These bodies of ice are composed of two sections: the vast ice sheets that cover the interior of Greenland and Antarctica, and the peripheral glaciers at the ice sheets' edges. These peripheral glaciers, like glaciers elsewhere in the world, carry ice downslope to lower elevations.

In these cases, they release icebergs into the ocean. The meltwater from these icebergs is a large and growing source of sea level rise.

Both the ice sheets and the glaciers must be carefully studied to carry out what Joerg Schaefer, a glaciologist at Columbia's Lamont-Doherty Earth Observatory, calls "a key goal of cryospheric science around the world: understanding estimates of near-future polar ice melt, and thus of sea level rise."

The scientists who study the ice sheets and those who focus on peripheral glaciers often work independently, but the regions they study sometimes overlap. In other cases, some glaciers are excluded from both groups. This means estimates of sea level rise from Greenland and Antarctica may have some small amount of double-counting or missing mass loss.

As Schaefer told GlacierHub, "The Intergovernmental Panel on Climate Change reports do their best to coordinate the ice sheet and glacier estimates, but errors remain large."