Monday 4 February 2008

IPCC 4th Assessment Report

The Intergovernmental Panel on Climate Change (IPCC) published its Fourth Assessment in 2007. The main conclusions drawn were as follows.

  • Warming of the climate system is unequivocal.
  • Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (human) greenhouse gas concentrations.
  • Anthropogenic warming and sea level rise will continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized, although the likely amount of temperature and sea level rise varies greatly depending on the fossil fuel burning intensity of human activity during the next century.
  • The probability that this is caused by natural climatic processes alone is less than 5%.
  • World temperatures could rise by between 1.1 and 6.4 °C during the 21st century.
  • Sea levels will probably rise by 18 to 59 cm.
  • There is a confidence level of more than 90% that there will be more frequent warm spells, heat waves and heavy rainfall.
  • There is a confidence level of more than 66% 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.
  • Global atmospheric concentrations ofcarbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values over the past 650,000 years.


Some critics have contended that the IPCC reports tend to underestimate dangers, understate risks, and report only the "lowest common denominator" findings (McKibben, 2007). It may already be out of date and omits recent observations and factors contributing to global warming, such as the release of greenhouse gases from thawing tundra. Some other studies estimate that in 2100 sea levels could be 0.5–1.4 m above 1990 levels

Fourth Assessment Report, 2007. Intergovernmental Panel on Climate Change [online]. Available at: http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf [04.02.08].

McKibben, B., 2007. Warning on Warming. The New York Review of Books [online]. 54(4). Available at: http://www.nybooks.com/articles/19981 [03.02.08].

Sea level rise 'under-estimated'. 2006 [online]. Available at: http://news.bbc.co.uk/1/hi/sci/tech/6179409.stm [04.02.08].

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