Fourth Assessment Report of the IPCC

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With coal, gas and oil we heat up the greenhouse effect.
Source: tomas /

In 2007, the Intergovernmental Panel on Climate Change (IPCC) published its Fourth Assessment Report. The conclusion: Warming of the climate system is unequivocal.

In its Fourth Assessment Report, the IPPC declared the following:

  • Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide (laughing gas) have increased markedly as a result of human activities since 1750. Global increases in carbon dioxide concentrations are due primarily to fossil fuel use, whereas the observed increase in methane and nitrous oxide is predominantly due to agriculture.
  • Atmospheric concentrations of greenhouse gases in 2005 exceed by far the natural range determined by ice cores of the last 650,000 years.
  • With the better understanding of the anthropogenic influence on the climate that was conveyed in the Third Assessment Report, it has been widely acknowledged that the sum effect of human activities on the globe since 1750 was a warming of the climate.
  • The signs of global warming are unequivocal, as proven by the observed increase in global mean air and ocean temperatures, the widespread melting of snow and ice, and the rise in global mean sea level.
  • The linear warming trend over the 100-year period of 1906 – 2005 is about 0.74 degree Celsius. Eleven of the years from 1995 to 2006 were the warmest since instrumental measurement and recording of global surface mean temperature began (1850).
  • Mountain glaciers and snow cover have generally retreated on both the Northern and Southern hemisphere. The Greenland ice sheet shows significant ice shrinkage due to melting processes.
  • The average temperatures in the Arctic have risen at a rate nearly double that of the global mean in the past 100 years. Satellite data since 1978 provides evidence that the average annual expansion of Arctic Sea ice has declined by about 2.7 percent per decade. Shrinkage in summer was as high as around 7.4 percent per decade.
  • In the 1905 – 2005 period observations confirm significant increases in precipitation in eastern regions of North and South America, in northern Europe, and in northern and central Asia. In contrast, southern Africa, the Mediterranean region, the Sahel, and certain parts of southern Asia became drier.
  • In the past 50 years the frequency of cold days, cold nights and frosts has decreased, whereas the incidence of hot days, hot nights, and heat waves was greater. Since the 1970s scientists have observed- particularly in tropical and subtropical zones- more intensive and longer-lasting periods of drought affecting larger areas.
  • Most of the increase in global mean temperatures since the middle of the 20th century is very likely (which means its likelihood is more than 90 percent) caused by man-made greenhouse gases in the atmosphere.
  • Consistently high or higher greenhouse gas emissions than current levels would cause warming and bring about many changes in the global climate system in the course of the 21st century. These changes are very likely to be greater than those observed during the 20th century.
  • Based on various emission scenarios (projected development of greenhouse gas emissions over time) scientists applied several climate models to simulate the possible climate changes in this century. The findings in the Fourth Assessment Report are founded on the results of 23 different climate models based on 6 emission scenarios. The projected changes in global mean temperature up until 2090 – 2099 are significant as compared to 1980 – 1999. They range from 1.8 degree Celsius in the lowest emission scenario, to 4 degree Celsius in the highest scenario (best estimates). The correspondent uncertainty ranges (the likely uncertainty intervals of best estimates) are even greater. Even if atmospheric concentrations of greenhouse gases were contained at the same level as in 2000, the climate models showed an increase in global mean temperature of about 0.6 degree Celsius by the end of the century.
  • The anthropogenic warming and increase in sea level will occur for centuries because of the time scales that are associated with processes and feedbacks in the climate system - even if greenhouse gas concentrations are stabilised