Is Global Warming Real? Evidence: Antarctic Ice

Global warming is in the news lately, with the media frenzy about Climategate and the Copenhagen conference. This hub is part of a series about the evidence for global warming.

Previous hubs dealt with global temperature records, declining snow cover, and the shrinking Arctic ice cap.

This hub examines global warming at the South Pole. It is a bit longer than earlier hubs, because Antarctica is so much more complicated than the Arctic.

If you want the short and sweet version, here it is:

• Western Antarctica has warmed significantly. The rest of Antarctica has seen little to no warming - which is in line with global warming predictions.
  
• Antarctic sea ice is increasing in area
• but the Antarctic ice sheet as a whole is getting thinner (even though some parts are getting thicker - I told you it was complicated) and
• Antarctic land ice is melting into the sea.

Now, if you want the nitty gritty, read on.

The ice at the North pole is in obvious decline. The evidence from the South Pole, however, is a little more complicated. Is the ice thickening? Shrinking? Both? Is it warming or cooling?

In fact, the Antarctic sea ice area has increased by about 100,000 square miles over the past few decades. But the land ice is melting more and more.

The 2001 IPCC Assessment on Global Climate Change, as well as many early climate models, predicted that Antarctica would not warm as fast as the rest of the globe. One reason for this is the nature of ocean currents at the Antarctic, which pull warm surface water down quickly, Another factor leading to less warming over the Antarctic continent is the hole in the Ozone, which affects wind patterns, diverting warmer air away from the interior. The National Snow and Ice Data Center has more information here.

However, there are definite signs of warming.

Most of the warming is due to warmer winters and longer summers. Parts of the continent are warming significantly, while others are not.

More info about the image above is available here.

The most drastic warming is seen on the Antarctic Peninsula, where average temperature has risen by approximately 2.5°C/4.5°F since monitoring started in the 1950s. Western Antarctica also shows significant warming. Temperatures in the interior of the continent, however, have increased somewhat less, with many stations showing no warming at all. A report just released by the Scientific Committee on Antarctic Research (SCAR) puts the warming over all of Antarctica at 0.2 degrees Celsius since the 19th century (more on that report below) - and most of that warming occurred before 1960.

While the overall trend of less warming predicted by the climate models seems to be borne out by observations, Antarctic ice seems to be losing mass.

In 2006, scientists from the University of Chicago analyzed data from the GRACE satellites, which measure small changes in the earth's gravitational field. They found significant loss of mass in Antarctica (Velicogna et al, Measurements of Time-Variable Gravity Show Mass Loss in Antarctica, Science Express March 2006).

An analysis of ice sheet losses in 2008 also found an overall loss of ice mass.(Rignot et al, Recent Antarctic ice mass loss from radar interferometry and regional climate modelling, Nature Geoscience 1, Jan 2008)

A new paper from the University of Texas, also looking at GRACE satellite data, indicates that the rate of ice loss has accelerated since 2006. (Chen et. al, Accelerated Antarctic ice loss from satellite gravity measurements, Nature Geoscience 2, Nov. 2009)

So - while sea Ice area has increased, the ice overall is getting thinner - even though it is also thickening in parts of Antarctica.

The report on Antarctic Climate Change and the Environment (AACE) (large PDF file), from The Scientific Committee on Antarctic Research was just released on December 2, 2009, and makes the following statements about the Antarctic:

• The Antarctic troposphere has warmed at 5 km above sea level, and the stratosphere above it has cooled over the last 30 years. This is what we would expect from warming caused by greenhouse gases. (ACCE p. xvii)
• "Warming has caused retreat of ice shelves on both sides of the Peninsula.... Removal of ice shelves has led to the speeding up of glacier flow from inland."
• Some formerly snow- and ice-covered islands are now increasingly snow-free during the summer.
  
• Glaciers on Heard Island reduced by 11% since the 1940s, and several coastal lagoons have formed there.
  
• On South Georgia, 28 of 36 surveyed glaciers are retreating, 2 are advancing, and 6 are stable.
  
• On Signy Island ice cover has reduced by around 40%.
• Of the 244 marine glaciers that drain the ice sheet and associated islands of the Antarctic Peninsula, 212 (87%) have shown overall retreat since 1953. The other 32 glaciers have shown small advances.
• The Amundsen Sea sector is the most rapidly changing region of the Antarctic ice sheet. Thegrounding line at Pine Island has retreated, and the Pine Island Glacier is now moving at speeds 60% higher than in the 1970s. The Thwaites Glacier and four other glaciers in this sector show accelerated thinning. Smith Glacier has increased flow speed 83% since 1992.
• The Pine Island and adjacent glacier systems are currently more than 40% out of balance, discharging 280 ± 9 Gt per year of ice, while they receive only 177 ± 25 Gt per year of new snowfall. The current rate of mass loss from the Amundsen Sea embayment ranges from 50 to 137 Gt per year, equivalent to the current rate of mass loss from the entire Greenland ice sheet, and making a significant contribution to sea level rise.
• The changes result from warming of the sea beneath the ice shelves connected to the glaciers.
• The ice sheet shows interior thickening at modest rates and a mixture of modest thickening and strong thinning among the fringing ice shelves. Increasing coastal melt is suggested by recent passive microwave data. (ACCE p. xviii)
• The waters around Antarctica have warmed more rapidly than oceans in the rest of the world. The changes are consistent with greenhouse gas forcing.(ACCE p. xix)

Further evidence of warming in Antarctica is the fact that Antarctic Hair Grass populations have increased by 25 times, and Antarctic Pearlwort has increased fivefold. These are the only two plants native to Antarctica, and they have spread rapidly over the past few years.

There's still more evidence in the next hub! Thanks for reading so far.