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New climate perspective adds feedback

24 May 2006

A team of European scientists have found that climate change estimates for the next century may have substantially underestimated the potential magnitude of global warming.

The scientists say that the actual warming due to human fossil fuel emissions may be 15% to 78% higher than warming estimates that do not take into account the feedback mechanism involving carbon dioxide and Earth's temperature.

Marten Scheffer from Wageningen University in the Netherlands and colleagues from the Potsdam Institute in Germany and the Centre for Ecology & Hydrology in Britain have reached their view by looking at ancient climate data in a new way. The scientists have not only been studying the effect of temperature on greenhouse gasses but also the reverse effect of greenhouse gasses on temperature.

The ancient climate data studied is from a period known as the Little Ice Age (1550-1850). Due to reduced solar activity this period was substantially colder than today and the atmospheric carbon level had dropped. This information has helped the scientists estimate how sensitive carbon dioxide concentration is to temperature and how much climate-carbon dioxide feedbacks will affect future global warming.

Marten Scheffer explains, "Although there are still significant uncertainties, our simple data-based approach is consistent with the latest climate-carbon cycle models, which suggest that global warming will be accelerated by the effects of climate change on the rate of carbon dioxide increase. In view of our findings, estimates of future warming that ignore these effects may have to be raised by about 50 percent."

The research is explained in a paper 'Positive feedback between global warming and atmospheric CO2 concentration inferred from past climate change' published in Geophysical Research Letters, 26 May 2006.

The news is covered on the BBC website.

Briefing note: 32/06