A palaeobiologist calls for greater biological realism in climate models.

The world's most sophisticated climate models fail to adequately replicate climate at high latitudes and over continents' interiors during ancient periods of greenhouse-gas-induced warming: the wintertime predictions are consistently too cold. This makes me worry that the field is missing fundamental feedback processes that amplify warming. If so, climate models might be underestimating how much anthropogenic warming will happen in the future.

What might these mysterious processes be? Lee Kump and David Pollard of Pennsylvania State University in University Park think they have found one. They propose that marine phytoplankton that emit dimethylsulphide — already recognized as a major source of cloud-seeding particles far out to sea — became thermally stressed during the Cretaceous period (100 million years ago). As a result, the phytoplankton grew more slowly and reduced their emissions. Fewer biologically derived aerosol particles meant fewer nuclei for cloud condensation, which, in turn, led to less extensive cloud cover and more transparent clouds. Solar radiation was thus reflected less, and polar temperatures rose by 10–15 °C (L. R. Kump and D. Pollard, Science 320, 195; 2008).

Kump and Pollard's work is exciting for its dramatic result. Nevertheless, the duo's findings are ultimately unsatisfactory; the effects of heat on biological aerosol emissions need to be better described in their model for it to generate really solid conclusions. Although some recent field and laboratory experiments do suggest that marine algae produce less dimethylsulphide when carbon dioxide concentrations approach those of the Cretaceous, much more research is needed. If such results agree with Kump and Pollard's assumptions, I might worry less about climate models — but maybe even more about global warming.

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