Photographer Timo Lieber’s new photo series, “Thaw,” captures one of the most startling and visible ways we can witness the melting of Greenland’s ice sheet. In July 2016, he photographed from above the melt lakes, which accumulate on top.

A host of factors make it difficult to estimate exactly how fast Greenland is melting (a question for which NASA hopes to have an answer in a few years). But what is clear is that the overall melt of the ice sheet is a major contributor to the rising of the ocean.