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INSTALLING huge mirrors in space would help reverse global warming, but they would come at a price: less rain for the Americas and northern Eurasia.

Previous studies have shown that geoengineering cannot restore both temperature and rain to previous levels, but they could not specify what a geoengineered climate would look like.

, Germany, and his colleagues played out the same simple scenario in four different climate models. In each one, he quadrupled carbon dioxide levels from pre-industrial levels. Then, to mimic the effect of space-borne mirrors, he reduced the amount of incoming sunlight to precisely compensate for the extra trapped heat.

Reducing incoming sunlight brought the average global temperature back down to its pre-industrial 13.6 °C, but the poles warmed and the tropics cooled. Global rainfall dropped, with parts of North and South America and northern Eurasia receiving 10 to 20 per cent less (). This means that space mirrors might not save the US from the severe droughts predicted for later this century.