No Precedent In Past 11,000 Years For Larsen B Ice Shelf Collapse

[hatrack]

The collapse of a huge ice shelf in Antarctica in 2002 has no precedent in the past 11,000 years, according to a study to be published today that points the finger at global warming. Measuring some 3,250 sq km in area and 220m thick, the Larsen B iceshelf broke away from the eastern Antarctic Peninsula in 2002, eventually disintegrating into giant icebergs.

By chance, a US-led team of geologists had gathered a rich harvest of data around the ice shelf just before the spectacular collapse, including six cores that had been drilled into marine sediment. The cores contain the remains of plankton and algae imbedded in layers of minerals, and their radiocarbon and oxygen isotopes provide clues about ice cover and climate change over the millennia.

The researchers, reporting in Nature, the British science weekly, say that since the end of the last Ice Age, some 11,000 years ago, the ice shelf had been intact but had slowly thinned, by several dozen metres. Its coup de grace came from a recent but decades-long rise in air temperature, they say.

"The modern collapse of the LIS-B (Larsen B iceshelf) is a unique event within the Holocene," they write. "The LIS-B eventually thinned to the point where it succumbed to the prolonged period of regional warming now affecting the entire Antarctic Peninsula region."

EDIT

http://www.theaustralian.news.com.au/common/story_page/0,5744,16149199%255E30417,00.html

[whistle]

1. Is the sun expanding?

[skids]

2. Actually, we are at the low end...

...of the dominant 11 year solar power output cycle right now. However in 2002, that would have been more in the middle.

[Massacure]

3. The sun is getting hotter, but on a time scale of millions of years.

Global warming has been going on for only 100.

[bemildred]

4. A good question.

That is a factor over long periods. Moderation of CO2 in the atmosphere is one of the main mechanisms of temperature equilibrium on the planet, and the fraction of CO2 in the atmosphere is already quite small, which means over geological time things are likely to get hot because we cannot remove much more CO2 to cool things down, i.e. to decrease the greenhouse effect.

Human activity is, of course working against that, making it worse.

Carbon Dioxide Role In Past Climate Revealed

Researchers at the British Antarctic Survey (BAS) and the University of California, Santa Cruz have discovered that Earth's last great global warming period, 3 million years ago, may have been caused by levels of CO2 in the atmosphere similar to today's.

Reporting this week in a leading Earth Science journal, Geochemistry Geophysics Geosystems, the scientists describe how they tested two widely held ideas that attempted to explain the balmy conditions on Earth at that time. Their findings clearly demonstrate that studying past climates can help us to understand the likely impact of greenhouse gas emissions and global warming.

BAS Principal Investigator Dr Alan Haywood said, 'There are two schools of thought about past warm intervals. Many scientists suggest that they were caused by ocean currents (like the Gulf Stream) moving greater amounts of warm water from the tropics to the polar regions. Others speculate that increased levels of CO2 in the atmosphere initiated warming all over the planet. We used the latest supercomputing technology combined with chemical analysis of seabed sediments to make a sophisticated reconstruction of past sea temperatures. If the warming was caused by ocean currents, we would expect to see cooling at the tropics and warming at the poles. Conversely, if CO2 was the cause then we would expect both the tropics and the poles to warm. The sea temperature pattern we found points the finger squarely at CO2 rather than the ocean currents. This is a real breakthrough for those of us investigating past climate -- we've made a major contribution to a long standing argument and our findings are critical to understanding how climate may respond to emissions of greenhouse gases in the future'.

Clues to past sea-surface temperature come from tiny marine algae that live near the surface. They produce chemicals called alkenones that record the sea temperature. When the algae die they sink and become part of the seabed. Therefore, a record of past sea temperatures is stored within the sediments. Sea-surface temperatures were also predicted using a climate model running on a sophisticated supercomputer based at Manchester. This is capable of billions of calculations per second.

http://www.sciencedaily.com/releases/2005/04/050425105901.htm