Credit: ISTOCKPHOTO / LOOPS7

Natural processes, including solar activity and explosive volcanism, are known to have cooled the climate in the past. Mimicking these processes could counteract global warming, but a study suggests that the effects would not be uniform, with extra cooling needed in the tropics to balance high-latitude warmth.

Caspar Ammann and colleagues from the National Centre for Atmospheric Research in Boulder, Colorado, investigated the potential of climate engineering approaches that mimic natural processes to counter greenhouse-gas-driven warming1. Their modelling experiments revealed that injecting sulphate aerosols into the atmosphere and reducing solar insolation using mirrors would have to be much larger in effect than natural forcing to appreciably offset global warming.

In addition to the direct effect that greenhouse gases have on the climate, strong negative feedbacks in sea-ice extent, ocean heat content and winter westerly winds enhance warming, particularly at high latitudes, found the study. Consequently, if climate engineering was used as the sole solution to counter a complicated picture of warming, it would be necessary to induce greater cooling over the tropics to balance out polar warming.