Abstract:
The status of climate change research
Lennart Bengtsson, Professor, Max Planck Institute, Hamburg
The latest IPCC report (2007) shows that climate research now virtually encompasses all aspects of the Earth’s climate system. This includes not only the atmosphere and the land surfaces, but also the oceans, the cryosphere and the way the Earth’s climate is affected by external processes such as volcanic eruptions and solar influences. The IPCC 2007 best estimate of the average surface temperature is projected to increase by 1.8-4.0°C at the end of the present century. This is not expected to occur through a monotonous change in temperature but will include considerable fluctuations that might affect the regional climate on annual to decadal time-scales in a noticeable way.
While there is a broad agreement that the recent global warming is caused by increasing accumulation of greenhouse gases there is a considerable uncertainty in the expected magnitude of the warming and the consequences this will have for the cryosphere, for sea level height and for the water cycle. Probably the major part of this uncertainty is due to model deficiencies including the treatment of clouds, hydrological processes and the carbon cycle. To reduce the uncertainty is fundamentally important, as an extreme warming would have severe societal consequences.
Here I wish to highlight three key areas, namely the mechanisms responsible for sea level rise including the role of recent gravity- and position measurements from space, expected changes in the Earth’s hydrological cycle and considerations of the predictability of the climate