Geoengineering the Climate Could Reduce Much Needed Rain, Study Suggests

A proposed method to reduce future global warming could alter precipitation patterns throughout the world, according to a study led by scientists from the National Center for Atmospheric Research.

Known as geoengineering, the approach could cause a 4.5 percent decrease in the global average precipitation, the study found.

"It's very much a pick-your-poison type of problem," co-author John Fasullo said in a statement. "If you don't like warming, you can reduce the amount of sunlight reaching the surface and cool the climate. But if you do that, large reductions in rainfall are unavoidable. There's no win-win option here." 

Some geoengineering techniques would capture CO2 before it reaches the atmosphere. Other proposals include launching mirrors into orbit or shading the atmosphere by injecting sulfate particles in order to reduce global surface temperatures.

In this study, the researchers examined approaches designed to shade the planet, noting that the climate would not return to the way it was prior to the Industrial Revolution even if warming were mitigated.

The scientists looked at 12 leading climate models in order to simulate global precipitation patterns if atmospheric CO2 levels were to quadruple. This was followed by a simulation examining the effect of reduced incoming solar radiation on the global precipitation patterns.

As with other studies, the results showed that an increase in CO2 would lead to increased global average precipitation due to higher rates of evaporation.

Expanding on these results, the scientists examined what would happen in the case that incoming solar radiation was partially reflected high in the atmosphere.

The results showed a significant drop in precipitation amounts and frequency, though with variation depending on the area. For example, monsoonal rains would drop by 7 percent in North America, 6 percent in East Asia and South America, 5 percent in South Africa, and 2 percent in India.

"Geoengineering the planet doesn't cure the problem," lead author Simone Tilmes said. "Even if one of these techniques could keep global temperatures approximately balanced, precipitation would not return to preindustrial conditions."