AGU conference on climate and civilizations

AGU Chapman Conference on Climates, Past Landscapes, and Civilizations, Santa Fe, N.M., March 22, 2011 The drying of Africa SANTA FE — About 2 million years ago seesawing ocean temperatures caused eastern Africa to dry out, new research suggests, setting the stage for early human evolution. Before that time, the world’s tropical oceans were pretty much the same temperature from east to west across their basins. But then for unknown reasons strong gradients developed; the western Pacific warmed up, for instance, while the east cooled. That shift changed tropical weather patterns and dried out eastern Africa. Peter deMenocal of the Lamont-Doherty Earth Observatory in Palisades, N.Y., reported the finding, which may resolve a longstanding mystery, on March 22. — Alexandra Witze Dry everywhere SANTA FE — Even as drought hammered Cambodia’s fading Khmer empire in the 14th century, North America was enduring its own dry spell. Normally when Southeast Asia is dry, southwestern North America is wet, says Kevin Anchukaitis of the Lamont-Doherty Earth Observatory in Palisades, N.Y. But new tree-ring studies suggest a peculiar break in that pattern, he reported March 22. An unusual form of the El Ni±o climate pattern apparently caused both continents to dry at once. The work helps illuminate the many factors that contribute to natural climate variability. — Alexandra Witze Tree islands out of trash SANTA FE — South Florida’s river of grass retains some of its biological diversity thanks to prehistoric rubbish piles. Hundreds of “tree islands” dot the Everglades, rising above the marsh to provide a home for trees and animals. In new research, four islands studied all rested atop mounds of bones, shells and other debris left by Native Americans 5,000 years ago, said Gail Chmura, a paleoecologist at McGill University in Montreal, on March 22. Earlier work had suggested the islands arose from a naturally occurring base. — Alexandra Witze Vikings off the hook SANTA FE — Don’t blame the Vikings — too much — for the failure of their settlements in Greenland. New studies of sediment cores from Lake Igaliku, next to one of the two main Norse settlements in Greenland, reveal that the settlers didn’t degrade their environment as much as some scientists have thought. Algae and other indicators in the cores show that free-roaming Norse sheep had only a subtle impact on the landscape, Bianca Perren of the University Franche-Comté in Besançon, France, reported March 22. In contrast, modern farming over the past few decades in the same region has caused unprecedented amounts of pollution and erosion. — Alexandra Witze