The news was bad this week for the Marshall Islands, South Florida, the Netherlands and Lower Manhattan.

Contrary to earlier predictions, satellite data from Greenland’s ice sheet shows that climate change is melting it a lot faster than we thought.  When all that land-based water melts into the sea, the ocean will rise and permanently flood low-lying land around the world, including the places I named above.

Why is it melting so fast?  A big reason is the action of numerous superglacial lakes (i.e. lakes on top of the glacier) that form in the summer. The lakes collect ice melt but they also speed up melting because they empty all at once — downward! — and flow under the ice sheet, lubricating it and sending it much faster to the sea.

If you find this hard to imagine — or even if you don’t — click on the screenshot above (or here) to see a video showing how this happens.

At another site, the scientists camped near a superglacial lake to study its development.  One day the lake disappeared but the weather was so foggy they couldn’t see what happened. All around them the ice they were standing on cracked and heaved and boomed.  Scary!

When the weather finally cleared they retrieved the measuring devices they’d left on the lake bottom (now dry) and pulled the data.

The lake they’d camped next to — two miles wide and 40 feet deep — had emptied into the ground 3,000 feet below in only 40 minutes!

Yow!

(screenshot from National Geographic online video.  Click on the image to watch the show)