Faced with the immense threat of global warming, and the refusal of world leadership to act sufficiently, many people have wondered if it is possible to keep the planet habitable through deliberate cooling. Many versions of this idea, known as geoengineering, have been proposed, but a study of the most widely discussed idea has found a nasty side-effect.
Volcanoes inject a lot of sulfur dioxide high into the atmosphere, where it reflects sunlight. Really large eruptions produce a noticeable dip in global temperatures for a year or two thereafter. Human activity already releases cooling particles into the atmosphere, but the effect is swamped by carbon dioxide and methane emissions. However, we could deliberately raise our output of suitable particles, in an approach known as stratospheric aerosol injection (SAI), to bring average temperatures closer to balance.
Certain risks with SAI have already been identified, but a paper in Nature Communications outlines an additional one – more severe droughts in one of the most vulnerable parts of the planet. Dr Anthony Jones of the University of Exeter warns that the consequences could be devastating.
"Our results confirm that regional solar geoengineering is a highly risky strategy which could simultaneously benefit one region to the detriment of another," Jones said in a statement. "It is vital that policymakers take solar geoengineering seriously and act swiftly to install effective regulation."
Jones modeled the effect of SAI from the most industrialized parts of the planet. He found some positive effects, including a reduction in tropical cyclones, but at the price of less rainfall over Africa's Sahel.
The Sahel, immediately south of the Sahara, houses the poorest people on the planet. Consequently, residents have few reserves to fall back on, and the frequent droughts produce mass starvation, including one in the eastern Sahel right now. If such droughts become more intense or more frequent, it will be a human catastrophe almost unmatched in history. SAI in the southern hemisphere would have the opposite effect, but would be harder to achieve given the much lower population and industrialization there.