Tag Archives: antarctic

Ice Loss at Poles Is Increasing, Mainly in Greenland

From NASA:

PASADENA, Calif. – An international team of experts supported by NASA and the European Space Agency (ESA) has combined data from multiple satellites and aircraft to produce the most comprehensive and accurate assessment to date of ice sheet losses in Greenland and Antarctica and their contributions to sea level rise.

In a landmark study published Thursday in the journal Science, 47 researchers from 26 laboratories report the combined rate of melting for the ice sheets covering Greenland and Antarctica has increased during the last 20 years. Together, these ice sheets are losing more than three times as much ice each year (equivalent to sea level rise of 0.04 inches or 0.95 millimeters) as they were in the 1990s (equivalent to 0.01 inches or 0.27 millimeters). About two-thirds of the loss is coming from Greenland, with the rest from Antarctica.


From the abstract of the paper:

We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth’s polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year?1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year?1 to the rate of global sea-level rise.

The melting since about 1992 to the present has contributed to about 0.44 inches of sea level rise (about a fifth of the sea level rise over that period, and there was sea level rise prior to 1992 as well). The main outcome of this study is to clean up the predictions from previous models with much better data and to narrow down the best predictions for future melting. Also, the pace of ice loss now is greater than it was at the beginning of the study period, 20 years ago. Greenland is losing ice about 500% faster now than it was in the early 1990s, while Antarctica is losing ice at about the same rate now as it was then.

UPDATE: See also this post from the LA Times

Shepherd, A., Ivins, E., A, G., Barletta, V., Bentley, M., Bettadpur, S., Briggs, K., Bromwich, D., Forsberg, R., Galin, N., Horwath, M., Jacobs, S., Joughin, I., King, M., Lenaerts, J., Li, J., Ligtenberg, S., Luckman, A., Luthcke, S., McMillan, M., Meister, R., Milne, G., Mouginot, J., Muir, A., Nicolas, J., Paden, J., Payne, A., Pritchard, H., Rignot, E., Rott, H., Sorensen, L., Scambos, T., Scheuchl, B., Schrama, E., Smith, B., Sundal, A., van Angelen, J., van de Berg, W., van den Broeke, M., Vaughan, D., Velicogna, I., Wahr, J., Whitehouse, P., Wingham, D., Yi, D., Young, D., & Zwally, H. (2012). A Reconciled Estimate of Ice-Sheet Mass Balance Science, 338 (6111), 1183-1189 DOI: 10.1126/science.1228102

Photo of icebergs in Disko Bay, Greenland from NASA

Increase in Antarctic Sea Ice

One of the most commonly winged-about facts of Earth’s climate change we hear from science denialists is that sea ice in the Antarctic is increasing, therefore, there is no global warming. The fact that every other measurement of temperature and ice-osity indicates warming and melting would make a normal person think of the Antarctic situation as odd, and seek explanations, but somehow this logic does not emerge in the minds of the denialists. It has been suspected, and increasingly confirmed, for some time that the increase in sea ice in the Antarctic is the result of changes in wind patterns that cause a local increase in ice while at the same time the planet warms. New research from NASA and the British Antarctic Survey adds to this understanding. From a NASA press release:

NASA and British Antarctic Survey scientists have reported the first direct evidence that marked changes to Antarctic sea ice drift caused by changing winds are responsible for observed increases in Antarctic sea ice cover in the past two decades. The results help explain why, unlike the dramatic sea ice losses being reported in the Arctic, Antarctic sea ice cover has increased under the effects of climate change.

Research scientists Ron Kwok of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and Paul Holland of the Natural Environment Research Council’s British Antarctic Survey, Cambridge, United Kingdom, used maps created by JPL from more than five million individual daily ice-motion measurements. The data, captured over a period of 19 years by four U.S. Defense Meteorological satellites, show, for the first time, long-term changes in sea ice drift around Antarctica.

“Until now, these changes in ice drift were only speculated upon, using computer models of Antarctic winds,” said Holland, lead author of the study published this week in the journal Nature Geosciences. “This study of direct satellite observations shows the complexity of climate change. The total Antarctic sea ice cover is increasing slowly, but individual regions are actually experiencing much larger gains and losses that are almost offsetting each other overall.

“We now know that these regional changes are caused by changes in the winds, which, in turn, affect the ice cover through changes in both ice drift and air temperature,” he continued. “The changes in ice drift also suggest large changes in the ocean surrounding Antarctica, which is very sensitive to the cold and salty water produced by sea ice growth.”

Holland said sea ice around Antarctica is constantly being blown away from the continent by strong northward winds. “Since 1992, this ice drift has changed,” he said. “In some areas, the export of ice away from Antarctica has doubled, while in others it has decreased significantly.”

Sea ice plays a key role in Earth’s environment, reflecting heat from the sun and providing a habitat for marine life. At both poles, sea ice cover is at its minimum during late summer. However, during the winter freeze in Antarctica, this ice cover expands to an area roughly twice the size of Europe. Ranging in thickness from less than three feet (a meter) to several meters, the ice insulates the warm ocean from the frigid atmosphere above.

This new research also helps explain why observed changes in the amount of sea ice cover are so different in the two polar regions. The Arctic has experienced dramatic ice losses in recent decades, while the overall ice extent in the Antarctic has increased slightly. However, this small Antarctic increase is actually the result of much larger regional increases and decreases, which are now shown to be caused by wind-driven changes. In places, increased northward winds have caused the sea ice cover to expand outwards from Antarctica. In contrast, the Arctic Ocean is surrounded by land, so changed winds cannot cause Arctic ice to expand in the same way.

“The Antarctic sea ice cover interacts with the global climate system very differently than that of the Arctic, and these results highlight the sensitivity of the Antarctic ice coverage to changes in the strength of the winds around the continent,” said Kwok.

Climate change has had contrasting impacts across Antarctica in recent decades. The Antarctic Peninsula has warmed as much as anywhere in the Southern Hemisphere, while East Antarctica has shown little change or even a small cooling around the coast. The new research improves understanding of present and future climate change. The authors note it is important to distinguish between the Antarctic Ice Sheet – glacial ice – which is losing volume, and Antarctic sea ice – frozen seawater – which is expanding.

The research was funded by NASA and the Natural Environment Research Council.