Rapid melt fascinates and terrifies.

It used to be that Iceland was green and Greenland was icy. There's an old story that those switched names were an effort by Icelanders to fool the Vikings and send them to invade a desolate arctic wasteland instead of where they lived. But the switched names have held true for centuries, which means Greenland is supposed to be covered by ice.

But that's changing fast. The Greenland ice sheet is melting faster and in more ways than people thought it would: there are the surface pockmarks of meltholes pitting the ice surface. There are the moulins -- vertical fissures hundreds of meters deep. Melt water runs into them and, it's thought, gets under the ice sheet, allowing it to shift. And there are the massive calving events where vast blocks of ice break off the edge of the sheet and fall into the ocean.

Konrad Steffens is on the sheet, studying all of this and tracking its progress. And this week his work is being featured in a series of stories on NBC Nightly News as reported by environmental correspondent Anne Thompson. You can also find out about the practical realities and challenges of covering the story.