IPCC AR4 – Summary

In this post I’m going to sum up the most important statements of the IPCC AR4 report. The reason for doing this is to have a easy to scan source for myself and everyone interested in this topic. I think it’s one of the great advantages of a blog system to easily share material you otherwise would only produce for yourself. And so other persons may benefit from it, too. I’d appreciate any of your comments :)

The full report from which the following summary is created can be found at: http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

Observation of climate change

  • Definition (climate change): all changes of climate state observed over longer time periods (decades or longer)
  • Warming of global temperatures: widespread, greatest at higher latitudes, warming over land greater than warming over oceans, ocean has been taking up over 80% of the
    heat being added to the climate system
  • Sea level rising: 1.8mm per year on average (1961-2003)
    (over 50 percent contribution due to thermal expansion)
  • Decrease in snow/ice extent in both hemispheres (annual average Arctic sea ice extent has shrunk by 2.7% per decade)
  • Trends in precipitation observed between 1900 and 2005:
    • increase: eastern parts of North and South America, northern Europe, central Asia
    • decrease: Sahel, Mediterranean region, southern Africa and southern Asia
  • Extreme weather events:
    • high chance for less cold days and nights, while the chance for warmer days and nights and heat waves over land will increase.
    • Likely increasing tropical storm occurrence in North Atlantic region since 1970

Observed Effects of climate change

  • High confidence that permafrost regions influenced
  • Very high confidence for earlier spring events
  • Shifts in ranges and changes in algal, plankton and fish abundance in high-latitude oceans.
  • More effects likely but not easy to distinguish the climate influence from other influence sources.


  • Antarctic sea ice shows no clear longterm trend, only inter-annual variations.
  • No clear trends for small-scale features.


to be continued… (soon)

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