New satellite data finds the Greenland ice sheet lost mass in the noughties

Scientists are particularly interested in monitoring changes in the mass of the polar ice sheets because this provides a good measure of climate change over recent decades, and can help inform future estimates of sea level rise.

Measuring ice sheet mass has been made easier by the launch of satellites in 2002 that monitor changes in the Earth’s gravitational field. The gravity measurements taken by the satellites can then be used to reconstruct changes in the melting or accumulation of ice sheets.

Now, a new  study (published online in the Journal of Geophysical Research) has looked at what the satellite data tells us about changes in the Greenland ice sheet between 2002 and 2009 – the data that’s currently available.

They found that Greenland is losing ice overall, although there has been a slight accumulation of ice at the centre of Greenland. The ice loss is particularly severe at Greenland’s edges, with both northwest and southeast Greenland showed an overall decrease in ice mass. These findings agree with previous studies. However, this new research showed the rate of ice loss varied from area to area – it accelerated in the north-west of Greenland, but slowed down in the south-east after 2007, and varied from year to year.

These regional and temporal variations suggest that localised regional climate conditions have a significant impact on the ice sheet. It’s this kind of complexity that makes ‘big picture’ assessments of the health of large ice sheets difficult. Another recent  study of three Greenland glaciers, for example, showed vastly different rates of ice loss over the last decade.

This highlights the importance of considering long and continuous data series in order to determine long-term trends. As the satellite researchers point out, the observations from the satellites which span just 7 years show that:

“…it is very challenging to quantify Greenland’s long-term ice mass change rates, and some observed apparent accelerations might simply be a reflection of the interannual variability. Therefore, caution should be applied when using a short record of data to infer ‘long-term’ variability, such as the ice sheet mass change.”

However, combining records from other techniques with satellite measurements can provide useful information about long-term trends. For example, recent  research combining satellite data with another technique provided an 18-year record of ice mass balance for Greenland, finding that ice mass loss accelerated over the last two decades, and that melting ice-sheets will be a dominant contributor to sea level rise if that trend continues.