digital elevation models for Greenland and Antarctica
August 21, 2014

Scientists See Record Decline In Greenland And Antarctic Ice Sheets

April Flowers for - Your Universe Online

Data from the European Space Agency's (ESA) CryoSat-2 spacecraft has been used to map elevation and elevation changes in both Greenland and Antarctica by a team of researchers from the Alfred Wegener Institute (AWI) in Germany.

The new maps, which are the most complete to ever be created from a single satellite mission, reveal the ice sheets are losing volume at an unprecedented yearly rate (approximately 500 cubic kilometers). The study findings and maps were recently published in The Cryosphere.

"The new elevation maps are snapshots of the current state of the ice sheets. The elevations are very accurate, to just a few meters in height, and cover close to 16 million km2 (6.2 million square miles) of the area of the ice sheets. This is 500,000 square kilometers (193,000 square miles) more than any previous elevation model from altimetry", said Dr. Veit Helm, glaciologist at AWI.

The research team analyzed data retrieved from the CryoSat-2's altimeter SIRAL. Satellite altimeters use radar or laser pulses sent towards Earth to measure the height of an ice sheet. The signals reflect off the surface of the sheet and the surrounding water to be recaptured by the satellite. Just over a year's worth of data — including 7.5 million elevation measurements for Greenland and 6.1 million for Antarctica collected in 2012 — allowed the team to precisely determine the elevation of single glaciers and create the detailed maps.

The maps illustrate more than just the present highs and lows of the ice sheets. They also reveal how the elevation has changed between 2011 and 2014. Ice sheet mass is gained through snowfall and lost through melting and accelerating glaciers that push ice from the interior of the sheet to the ocean. Understanding how ice thickness across Greenland and Antarctica has changed is vital according to the research team in order to model ice movements and understand exactly how much ice sheets contribute to rising sea levels.

The elevation change maps required 200 million data points for Antarctica and 14.3 million for Greenland, collected over the three year period. They found that the Greenland ice sheet alone is reducing in volume by 375 cubic kilometers per year. Combined, the two ice sheets are declining at the rate of 500 cubic kilometers per year, the highest rate of decline seen since altimetry satellite records began two decades ago. Since 2009, the team says that the annual contribution of the ice sheets to sea level rise has doubled.

"When we compare the current data with those from the ICESat satellite from the year 2009, the volume loss in Greenland has doubled since then. The loss of the West Antarctic Ice Sheet has in the same time span increased by a factor of 3. Combined the two ice sheets are thinning at a rate of 500 cubic kilometers per year. That is the highest rate observed since altimetry satellite records began about 20 years ago," said AWI glaciologist Prof. Dr. Angelika Humbert. The East Antarctica sheet is gaining in volume, but not at a rate that compensates for the West's losses.

Greenland's Jakobshavn Isbae (Jokobshavn Glacier) and Antarctica's Pine Island glacier (PIG) are the two areas found to have the largest elevation changes. Jakobshavn is moving ice into the ocean at a faster rate than any other ice-sheet glacier, while PIG has been thinning rapidly in recent years.

Mark Drinkwater, ESA’s CryoSat Mission Scientist, noted, “These latest results offer a critical new perspective on the recent impact of climate change on the large ice sheets. Whilst CryoSat provides essential continuity in an ice sheet elevation record dating back to ESA’s ERS satellite data from the early 1990s, these results also highlight its design capability to capture regional patterns in the rate of change."

“This is particularly evident in parts of the Antarctic peninsula, where some of the more remarkable features add testimony on the impact of sustained peninsula warming at rates several times the global average.”