National Geographic : 2004 Sep
Cutting to the I Core Stalagmites provide a trove of past climate data for University of Iowa geologist Jeff Dorale (top), holding a sample from Crevice Cave in southeastern Missouri. By measur ing isotopes of uranium, as well as mud embedded in the slow-growing stalagmites, Dorale and colleagues believe they can link El Nino events to flooding in the cave and higher rainfall over the past 10,000 years. Pack Rats have been hoarding seeds, leaves, and twigs in the arid Southwest for more than 30,000 years. Preserved in crystallized urine, such middens give geologist Camille Holmgren (middle) a snapshot of an evolving landscape in Arizona's Pelon cillo Mountains. During the last ice age the area was cooler, wetter, and covered with pinon pines and junipers. Corals produce annual rings like trees. The density of a ring depends on sea surface temperature, which, according to Woods Hole researcher Anne Cohen (bottom), has risen dramatically off Bermuda in 50 years. "Those temperatures were pretty steady from 1850 to 1950," says Cohen. "Then boom! They just shot up. You can see global warming right there." Tree Rings like those in a hemlock log buried for a millennium and uncovered by Alaska's retreating Columbia Glacier, give geologist Greg Wiles (right) an annual regional tem perature record from A.D. 585 to the present. "Living trees seem to be expe Sriencing stresses they haven't seen in the past thousand years," Wiles says.