ENSO and Drought
Can droughts in southern Africa have anything to do with ocean temperatures off the coast of Ecuador, more than 9,300 kilometers (about 5,800 miles) distant? They can, and they do. Scientists have a name for these long-distance linkages: they call them atmospheric teleconnections, after tele, the Greek word for "far away."
The most important periodic fluctuation in Earth's climate, after the seasons, is El Ni--o /Southern Oscillation, or ENSO--which affects weather and climate around the globe. ENSO is a change in the coupled ocean-atmosphere circulation patterns across the equatorial Pacific. In an El Ni--o year, dramatic warming occurs in the ocean off the coasts of Peru and Ecuador. One local effect is heavy rain in the normally arid coastal regions of those countries. But ENSO's climatic effects are global, including droughts in Australia, Indonesia and southern Africa, stormy weather in part of North America and a weakening of the Indian monsoon.
During most years, the waters of the eastern equatorial Pacific are cold (top). In El Nino years (bottom), the winds that usually push the cold equatorial surface waters westward reverse. This brings the warm waters of the western Pacific to the east.
The impacts of ENSO are felt worldwide, in part because the position of the jet stream changes, which influences storm tracks. The risk of drought in southern Africa--including Botswana (above)--increases by 120 percent in an El Ni--o year. Scientists are uncertain about how climate change will affect ENSO, but the stakes are high.