup of glaciers flowing into the sea in Greenland and the West Antarctic Peninsula.
  8. Both the impacts of climate change on human society and the ability to adapt to them are unevenly distributed. In general, poor nations are located where they will experience more severe impacts, and are more poorly equipped to adapt to such impacts.
  9. There are many ways to reduce greenhouse-gas emissions that would actually be profitable (have “negative costs”). Increased energy end-use efficiency is the largest single area of opportunity. Although AR4 carefully avoids saying that governments should respond in any particular way, it does say that “delayed emission reductions significantly constrain the opportunities to achieve lower stabilization levels and increase the risk of more severe climate change impacts.”

Impacts and Issues

Because AR4’s three book-length main sections are large, somewhat technical, and were released weeks or months after their “Summaries for Policymakers,” the summaries have been the most-read and most-reported-on parts of AR4. The “Summary for Policymakers,” of the Physical Science Basis report, the first section of AR4 to be released, had the greatest political and public impact. Its release on February 2, 2007, was widely reported and discussed in the world media. The New York Times reported the following day that “Science Panel Calls Global Warming ‘Unequivoca’” and called AR4 “a grim and powerful assessment of the future of the planet.” The same day, the Times of London, ran the headline “New Fears on Climate Raise Heat on Leaders” and called AR4 the IPCC’s “bleakest and most confident assessment yet of the science behind global warming.” The White House held a press briefing on April 6, 2007 to discuss AR4 with reporters, and although the George W. Bush administration had often downplayed or even deleted references to climate change in official U.S. government documents, the administration-appointed scientists at the press conference praised AR4 and did not dispute its claims.

Most striking to journalists and commentators was the summary’s straightforward proclamation that there was no longer any significant scientific debate on the reality of global climate change, which it now said was “unequivocal” (virtually certain). Also newsworthy was its statement that human beings are causing the warming: “Most of the observed increase in global average temperatures since the mid-twentieth century is very likely [more than 90% likely] due to the observed increase in anthropogenic greenhouse-gas concentrations.”

After decades, the global scientific community had spoken with a single voice. In fact, scientific consensus on the reality and human-caused nature of global warming was already well developed by the late 1990s, but the 2001 Assessment Report of the IPCC had not used such strong language as it did with the 2007 report. The consensus was not new, but the strong language was. Now that global warming was deemed unequivocal, it had become undeniable that very few scientists still disagreed with the main points of the climate consensus. Uncertainties lingered and would always linger to some degree, especially in predictions of future change, but they had been decreased by improved science to a level where inaction no longer seemed reasonable.

AR4 was particularly credible because the IPCC’s reports are, if anything, biased toward being too conser-


The scientific evidence that global warming is occurring is undeniable. Because the answer is critical to shaping future policy, the key question for the Intergovernmental Panel on Climate Change (IPCC) is whether the cause is natural or caused by anthropogenic (human) activity. On this point, the authoritative 2007 IPCC report reflecting strong scientific consensus is clear.

“The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that it is not due to known natural causes alone…. It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica.”

Moreover, the 2007 IPCC report shows that, in addition to future perils, human driven climate change already impacts everyday life: “Temperatures of the most extreme hot nights, cold nights and cold days are likely to have increased due to anthropogenic forcing. It is more likely than not that anthropogenic forcing has increased the risk of heat waves.”

SOURCE: Solomon, S., et al, eds. “IPCC, 2007: Summary for Policymakers.” In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

vative or over-careful. All contributing governments must approve the final report for release, including some historically unfriendly to the concept of global warming and to proposals to mitigate greenhouse-gas emissions, such as the governments of Australia, the United States, China, Russia, and Saudi Arabia. AR4 was therefore no product of “environmentalist wacks,” in the phrase of prominent U.S. greenhouse denialist Rush Limbaugh. It was viewed as sober, minimalist, and cautious—perhaps even too cautious. Many scientists argued that the IPCC’s politicized approval process had led to a document that understated climate dangers. Media reported how the United States, Saudi Arabia, and China, all of whom oppose mandatory caps on their greenhouse emissions, had potentially alarming phrases about climate change struck from the final version of the report. The IPCC’s process, being slow, also has a tendency to leave out cutting-edge research, such as the 2006 discoveries that the Greenland ice cap is melting much faster than anyone had known or predicted. In its November 2007 synthesis report, the IPCC acknowledged that such new knowledge had not been fully included in ice sheet models assessed in AR4.

AR4 is the last IPCC report until approximately 2012. Until that time, it will be referenced in almost every debate about climate change. It is a compendious, authoritative treatment of the available science of climate change on which virtually all governments and the great majority of scientists have agreed.

The IPCC shared the Nobel Peace Prize for 2007 with climate-change activist and former U.S. Vice President Al Gore. Gore and the IPCC were acknowledged for their work in bringing awareness of climate change to people throughout the world.

See Also Climate Change; Global Warming; Hurricanes; Intergovernmental Panel on Climate Change; Sea Level Rise



Metz, B., et al, eds. Climate Change 2007: Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Parry, M. L., et al, eds. Climate Change 2007: Impacts, Adaptation and Vulnerability: Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Solomon, S., et al, eds. Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Weart, Spencer. The Discovery of Global Warming. Cambridge, MA: Harvard University Press, 2004.


Biello, David. “Conservative Climate: Consensus Document May Understate the Climate Change Problem.” Scientific American (March 18, 2007).

“A Clear Direction” (editorial). Nature 447 (2007): 115.

Dean, Cornelia. “Even Before Its Release, World Climate Report Is Criticized as Too Optimistic.” New York Times (February 2, 2007).

Eilperin, Juliet. “U.S., China Got Climate Warnings Toned Down.” Washington Post (April 7, 2007).

Gibbs, Walter. “Gore and U.N. Panel Win Peace Prize for Climate Work.” New York Times (October 13, 2007).

Oppenheimer, Michael, et al. “The Limits of Consensus.” Science 317 (2007): 150–151.

Oreskes, Naomi. “The Scientific Consensus on Climate Change.” Science306 (2004): 1686.

“Rising to the Climate Challenge.” Nature 449(2007): 755.

Rosenthal, Elisabeth, and Andrew C. Revkin. “Science Panel Calls Global Warming ‘Unequivocal.’” New York Times (February 3, 2007).

Web Sites

Rushlimbaugh.com. “Record Cold Raises No Questions; Polar Bear Photo a Fraud.” http://www.rushlimbaugh.com/home/daily/site_020507/content/0205071.guest.html(accessed March 29, 2008).

United Nations Intergovernmental Panel on Climate Change. “IPCC Reports.” http://www.ipcc.ch/ipccreports/assessments-reports.htm (accessed March 29, 2008).

Larry Gilman

About this article

IPCC 2007 Report

Updated About encyclopedia.com content Print Article