Why is Greenland covered in ice?

There have been many reports in the media about the effects of global warming on the Greenland ice-sheet, but there is still great uncertainty as to why there is an ice-sheet there at all.

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<p><a href="http://www.physorg.com/news139060720.html">Why is Greenland covered in ice?</a></p> <p>There have been many reports in the media about the effects of global warming on the Greenland ice-sheet, but there is still great uncertainty as to why there is an ice-sheet there at all.</p>