Cave stalagmites give clues to how climate may respond to increases in atmospheric carbon dioxide since preindustrial times, U.S. scientists say. Researchers say stalagmites, building upward from cave floors, can reveal historical climate information about Earth\'s tropical regions, valuable since many existing historical climate records are based on polar ice cores and North Atlantic deep ocean sediments from high latitudes. \"Stalagmites are the ice cores of the tropics,\" California Institute of Technology geochemistry Professor Jess Adkins said. He and geochemist colleague Kim Cobb of the Georgia Institute of Technology have collected samples from stalagmites in caves in northern Borneo and measured levels of oxygen isotopes to reconstruct a history of the tropical West Pacific\'s climate over four glacial cycles from 210,000 to 570,000 years ago. Extreme drying in the tropics coincided with abrupt climate changes in the North Atlantic at the tail end of glacial periods, they said. However, the tropics didn\'t seem to show a response to all changes in higher latitudes, the researchers said, unless those changes were large and significant. \"It makes you wonder if maybe the climate system cares about what sort of hammer you hit it with,\" Adkins said. \"If you nudge the system consistently over long timescales, the tropics seem to be able to continue independently of the high latitudes. But if you suddenly whack the climate system with a big hammer, the impact spreads out and shows up in the tropics.\"