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HOME > PAST ISSUE > July-August 1999 > Article Detail

FEATURE ARTICLE

Rapid Climate Change

New evidence shows that earth's climate can change dramatically in only a decade. Could greenhouse gases flip that switch?

Kendrick Taylor

Ice, the Museum of Climate

One can learn a lot about what controls climate by studying glacial ice. When snow falls, it collects insoluble dust particles, soluble compounds and the water in the snow itself. In some places more snow falls in a year than melts or sublimates away. Annual layers of snow pile up, with atmospheric gases filling the open pores between snow crystals. The weight of accumulating snow compresses the pores in the snow below, turning the snow into ice and trapping the atmospheric gases. The dust, chemicals and gases in the ice reflect the environment along the water's journey from distant sources to the glacier. They record how cold it was, how much snow fell in a year, what the concentration of atmospheric gases was and what the atmospheric circulation patterns were.

We can identify annual layers in the ice because the concentration of sea salts, nitrate and mineral dust and the gas content in winter snow are different than in summer snow. We count the annual layers to determine the age of the ice, and by measuring the thickness of the annual layers we can determine how much snow fell each year. The gas trapped between ice crystals offers a sample of the ancient atmosphere, and we can use it to determine what the concentrations of greenhouse gases such as carbon dioxide and methane were long before human beings measured the atmosphere directly. General patterns of atmospheric circulation can be reconstructed by using tracers such as soluble chemicals (for example, nitrate, ammonium, sodium and calcium) and rare earth elements in insoluble dust particles to determine how wind moved air and dust from the source regions for these compounds to the drilling site.








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