Cold shock
After three months crunching out temperature and weather maps for the planets with a resolution of 200 square kilometres, the worlds emerged from a 40-year lifespan. The doubled-CO2 world turned out just as you'd expect from other climate models. It warmed more in winter than summer at high latitudes, because there was less sea ice to reflect the sunlight and keep the polar regions cool. Overall, the global temperature went up by 1.75°C, the volume of sea ice went down, and it rained more at high latitudes as additional water evaporated into the clouds near the equator.

But when it came to the geoengineered planet, the researchers got a shock. This world looked very much like the control model. Only about 15 per cent of the planet's surface was significantly warmer or colder than the control, compared to a whopping 97 per cent for the doubled-CO2 model. As the results began to appear, Caldeira raised an eyebrow at the numbers. And the more he saw, the less he understood. "Oh my God, even in the winter it's all cancelling out. What's going on?" he remembers asking Govindasamy.

After some thought, they realised that sea ice was playing a crucial role in the geoengineered world. Cooling the planet meant that more sea ice formed, and not only did the white ice reflect more light, it also insulated the warmer ocean water from the overlying air. That kept the winter atmosphere near the poles nice and nippy. And somehow that was enough to cancel out global differences between the warming from CO2 and the cooling from the reduced sunlight.

Can the results be trusted? "I believe about 85 per cent that the local seasonal effect will be cancelled," says Govindasamy. Mike MacCracken, executive director of the National Assessment Coordination Office in Washington DC and author of several papers investigating g
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-207-331-2751
New Scientist
19-Sep-2000