But trying to resolve the problem through "geoengineering" could result in monsoonal rains in North America, East Asia, and other regions dropping by 5-7 percent compared to preindustrial conditions. Globally, average precipitation could decrease by about 4.5 percent.
"Geoengineering the planet doesn't cure the problem," says NCAR scientist Simone Tilmes, lead author of the new study. "Even if one of these techniques could keep global temperatures approximately balanced, precipitation would not return to preindustrial conditions."
As concerns have mounted about Climate-Change'>climate change, scientists have studied geoengineering approaches to reduce future warming. Some of these would capture carbon dioxide before it enters the atmosphere. Others would attempt to essentially shade the atmosphere by injecting sulfate particles into the stratosphere or launching mirrors into orbit with the goal of reducing global surface temperatures.
The new study focuses on the second set of approaches, those that would shade the planet. The authors warn, however, that Earth's climate would not return to its preindustrial state even if the warming itself were successfully mitigated.
"It's very much a pick-your-poison type of problem," says NCAR scientist John Fasullo, a co-author. "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."
The study appears in an online issue of the Journal of Geophysical Research: Atmospheres, published this week by the American Geophysical Union. An international team of scientists from NCAR and 14 other organizations wrote the study, which was funded in part by the National Science Foundation (NSF), NCAR's sponsor. The team used, among other tools, the NCAR-based Community Earth System Model, which is funded by NSF and the Department of Energy.
The research team turned to 12 of the world's leading climate models to simulate global precipitation patterns if the atmospheric level of carbon dioxide, a leading greenhouse gas, reached four times the level of the preindustrial era. They then simulated the effect of reduced incoming solar radiation on the global precipitation patterns.
"More research could show both the positive and negative consequences for society of such changes in the environment," she says. "What we do know is that our climate system is very complex, that human activity is making Earth warmer, and that any technological fix we might try to shade the planet could have unforeseen consequences."