(CNN) - Satellite images show Greenland's ice sheet dramatically changed in a matter of days earlier this month. Take a look.
On the left, you can see an image from July 8-th.
On the right is one taken on the 12-th.
You'll notice, there's a blob of white on the left-side image.
Look over to the right, and you can see that white has almost disappeared.
NASA says in the first image, nearly 40 percent of the ice sheet had thawed at or near the surface.
Then, the melting dramatically accelerated.
And by the 12-th, NASA estimates 97 percent of the sheet had thawed.
NASA says it's never seen anything like this in Greenland in more than 30 years of observations.
Scientists blame the "unprecedented" change on an unusually strong ridge of warm air.
Usually, Greenland sees about half of its ice sheet melt in the summer.