RECENT GREAT-LAKES ICE TRENDS

Analysis of ice observations made by cooperative observers from shoreline stations reveals significant changes in the ice season on the North American Great Lakes over the past 35 years. Although the dataset is highly inhomogeneous and year-to-year variability is also quite large, there is a statistically significant indication that the end of the ice season (as defined by the time at which ice departs from the observer stations in spring) has come increasingly early at a number of locations. The earlier ice departure is reflected in a somewhat earlier spring runoff through the St. Lawrence River over the same time period and correlates with increases in springtime temperatures at stations in the region. This example of a trend toward warmer, earlier springs in the upper Midwest is consistent with results from a number of other regional datasets. Because the ice observations began in the mid-1950s, other analyses, including comparisons with modern satellite datasets, could provide a useful tool for monitoring future climate change.