Using the ice age to predict global warming
Doubling the concentration of carbon dioxide (CO2) in the atmosphere would cause a global temperature increase of 3°C, according to a team of scientists from the Potsdam Institute for Climate Impact Research (PIK) in Germany. Their research is published in the journal Climate Dynamics. To determine how much global warming will result from increased concentrations of CO2 in the atmosphere, the researchers went back in time to the last ice age. Ice ages are caused by changes in the Earth's orbit, but a number of factors, including lower CO2 concentrations, contribute to make ice ages so cold. To disentangle the various factors influencing temperature, the scientists ran 1,000 climate computer models with variations in cloud behaviour, ocean currents and other factors affecting the climate. For each model, a scenario with a doubled CO2 concentration was computed. As expected, the 'climate sensitivity' (the amount of global warming resulting from a doubled CO2 concentration) varied greatly between models. The researchers then ran the models with data from the last ice age, to see which would correctly predict the climate. Models whose sensitivity to CO2 is too high would predict an ice age that is too cold, and vice-versa. The scientists found that doubling the concentration of CO2 could lead to global warming of between 1.2 and 4.3°C with the most likely value being around 3°C. This is in line with the results of other studies which used different methods. The EU hopes to limit global temperature rise to not more than 2°C above pre-industrial levels to prevent the worst predictions of the impacts of climate change from becoming a reality.
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