UN says man's global warming impact lower than thought
mongabay.com
December 11, 2006



When it is released in February 2007, the UN Intergovernmental Panel on Climate Change (IPCC) will report that man's impact on global climate is less than previously believed according to a story published in the Sunday edition of the UK-based Telegraph.




The Telegraph says that the report will reduce its estimate of man's role in global warming by 25 percent. However, the IPCC will still project global temperatures to climb by 4.5 C during the next century and rising sea levels, albeit by half the amount -- 17 inches instead of 34 inches by 2100 -- forecast by the IPCC's 2001 report. It will also note that atmospheric carbon dioxide levels have continued to climb over the past five years but that the overall human effect on global warming since the industrial revolution has been dampened by cooling caused by particulate matter and aerosol sprays, which accumulate in the upper atmosphere and reflect heat from the sun.

The UN will say the findings are the result of more refined estimates based on new data rather than "a reduction in the risk posed by global warming."

The reduced anthropologic impact on climate change is expected to produce ammunition for newly-emboldened global warming skeptics who are increasingly out-numbered in the field of public opinion. In recent years, there has been a shift in general public perception on climate change, with more people believing that human-fueled carbon dioxide emissions are warming the planet. Intense storms like Hurricane Katrina, higher temperatures including deadly heat waves across Europe and the United States, melting ice in the Arctic and Antarctica, and evidence of rising sea levels have bolstered support for the contention that climate change is a real threat. Further, a series of prominent reports have said that climate change could carry massive costs. Most recently, on October 30, 2006, a report released by the British government warned that the economic cost of climate change could be staggering, causing worldwide a recession rivaling that of the Great Depression.



Atmospheric CO2 levels have climbed by more than 35 percent since the beginning of the industrial revolution. Fossil fuel combustion, which releases carbon dioxide into the atmosphere, and land-use change, including deforestation, is blamed for the rise. Roughly 75-80 percent of anthropogenic carbon dioxide results from fossil fuel burning, while about 20-25 percent is produced by deforestation. The United States, the world's largest economy and consumer of energy, produces about 24% of global carbon dioxide emissions.

Scientists believe rising levels of carbon dioxide and other greenhouse gases are causing Earth's atmosphere to warm. Research released earlier this year by NASA, WMO, and the National Academy of Sciences found that 2005 was the warmest year in at least the 400 years, and possibly much longer. The WMO says that carbon dioxide has accounted for 90 percent of warming over the past decade.

Last week a study published in the journal Science (Pagani et al.) said that future climate change could resemble an episode of rapid warming that occurred some 55 million years ago. During that period, known as the Paleocene-Eocene Thermal Maximum (PETM), levels of carbon dioxide spike, causing temperatures to jump. The researchers said that doubling of CO2 concentrations, which is expected tp occur around mid-century due to fossil fuel consumption, can raise global temperatures by at least 4 ºF (2.2 ºC) and possibly by as much as 10 ºF (5.6 ºC).

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess the "risk of human-induced climate change". Its last climate assessment ("IPCC Third Assessment Report: Climate Change 2001") was published in 2001. The next (IPCC Fourth Assessment Report: Climate Change 2001) is scheduled to be published in February 2007.




This article uses information from the Sunday Telegraph and previous mongabay.com articles.



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CITATION:
mongabay.com (December 10, 2006).

UN says man's global warming impact lower than thought.

http://news.mongabay.com/2006/1210-un.html