We can’t reverse global warming by triggering another catastrophe

by George Monbiot

Nobel Prize laureate Paul Crutzen suggests we use either giant guns or balloons to inject sulphur into the stratosphere, 10km or more above the surface of the earth. Sulphur dioxide at that height turns into tiny particles – or aerosols – of sulphate. These reflect sunlight back into space, counteracting the warming caused by manmade climate change.

In 2002 the Journal of Climate published an astonishing proposition: that the great droughts which had devastated the Sahel region of Africa had been caused in part by sulphate pollution in Europe and North America. Our smoke, the paper suggested, was partly responsible for the famines that killed hundreds of thousands of people in the 1970s and 1980s.
By reducing the size of the droplets in clouds, thereby making them more reflective, the sulphate particles lowered the temperature of the sea’s surface in the northern hemisphere. The result was to shift the intertropical convergence zone southwards. This zone is an area close to the equator in which moist air rises and condenses into rain. The Sahel, which covers countries such as Ethiopia, Sudan, Chad, Niger, Burkina Faso and Senegal, is at the northern limits of the zone. As the rain belt was pushed south, those countries dried up. As a result of the clean air acts, between 1970 and 1996 sulphur emissions in the US fell by 39%. This appears to have helped the North Atlantic to warm, allowing the rains to return to the Sahel in the 1990s.

Since then, several studies – published in the Proceedings of the National Academy of Sciences, Geophysical Research Letters and the Journal of Geophysical Research – have confirmed these findings. They show that the 40% reduction in rainfall in the Sahel, which has “few if any parallels in the 20th-century record anywhere on Earth”, is explicable only when natural variations are assisted by sulphate aerosols. We killed those people.

Guardian