Posted on 11 May 2015 by John Abraham

As I’ve previously noted, one of the most challenging problems in climate science deals with how to measure the Earth’s system. Whether ocean temperatures, atmospheric temperatures, sea level, ice extent or other characteristics, measurements have to be made with sufficient accuracy and geographical coverage so that we can calculate long-term trends. In some parts of the planet, the measurements are particularly daunting because of the ruggedness of the terrain and the hostility of the environment.

This brings us to a new study just published on Antarctic ice loss by Christopher Harig and Frederik Simons of Princeton. They work in the Princeton Polar Ice program. This study used satellite measurements to determine the rate of mass loss from this large ice sheet.

The ice sheet has two parts, a stable and large eastern part and a smaller and less stable western portion. The impact of climate change on these portions is different. The western part is losing mass at an increasing rate over the past years. In the east, however, the information is less clear. Increased precipitation (snowfall) is adding to the ice there, even while portions of the ice are warming.

The satellite method that these authors used actually measures the gravitational pull of the ice on two orbiting satellites. The huge ice sheet has such a large mass that it attracts objects toward it. As the ice melts and flows into the oceans, the attraction decreases – it is this change that is measured. The satellites are part of the Gravity Recovery and Climate Experiment (GRACE) project.

In the past, the satellites could only be used to make gross measurements over large areas. Their ability to separate what is happening in different regions is very limited. For such local measurements, other techniques had to be used.

The new paper provides an improvement to the resolution of GRACE. They find that the western part of Antarctica is losing mass at 121 billion tons (gigatons) a year. This rate has increased recently. In particular, in one region (the Amundsen Sea coast, the ice loss has doubled in the past six years). In the east, there is a small mass gain (approximately 30 gigatons a year). This mass gain partially offsets what is happening in the west but there is still a large loss of water to the sea each year.

I asked the lead author about this study and he told me,

It is very important that we continue long term monitoring of how mass changes in ice sheets. For West Antarctica in particular this is important because of how it is thought to be more unstable, where the feedbacks can cause more and more ice loss from the land over time. These strong regional accelerations that we see are very robustly measured and imply that Antarctica may become a major contributor to sea level rise in the near future. This increase in the mass loss rate, in ten years, accelerations like that show that things are beginning to change on human time scales.