Reduced US Air Pollution Will Boost Rainfall in Africa's Sahel, Says Study

Falling sulfur dioxide emissions in the United States are expected to substantially increase rainfall in Africa's semi-arid Sahel, while bringing slightly more rain to much of the U.S., according to a new study in the Journal of Geophysical Research: Atmospheres.

Pollution filters placed on coal-fired power plants in the United States starting in the 1970s have dramatically cut emissions of sulfur dioxide, a toxic gas that contributes to acid rain and premature deaths from respiratory and cardiovascular diseases.  If U.S. sulfur dioxide emissions are cut to zero by 2100, as some researchers have projected, rainfall over the Sahel could increase up to 10 percent from 2000 levels, computer simulations published in the study suggest.

"Reducing emissions in one region can influence rainfall far away because our global atmosphere is interconnected," said the study's lead author, Dan Westervelt, an atmospheric scientist at Columbia University's Lamont-Doherty Earth Observatory.  "We show that the health and environmental benefits of U.S. clean air policies extend to global climate as well."

Sulfur dioxide simultaneously cools and dries earth's climate by reflecting sunlight back to space and suppressing heat-driven evaporation near the ground.  Though prior research has linked high sulfur emissions in Europe and Asia to the Sahel's severe droughts of the 1970s and 1980s, this study is the first to look at how U.S. emissions influence precipitation in various regions globally.

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