Wednesday, December 17, 2008

Arctic Ice Melt

Last week, the Sumpter Elementary 5th graders and I did two ice melt experiments.  The first experiment compared land-based ice melt with sea-based ice melt.  The latter takes about a third as long as the land-based ice melt.  With that in mind, note that overall the Arctic ice is melting very quickly.

Planet Ark reports:

Ice volume around the Arctic region hit the lowest level ever recorded this year as climate extremes brought death and devastation to many parts of the world, the U.N. weather agency WMO said on Tuesday. Although the world's average temperature in 2008 was, at 14.3 degrees Celsius (57.7 degrees Fahrenheit), by a fraction of a degree the coolest so far this century, the direction toward a warmer climate remained steady, it reported.

"What is happening in the Arctic is one of the key indicators of global warming," Michel Jarraud, Secretary General of the World Meteorological Organization (WMO), said. "The overall trend is still upwards." A report presented by Jarraud at a news conference showed Arctic ice cover dropping to its second lowest extent during this year's melt season since satellite measuring began in 1979. However, the Geneva-based agency said, "because ice was thinner in 2008, overall ice volume was less than in any other year." It added: "The season strongly reinforced the 30-year downward trend in the extent of Arctic Sea ice."

The dramatic collapse of a quarter of ancient ice shelves on Canada's Ellesmere Island in the north of the Arctic Ocean added to earlier meltdowns, reducing cover in the region from 9,000 square km (3,500 sqmiles) a century ago to just 1,000 sq kms.

The WMO said the slight slowdown in warming this year, an increase of 0.31C over the 14C of the base period 1961-90, against an average 0.43C for 2001-2007, was due to a moderate-to-strong La Nina in the Pacific in late 2007. "This decade is almost 0.2 degrees (Celsius) warmer compared to the previous decade. We have to look at it in that way, comparing decades not years," Peter Stott, a climate scientist at Britain's Hadley Center, which provided data for the WMO report, told Reuters in London.

We did an even more interesting experiment on how fast land-based ice sheets may melt.  We took three ice sheets: one with very small cracks, but essentially intact; one with significant cracks; and one with significant cracks with water that slips through them.  The third ice sheet (which to some extent might represent the reality of Antarctic ice sheets) melted in about 35 minutes, the second ice sheet took about 83 minutes, and the first ice sheet took nearly 360 minutes.  We concluded that estimates of ice melt based on largely intact ice would substantially underestimate the true rate of melting if there are in fact significant cracks that have water pooling and sliding down the cracks.

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