Climate Change , the Fourth Assessment Report AR4 of the United Nations Intergovernmental Panel on Climate Change IPCC , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change , its potential effects, and options for adaptation and mitigation. The report is the largest and most detailed summary of the climate change situation ever undertaken, produced by thousands of authors, editors, and reviewers from dozens of countries, citing over 6, peer-reviewed scientific studies. The headline findings of the report were: "warming of the climate system is unequivocal", and "most of the observed increase in global average temperatures since the midth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. This section of the report, Climate Change The Physical Science Basis , assessed current scientific knowledge of "the natural and human drivers of climate change" as well as observed changes in climate. It looked at the ability of science to attribute changes to different causes, and made projections of future climate change. It was produced by authors lead authors, 26 review editors, and contributing authors from 40 countries, then reviewed by over expert reviewers.
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Climate Change , the Fourth Assessment Report AR4 of the United Nations Intergovernmental Panel on Climate Change IPCC , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change , its potential effects, and options for adaptation and mitigation.
The report is the largest and most detailed summary of the climate change situation ever undertaken, produced by thousands of authors, editors, and reviewers from dozens of countries, citing over 6, peer-reviewed scientific studies.
The headline findings of the report were: "warming of the climate system is unequivocal", and "most of the observed increase in global average temperatures since the midth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.
This section of the report, Climate Change The Physical Science Basis , assessed current scientific knowledge of "the natural and human drivers of climate change" as well as observed changes in climate. It looked at the ability of science to attribute changes to different causes, and made projections of future climate change. It was produced by authors lead authors, 26 review editors, and contributing authors from 40 countries, then reviewed by over expert reviewers.
More than 6, peer-reviewed publications were cited. Before being approved, the summary was reviewed line by line by representatives of governments during the 10th session of WGI, in January to February The report notes many observed changes in the Earth's climate including atmospheric composition, global average temperatures, ocean conditions, and other climate changes. Carbon dioxide , methane , and nitrous oxide are all long-lived greenhouse gases.
Cold days, cold nights, and frost events have become less frequent. Hot days, hot nights, and heat waves have become more frequent. The SPM documents increases in wind intensity, decline of permafrost coverage, and increases of both drought and heavy precipitation events. Table SPM-2 lists recent trends along with certainty levels for the trend having actually occurred, for a human contribution to the trend, and for the trend occurring in the future.
In relation to changes including increased hurricane intensity where the certainty of a human contribution is stated as "more likely than not" footnote f to table SPM-2 notes "Magnitude of anthropogenic contributions not assessed. Attribution for these phenomena based on expert judgment rather than formal attribution studies. The report shows in detail the individual warming contributions positive forcing of carbon dioxide, methane, nitrous oxide, halocarbons , other human warming factors, and the warming effects of changes in solar activity.
Also shown are the cooling effects negative forcing of aerosols , land-use changes, and other human activities. All values are shown as a change from pre-industrial conditions. Climate sensitivity is defined as the amount of global average surface warming following a doubling of carbon dioxide concentrations.
Model projections are made based on an analysis of various computer climate models running within the different scenarios that were established in in the Special Report on Emissions Scenarios the "SRES scenarios". As a result, predictions for the 21st century are as shown below. Scenario-specific projections are based on analysis of multiple runs by multiple climate models, using the various SRES Scenarios. There are six families of SRES scenarios, and AR4 provides projected temperature and sea level rises excluding future rapid dynamical changes in ice flow for each scenario family.
In the weeks before publication of the first report, controversy broke out about the report's projections of sea-level change, which in the new report was estimated at less than previous estimates. The now-published text gives a warning that the new estimation of sea-level could be too low: "Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise.
Lord Rees , the president of the Royal Society , said, "This report makes it clear, more convincingly than ever before, that human actions are writ large on the changes we are seeing, and will see, to our climate. The IPCC strongly emphasises that substantial climate change is inevitable, and we will have to adapt to this.
This should compel all of us — world leaders, businesses and individuals — towards action rather than the paralysis of fear. We need both to reduce our emissions of greenhouse gases and to prepare for the impacts of climate change. Those who would claim otherwise can no longer use science as a basis for their argument.
Energy Secretary Samuel Bodman told a news conference that the report was "sound science" and "As the president has said, and this report makes clear, human activity is contributing to changes in our earth's climate and that issue is no longer up for debate. The 46 countries included the European Union nations, but notably did not include the United States , China , Russia , and India , the top four emitters of greenhouse gases.
The full report was released September 18, WGII states that "evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.
With a high confidence about an 8 in 10 chance to be correct WGII asserts that climate change has resulted in:. With a very high confidence about a 9 in 10 chance to be correct WGII asserts that climate change is affecting terrestrial biological systems in that:. WGII also states that the ocean has become more acidic because it has absorbed human-caused carbon dioxide.
Ocean pH has dropped by 0. WGII acknowledges some of the difficulties of attributing specific changes to human-caused global warming, stating that "Limitations and gaps prevent more complete attribution of the causes of observed system responses to anthropogenic warming.
WGII describes some of what might be expected in the coming century, based on studies and model projections. The original draft read: "However, adaptation alone is not expected to cope with all the projected effects of climate change, and especially not over the long run as most impacts increase in magnitude. Mitigation measures will therefore also be required. China objected to wording that said "based on observed evidence, there is very high confidence that many natural systems, on all continents and in most oceans, are being affected by regional climate changes, particularly temperature increases.
The IPCC convened in Bangkok on April 30 to start discussions on the draft Summary, with the participation of over scientists and experts from about countries. One of the key debates concerned a proposal to limit concentrations of greenhouse gases in the atmosphere to between parts per million and parts per million to avoid dangerous climate change , with pressure from developing countries to raise the lower limit.
Despite this, the figures from the original proposal were incorporated into the Summary for Policymakers. The WG III report analyses mitigation options for the main sectors in the near-term, addressing also cross-sectorial matters such as synergies, co-benefits, and trade-offs. It also provides information on long-term mitigation strategies for various stabilization levels, paying special attention to implications of different short-term strategies for achieving long-term goals. The Summary for Policymakers concludes that there was a high level of agreement and much evidence that 'there is substantial economic potential for the mitigation of global greenhouse gas emissions over the coming decades, that could offset the projected growth of global emissions or reduce emissions below current levels',  taking into account financial and social costs and benefits.
The IPCC estimates that stabilizing atmospheric greenhouse gases at between ppm CO 2 equivalent would result in a reduction of average annual GDP growth rates of less than 0. Stabilizing at to ppm would reduce average annual GDP growth rates by 0. They also concluded that it is often more cost effective to invest in end-use energy efficiency improvement than in increasing energy supply.
They also warn that higher oil prices might lead to the exploitation of high-carbon alternatives such as oil sands , oil shales , heavy oils , and synthetic fuels from coal and gas, leading to increasing emissions, unless carbon capture and storage technologies are employed.
In the transport sector there was a medium level of agreement and evidence that the multiple mitigation options may be counteracted by increased use, and that there were many barriers and a lack of government policy frameworks.
There was high agreement and much evidence that, despite many barriers particularly in the developing countries , new and existing buildings could reduce emissions considerably, and that this would also provide other benefits in terms of improved air quality, social welfare and energy security. The IPCC reported that the effectiveness of mitigation efforts over the next two or three decades would have a large impact on the ability to stabilize atmospheric greenhouse gases at lower levels, and that the lower the ultimate stabilization levels, the more quickly emissions would need to peak and decline.
There was high agreement and much evidence that stabilization could be achieved by using currently available technologies, provided appropriate and effective incentives were put in place for their development, acquisition, deployment and diffusion, and that barriers were removed.
Among the measures that might be used, there was high agreement and much evidence that policies that put a price on the cost of carbon emissions could provide incentives for consumers and producers. A draft version of the Synthesis Report, said to be subject to final copyedit, was published on 16 November The Synthesis Report goes one step further [than the first three Climate Change Working Group Reports]: it is the decisive effort to integrate and compact this wealth of information into a readable and concise document explicitly targeted to the policymakers.
The Synthesis Report also brings in relevant parts some material contained in the full Working Group Reports over and above what is included in the Summary for Policymakers in these three Reports. It is designed to be a powerful, scientifically authoritative document of high policy relevance, which will be a major contribution to the discussions at the 13th Conference of the Parties in Bali during December The six topics  addressed in the Synthesis Report are:.
The SPM states that "Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.
The Fourth Assessment Report has been the subject of criticism. Skeptics of anthropogenic global warming contend that their claims are not sufficiently incorporated in the report. Others regard the IPCC as too conservative in its estimates of potential harm from climate change.
The report has also been criticized for inclusion of an erroneous date for the projected demise of the Himalayan glaciers.
Related to the subject of global warming in general, the IPCC Fourth Assessment Report has been discussed by various bodies such as government officials, special interest groups and scientific organizations; see the article " Politics of global warming " for a thorough discussion of the politics surrounding the phenomenon, and the positions of the various parties involved. Additional reports and documents can be found at the IPCC's documents web page.
From Wikipedia, the free encyclopedia. See also: Mitigation of global warming. Energy portal. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income.
The report states that recent observations suggest that ice flow dynamics could lead to additional rise: " Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise.
Understanding of these processes is limited and there is no consensus on their magnitude. BBC News. Monterey County Herald. Archived from the original on Or pdf Archived November 25, , at the Wayback Machine. The Washington Post. Retrieved September Archived from the original PDF on New York Times. Retrieved 28 February Global warming.
Attribution of recent climate change Effects of global warming Climate change mitigation Climate change adaptation By country and region. Attribution of recent climate change Greenhouse effect Scientific consensus on climate change. Greenhouse gases Fossil fuel Deforestation and climate change Land use, land-use change, and forestry.
Effects and issues. Abrupt climate change Anoxic event Arctic methane emissions Drought Ocean acidification Ozone depletion Physical impacts Retreat of glaciers since Runaway climate change Sea level rise Season creep Shutdown of thermohaline circulation. Climate change and ecosystems Effects on plant biodiversity Effects on marine life Effects on marine mammals Effects on terrestrial animals Extinction risk from global warming Forest dieback. Climate change and agriculture Climate change and ecosystems Climate change and gender Climate change and poverty Economics of global warming Effects on health Effects on humans Human rights Environmental migrant Fisheries and climate change Industry and society.
Carbon tax Low-carbon economy Emissions trading Carbon credit Carbon offset. Sustainable energy Low-carbon energy Renewable energy Nuclear power Carbon capture and storage Energy transition. Individual action on climate change Carbon neutrality.
IPCC Fourth Assessment Report
IPCC Fourth Assessment Report