The study of ice cores is adding to a growing body of evidence that Earth has heated up over the past century. The analysis of cores, taken from an ice field on the flank of a 26,293-foot mountain peak in Tibet, found that temperatures have risen for 50 years and that the past decade was the warmest. The cores also recorded changes in the monsoon cycles over 800 years that resulted in catastrophic droughts in southern Asia.
Ice cores hold a climate record that is as old as the ice field from which they are taken.
Ice fields studied in the mountainous regions of Tibet range in age from 40,000 years to 400,000 years. The cores can reveal periods of heavy snowfall or drought, annual temperatures, and many other components of climate, says Lonnie Thompson of Ohio State University, who led the latest research. Of particular concern from this study and two previous studies by the same team is the shrinking of snow caps or ice fields on some of the world's tallest mountains along the middle latitudes. For at least the past 10,000 years, these permanent ice fields have been an essential source of water for most of the world's population. As most schoolchildren learn, snow and ice accumulate in the winter atop mountains, then melt in the spring and summer to provide water for rivers.