IPCC Fourth Assessment Report

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Template:IPCC The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) is the fourth in a series of reports on climate change. It concludes that global warming is happening, and is very likely caused by human emissions of greenhouse gases.

The Working Group I Summary for Policymakers report was published on 2 February, 2007; the full WGI report will be published in a few months. Working Group II and Working Group III reports are scheduled for early April and early May, respectively. The AR4 Synthesis Report (SYR) is expected to be finalised during the last quarter of 2007. Author lists and a chapter outline of the WGI report are available.[1]

The AR4 is expected to include, apart from updated science, a greater focus on uncertainty, risk concepts and regional integration.

Contents

Working Group I report

Climate Change 2007: The Physical Science Basis, the report of Working Group I, "assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change". The use of the phrase "drivers of climate change" represents increased certainty regarding the effects of human activity.

The report was produced by around 600 authors from 40 countries, and reviewed by over 620 experts and governments. Before being accepted, the summary was reviewed line-by-line by representatives from 113 governments during the 10th Session of Working Group I,[2], which took place in Paris, France, between 29 January and 1 February 2007.

The key conclusions were that[3]:

  • It is "unequivocal" that global warming is occurring
  • The probability that this is caused by natural climatic processes is less than 5%
  • The probability that this is caused by human emissions of greenhouse gases is over 90%

As a result it is predicted that, during the 21st century:

  • Surface air warming in the 21st century:
    • Best estimate for a "low scenario"[4] is 1.8 �C with a likely range of 1.1 to 2.9 �C (3.2 �F with a likely range of 2.0 to 5.2 �F)
    • Best estimate for a "high scenario"[5] is 4.0 �C with a likely range of 2.4 to 6.4 �C (7.2 �F with a likely range of 4.3 to 11.5 �F)
  • Based on a model that excludes ice sheet flow due to a lack of basis in published literature,[6] it is estimated that sea level rise will be:
    • in a low scenario[4] 18 to 38 cm (7 to 15 inches)
    • in a high scenario[5] 26 to 59 cm (10 to 23 inches)
  • It is more than 90% certain that there will be frequent warm spells, heat waves and heavy rainfall
  • It is more than 66% certain that there will be an increase in droughts, tropical cyclones and extreme high tides.

Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium, due to the timescales required for removal of this gas from the atmosphere.

Reaction

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." [7]

After the report's release The Guardian reported that the American Enterprise Institute, who the newspaper calls "an ExxonMobil-funded think tank with close links to the Bush administration", had offered several scientists $10,000(US) each to write articles disputing the IPCC's conclusions.[8]

See also

References

  1. ^ WG I Fourth Assessment Report (AR4)
  2. ^ IPCC adopts major assessment of climate change science
  3. ^ Climate Change 2007: The Physical Science Basis. Summary for Policymakers
  4. ^ a b "... a convergent world with the same global population, that peaks in mid-century and declines thereafter, ... but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives."
  5. ^ a b "... a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. 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. ... technological emphasis: fossil intensive"
  6. ^ This contrasts with the TAR, which included these ice dynamics, and had a higher top end sea level rise estimate. 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."
  7. ^ [1] UK scientists' IPCC reaction by the BBC
  8. ^ Guardian Unlimited: Scientists offered cash to dispute climate study, February 2, 2007

External links


References

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