May 29, 2014, 4:58 pm

The science of melting ice


Thwaites Glacier in Western Antarctica. (AFP Photo/NASA Handout)

Re: “When Antarctica’s ice melts,” May 26 letter to the editor.

A reader wrote objecting to an article’s claim that melting sea ice will not increase sea levels. She explained that the above-water-line volume of a floating object will, when the object is submerged, raise the water’s level. While this is generally true, melting ice is different. Since this issue is relevant to the vital issue of global warming, it should be clarified.

If a floating object is submerged, it will raise the level of the water by the volume of the object above the water line. But this is true of ice only if it remains frozen. Water has the peculiar property of expanding when it freezes. Thus, a given amount of water will occupy more space when frozen than when liquid, but its weight is unchanged. Floating objects displace an amount of water equal to their weight. A given amount of water, when frozen, will weigh just as much as it would were it still liquid — and would displace the same amount of water. Thus, melting sea ice will have no effect on sea levels.

This does not mean predictions of rising sea level can be dismissed. To my mind they are as accurate as they are alarming. When the huge amounts of ice now on land in Antarctica and Greenland melt, the water will run into the oceans and will raise sea levels, catastrophically for places like the Maldive Islands, southern Florida and, quite likely, New York City.

D.R. Miklich, Denver

This letter was published in the May 30 edition.


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