Visualizing Greenland's Melting Ice

According to a new study, the Greenland ice sheet lost a record-breaking (and intuition-defying) 532 billion tonnes worth of ice in 2019. The Greenland ice sheet refers to the ice covering Greenland, which makes up the second largest body of ice in the world after the Antarctic ice sheet.

As I mentioned in the previous newsletter, Greenland’s melting ice is a Big Deal because it’s the single largest contributor to rising sea level. 2019’s melt alone is sufficient to raise global sea levels by 1.5 millimeters, enough water to hypothetically cover the state of California to a depth of 4 feet.

As climate scientist Andy Shephard told BBC News, “If Greenland's ice losses continue on their current trajectory, an extra 25 million people could be flooded each year by the end of this century.”(If all the ice in the Greenland ice sheet were to melt, it would raise global sea levels by about 7 meters, or 24 feet, although this would take centuries to occur.)

The ice is lost mainly through melting on the surface, as well as through ice at the edge of the sheet either falling into the ocean or melting underwater. Since the early 2000s, NASA satellites have made detailed measurements of Earth’s gravitational field, which allows scientists to effectively weigh different parts of the Earth.

The graph above shows last year in the context of the past two decades of ice loss. The vertical axis shows Greenland’s lost mass in billions of tonnes. Each year there’s a large drop in summer, followed by a small recovery in winter as snowfall accumulates.

Because the summer ice loss exceeds the ice gained from winter snowfall, we end up with this staircase-like graph. The drop in 2019 was larger than any preceding it, and the rate of melting is accelerating.

Lately the steps in this staircase have been getting larger, as Arctic temperatures have risen by nearly twice as much as global temperatures have in the past century. And climate models project that Arctic temperatures will rise two and a half times faster than temperatures at the tropics, so we can expect this trend to continue at least as long as our carbon emissions do.

Making Sense of Giant Numbers: A Guide for the Perplexed

But what does 532 billion tonnes of ice even mean? We might never