Northern Hemisphere Snow and Ice Chart

One way of gathering information about climate change is to measure the areas of the earth covered by snow and ice, and then examine these measurements for long-term trends. But making accurate measurements of huge, irregular portions of the planet’s surface requires special methods. Satellite imagery is an ideal technique for difficult situations like this.

Satellites orbiting over the earth’s poles take numerous photographs of high-latitude areas; these photographs are then combined with maps of the area. Because snow and ice reflect light differently, areas covered by snow can be distinguished from ice-covered zones. These differences allow researchers to create precise maps of current snow and ice cover. Such maps can then be compared with maps made at other times to determine whether the extent of snow and ice cover in particular areas has been changing over the long term. Variations in snow and ice cover could reflect a number of effects of a shift in climate, including changes in both air temperatures and precipitation patterns.

Evidence indicates that polar regions are already showing the effects of climate change. Since the 1950s, Alaska has warmed by an average of 4 degrees Fahrenheit. Satellite data indicates the extent of Arctic sea ice has shown a net decrease of 2.9% per decade since 1978.