Why we need to keep an eye on the ice sheets


Loss of Arctic ice isn't just a threat to polar bears. Climate scientist James Hanson has just published a science brief on the NASA website about why those ice sheets are so important (besides providing an habitat for polar bears) and why we need to keep funding research that uses satellites to monitor the state of the world's ice sheets.

It is easy to see why this feedback amplifies the climate change, because reduction of ice sheet size due to warming exposes a darker surface, which absorbs more sunlight, thus causing more warming. However, it is difficult for us to say how long it will take ice sheets to respond to human-made climate forcing because there are no documented past changes of atmospheric CO2 nearly as rapid as the current human-made change.

One big uncertainty is how fast ice sheets can respond to warming. Our best assessment will probably be from precise measurements of changes of the mass of the Greenland and Antarctic ice sheets, which can be monitored via measurements of Earth's gravitational field by satellites.

Figure 2 shows that both Greenland and Antarctic ice sheets are now losing mass at significant rates, as much as a few hundred cubic kilometers per year. We suggest that mass loss from disintegrating ice sheets probably can be approximated better by exponential mass loss than by linear mass loss. If either ice sheet were to lose mass at a rate with doubling time of 10 years or less, multi-meter sea level rise would occur this century.

The available record (Fig. 2) is too brief to provide an indication of the shape of future ice mass loss, but the data will become extremely useful as the record lengthens. Continuation of these satellite measurements should have high priority.

Via Michael Noble