Ocean Warmth Tied to African Drought

The authors of the study say that the heating of [the Indian Ocean], which lacks the natural variability of the Pacific and Atlantic, is one of the clearest fingerprints pointing to human-caused climate change. The study compared the observed 20th-century changes in the oceans and weather patterns with 60 simulations of climate run on five computer models developed by different research centers.

The warming ocean changes the circulation of the atmosphere, causing more air to rise over the water, generating marine storms and rains, while at the same time causing the opposite motion in air masses over the adjacent continent, leading to less rain. By midcentury, he said, there could be a 10 to 20 percent drying in the February-to-April wet season compared with the average for the last half of the 20th century.

For the Sahel, beset by drought and famine for generations, the picture is less clear. The new study projects rainier times there as the boundary between warm and cooler portions of the Atlantic Ocean shifts. But other experts on African climate still see evidence that the Sahelian drought pattern could worsen. Dr. Kerry H. Cook, an atmospheric scientist at Cornell, said the frequency of extremely dry years matters more to vulnerable populations than longer-term shifts in average rainfall. She said such extreme dry seasons were directly related to warm temperatures in the Gulf of Guinea, the Atlantic waters beneath the westward bulge of central Africa.

Most climate experts agree that this gulf will warm as global temperatures rise, Dr. Cook said. If emissions of greenhouse gases are not curbed, she added, new computer simulations show that there could be twice as many “really harmful dry years” in the latter half of this century as there were in the late 20th century. Other experts on African climate said that uncertainties in projections were likely to remain high as long as big gaps persist in collecting basic meteorological data.

He was the lead author of a British report last year on African climate variability and trends that concluded, “The African climate-observing system is in a worse state than that on any continent and is deteriorating.”

Full article at the New York Times.