HOW much will Earth warm this century? The best answer to this killer question remains broad, but a study has narrowed the range of likely temperatures 鈥� and comes down on the warmer side.
As we pump more greenhouse gases into the atmosphere, temperatures rise. The consensus among climatologists is that if the amount of carbon dioxide doubles, temperatures will rise by about 3 掳C. But this figure, known as climate sensitivity, is an estimate and falls within a range of 2 to 4.5 掳C, as calculated by the Intergovernmental Panel on Climate Change (see 鈥�Climate change: It鈥檚 even worse than we thought鈥�).
and of the National Center for Atmospheric Research in Boulder, Colorado, have narrowed this range and suggest the lower limit is 2.5 掳C.
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Much of the uncertainty stems from clouds, whose effects climate models struggle to simulate. Fasullo and Trenberth bypassed this problem by using satellite records of relative humidity, which influences cloud formation, instead. Humidity is unevenly distributed, and changes over the year. The pair looked at climate models with various sensitivities to see how well they reproduced these real-life changes.
聯Much of the uncertainty stems from clouds, whose effects climate models struggle to simulate聰
Models with climate sensitivities at the lower end of the scale did badly, often reporting high humidity in regions where it was low. Those with sensitivities around 4 掳C did best (). 鈥淲e have found a new metric for evaluating climate models,鈥� says Trenberth. 鈥淭he models with a higher sensitivity are doing a better job.鈥�
鈥淚t鈥檚 a pretty impressive step,鈥� says of the Swiss Federal Institute of Technology in Zurich, though he cautions that just one study should not be taken as gospel. Trenberth suggests the sensitivity is about 4 掳C, but he says 3 掳C is still 鈥渧ery viable鈥�.
