Great lakes reach highest levels of freeze since 1994

NASA's Aqua satellite has shown the mostly frozen state of the Great Lakes on Feb. 19. On that date, ice spanned 80.3 percent of the lakes, according to NOAA's Great Lakes Environmental Research Laboratory in Ann Arbor, Michigan.

The ice reached an even greater extent on Feb. 13, when it covered about 88 percent of the Great Lakes - coverage not achieved since 1994, when ice spanned over 90 percent. In addition to this year, ice has covered more than 80 percent of the lakes in only five other years since 1973.

The average annual maximum ice extent in that time period is just over 50 percent. The smallest maximum ice cover occurred in 2002, when only 9.5 percent of the lakes froze over.

Scientists say it's understandable that the Great Lakes have had so much ice this year considering the cold temperatures in the region that persisted through the winter.

Cold air temperatures remove heat from the water until it reaches the freezing point, at which point ice begins to form on the surface, explained Nathan Kurtz, cryospheric scientist NASA's Goddard Space Flight Center in Greenbelt, Md.

Nathan Kurtz, cryospheric scientist NASA's Goddard Space Flight Center in Greenbelt, Maryland, said that persistently low temperatures across the Great Lakes region are responsible for the increased areal coverage of the ice, asserting that low temperatures are also the dominant mechanism for thickening the ice, while secondary factors like clouds, snow, and wind also play a role.