How do scientists measure the rate at which glaciers are melting?

Good question! For glaciers located in easily accessible places, scientists can monitor the glaciers directly. For example, it is relatively easy to measure how much ice has melted at a glacier like that shown in Figure 7.2.1-10 But most of the world’s glacial ice is in Greenland and Antarctica, where such direct observations are not currently possible. To measure this melting, since 2002, scientists have used an amazing set of measurements from NASA’s GRACE mission.

GRACE uses two satellites that together can measure very small changes in the strength of gravity as they pass over different parts of the Earth. They are so sensitive that they can tell whether ice has melted in Greenland and Antarctica because loss of ice means reduced mass and therefore also a very slightly reduced strength of gravity in these regions. In fact, the GRACE satellite measurements can also be used to measure many other small changes in the distribution of mass on Earth, including changes that occur when flooding weighs down land after a storm.

Figure 1 below shows GRACE data for ice melting in Greenland and Antarctica. Notice that ice loss is clearly happening in both places, but the rate of loss has been faster in Greenland.