Act globally

Three years ago, Nobel laureate Paul Crutzen rocked the boat of the climate discussion by suggesting it might become necessary to inject one million tons of sulphur into the stratosphere every year and let it burn there to form sulphate aerosols. Inspired by the cooling effect of the Pinatubo eruption in 1991, he proposed that such drastic measures might be the only way to avert catastrophic climate change. Nevertheless, such drastic geoengineering projects have retained an aura of science fiction and impracticability so far. A detailed report, Geoengineering the climate, published by the Royal Society in September, has now moved this topic a step closer to scientific respectability. The report was prepared by a group of 12 scientists chaired by Earth scientist John Shepherd from the University of Southampton. In response to the burning question of what we should do about climate change, the report makes a clear statement of priority. The best option, and thus the most urgent project to promote, is to stop the rise in atmospheric CO2 levels by drastically reducing man-made emissions. Thus, it remains true that the upcoming climate meeting at Copenhagen is the crucial event determining the fate of our planet for the rest of the 21st century (Curr. Biol. 19, R537). Only as a plan B, the experts recommend to investigate the feasibility of geoengineering methods like the one proposed by Crutzen. They make a crucial distinction between two kinds of possible projects, namely those that remove CO2 from the atmosphere, and those that reduce the solar energy retained by our planet. Between these two groups of measures, the report expresses a clear preference for reducing CO2 over managing solar radiation. It argues that the latter strategy would establish a non-natural and difficult to predict new equilibrium between an atmosphere with elevated CO2 content and a reduced solar energy Michael Gross looks at a report on how carbon emissions could be tackled. Act globally uptake, which will stop the runaway global warming but may fail to address many of the side effects of CO2 emission, including the changes in tropical storm and precipitation patterns, and the acidification of the oceans, which already presents a massive threat to corals and the oceanic biosphere in general (Curr. Biol. 18, R1112). Thus, removing CO2 should be our plan B, while managing sunlight, Crutzen style, becomes relegated to plan C status. The authors of the report note, however, that global cooling methods using sun blocks do have the advantage of acting much more quickly than CO2 reduction or removal. Hence, they suggest that these strategies should also be assessed as the ultimate emergency measure to be deployed if and when the climate approaches a tipping point and the preferred options have failed to deflect the threat. Among the various solar radiation management options considered as a last resort, ranging from painting roofs white to sending mirrors into orbit, the report expresses a preference for Crutzen’s stratospheric aerosols while also emphasizing the