ASK TOM: Global warming raising lake levels?

Dear Tom,

We read about global warming raising sea levels. Does this hold true for Lake Michigan as well?

—David Schaffer


Dear David,

It does not, because Lake Michigan and all the Great Lakes, unlike the oceans, are not the final repository of the world’s water. The Great Lakes drain into the Atlantic Ocean via the St. Lawrence River, and their volume of outflow increases when the level of the lakes rises. It’s a different for story with the oceans. Water, once it finds its way into the world’s oceans, can’t drain out; it can escape the oceans only by evaporation. Researchers believe sea-level rise will be the result of melting land ice (mountain glaciers and the Greenland ice cap) and accelerated “drainage” of ice into the oceans from the icecaps of Greenland and Antarctica. Thermal expansion of warming ocean water will also add contribute to sea-level rise.