Volcanic eruptions play a large part.

• Position: Climate

Volcanic eruptions over the last 1,000 years have exerted a heavy influence on global climate, according to a study led by researchers at the University at Albany (N.Y.). The impact is felt most dramatically near the equator, where eruptions have led to reduced rainfall in both the summer monsoon and winter seasons, as well as a cooling trends across entire continents.

Writing in Earth System Dynamics, UA researchers Christopher Colose and Mathias Vuille, along with Allegra LeGrande of the NASA Goddard Institute for Space Studies, New York, document the influence of large, explosive (Plinian) volcanic eruptions during the last millennium. They found that the narrow precipitation belt in the deep tropics--the intertropical convergence zone (ITCZ)--would shift following massive eruptions.

ITCZ is a critical resource, producing some of the most-intense rainfall on the planet, providing water for ecosystems and agriculture, and affecting hundreds of millions of people. The monsoons, linked to ITCZ, equally provide vital rainwater used for sanitation, drinking, hydropower production, and irrigation in tropical countries all over the world, from India to Bolivia.

"We looked at how volcanic eruptions in one hemisphere impact the tropical rain belt and found that it tends to move toward the opposite hemisphere," says Colose, a graduate researcher who is completing his Ph.D. in atmospheric and environmental sciences.

It long has been known that volcanic eruptions cool the planet and reduce rainfall averaged across the entire globe. "However, following Plinian eruptions, the rain belt moves away from the hemisphere where the volcano is located. So, if you're sitting somewhere south of the equator in South America, and an eruption goes off in...