This map shows the retreat of Mount Kilimanjaro's ice cap since 1912. During the period shown, more than 80 percent of the mountain's glaciers were lost. Researchers are working against time to collect ice cores from Kilimanjaro's rapidly shrinking ice fields so that they may collect and analyze clues to past climate conditions at this tropical locale. Scientists predict that all the ice on the mountaintop will probably be lost within 15 years. [One of 5 related images. See Next Image.]
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Ice cores contain an abundance of information about the Earth's climate in the past. They are the most effective natural recorder of climate change, more so than tree rings or sediment layers. Ice cores taken from certain undisturbed locations can contain an uninterrupted, detailed climate record, extending back hundreds of thousands of years, that can include temperature, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity and a variety of other climate indicators.
In 2000, National Science Foundation-grantee Lonnie Thompson, a geological science professor at Ohio State University (OSU), led an expedition to drill six ice cores from the ice fields on Mount Kilimanjaro. While camping for a month at their drill site, located above 19,300 feet, Thompson and his team collected 215 meters (705 feet) of frozen ice core, which they brought back to OSU's Byrd Polar Research Center.
Analysis of the core suggests dramatic changes in the climate and temperature on and around Kilimanjaro since the ice fields were formed approximately 11,700 years ago. For example, around 9,500 years ago the landscape was far wetter and different. Today, Lake Chad is the fourth largest body of water on the African continent, measuring about 17,000 square kilometers. But 9,500 years ago it covered some 350,000 square kilometers--an area larger than the Caspian Sea!
Analysis of the ice cores also indicates evidence of three catastrophic droughts that took place:
- A 500-year-period beginning around 8,300 years ago, when methane levels in the ice dropped dramatically. Thompson believes this represents a time when Africa's lakes were drying up.
- An abrupt depletion in oxygen-18 isotopes that researchers believe signals a second drought event occurring around 5,200 years ago.
Thompson believes that whatever happened to cause these dramatic climate changes in the past could certainly occur again. He has already predicted that Kilimanjaro's ice fields will vanish within 15 years. His team found that the summit of the ice fields has lowered by at least 17 meters (nearly 56 feet) since 1962, an average shrinkage of about a half-meter in height each year. In addition, the margin of the ice field has retreated as much as 1 meter since 2000--a meter's worth of ice lost from a wall 50 meters (164 feet) high. (Year of image: 2000)
- A visible dust layer in the ice cores dating back to about 4,000 years ago. Thompson believes this marks a severe 300 year drought that struck the region. Historical records show that a massive drought rocked the Egyptian empire at that time. According to Thompson, up until this period, people had been able to survive in areas that are now just barren Sahara Desert.