Lake sediments contain a record of Arctic temperatures
Arctic temperatures are now higher than at any time in the last 2,000 years, research reveals.
By Richard Black Environment correspondent, BBC News website Page last updated at 20:29 GMT, Thursday, 3 September 2009 21:29 UK
Changes to the Earth's orbit drove centuries of cooling, but temperatures rose fast in the last 100 years as human greenhouse gas emissions rose.
Scientists took evidence from ice cores, tree rings and lake sediments.
Writing in the journal Science, they say this confirms that the Arctic is very sensitive both to changes in solar heating and to greenhouse warming.
The 23 sites sampled were good enough to provide a decade-by-decade picture of temperatures across the region.
The result is a "hockey stick"-like curve in which the last decade - 1998-2008 - stands out as the warmest in the entire series.
"The most pervasive signal in the reconstruction, the most prominent trend, is the overall cooling that took place for the first 1,900 years [of the record]," said study leader Darrell Kaufman from Northern Arizona University in Flagstaff, US.
"The 20th Century stands out in strong contrast to the cooling that should have continued. The last half-century was the warmest of the 2,000-year temperature record, and the last 10 years have been especially dramatic," he told BBC News.
On average, the region cooled at a rate of 0.2C per millennium until about 1900. Since then, it has warmed by about 1.2C.
The research shows a long, slow cooling followed by an abrupt warming
Much debate on climate change has centred on the Mediaeval Warm Period, or Mediaeval Climate Anomaly - a period about 1,000 years ago when, historical records suggest, Vikings colonised Greenland and may have grown grapes in Newfoundland.
The new analysis shows that temperatures were indeed warmer in this region 1,000 years ago than they were 100 years ago - but not as warm as they are now, or 1,000 years previously.
"It shows that the Mediaeval Warm Period is real, and is... an exception from the general trend of cooling," commented Eystein Jansen from Bergen University in Norway, who was not involved in the research.
"It also shows there's lots of variability on the 100-year timescale, and that's probably more so in the Arctic than elsewhere."
Professor Jansen was a co-ordinating lead author on the palaeoclimate (ancient climate) chapter of the last Intergovernmental Panel on Climate Change (IPCC) assessment.
Arctic wobbles
The root cause of the slow cooling was the orbital "wobble" that slowly varies, over thousands of years, the month in which the Earth approaches closest to the Sun.
This wobble slowly decreased the total amount of solar energy arriving in the Arctic region in summertime, and the temperature responded - until greenhouse warming took over.
"The 20th Century is the first century for which how much energy we're getting from the Sun is no longer the most important thing governing the temperature of the Arctic," said another of the study team, Nicholas McKay from the University of Arizona.
The recent warming of the Arctic has manifested itself most clearly in the drastic shrinkage in summer sea-ice extent, with the smallest area in the satellite era documented in 2007.
As the Science study emerged, UN Secretary-General Ban Ki-moon was telling the World Climate Conference in Geneva that many of the "more distant scenarios" forecast by climate scientists were "happening now".
Earlier this week, Mr Ban visited the Arctic in an attempt to gain first-hand experience of how the region is changing.
"Scientists have been accused for years of scaremongering. But the real scaremongers are those who say we cannot afford climate action," he said in his Geneva speech, calling for world leaders to make bigger pledges of action in the run-up to December's UN climate summit in Copenhagen.
F6, Pine Island, glacier .. notes plus images .. thinning four times faster than 10 years ago .. surface rate dropping up to 16m a year .. surface down up to 90m since 1994 .. serious implications for sea-level rise .. British research in Geophysical Research Letters .. team led by Professor Duncan Wingham of University College London (UCL) .. calculations based on the rate of melting 15 years ago ice stream longevity adjusted from 600 years (calcs based on 15 yr old figures) to recent research 100 yrs .. loss rate fastest in centre, implications if continues glacier break-up could start to affect ice sheet further inland .. Professor Andrew Shepherd of Leeds University, centre melting would add about 3cm to global sea level .. (note: most of Bangladesh is 1m above sea level) .. NOTE: ice trapped behind it is about 20-30cm of sea level rise .. we don't really know what will happen as we destabilise or remove the middle of the glacier we don't know really know what's going to happen to the ice behind it .. unprecedented in this area .. known it's been out of balance for some time, "but nothing in the natural world is lost at an accelerating exponential rate like this glacier." .. large, multiple deep crevasses are sign parts of the glacier are moving rapidly .. West Antarctic .. 11-hour round-trip from Punta Arenas .. ice stream 20 miles wide, in places one mile, plus thick .. latest satellite data showing rate on surface drop level will add to the alarm among polar specialists.
Greenpeace, studying northwestern Greenland .. one, Professor Jason Box of Ohio State University, surprised by how little sea ice seen in the Nares Strait between Greenland and Canada .. set up time lapse cameras set up to monitor the massive Petermann glacier .. huge new cracks observed and expected a major part could break off imminently .. "The science community has been surprised by how sensitive these large glaciers are to climate warming. First it was the glaciers in south Greenland and now as we move further north in Greenland we find retreat at major glaciers. It's like removing a cork from a bottle."
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! WOW! BOWS TO OUR NATURE'S MAJESTY. PINE ISLAND GLACIER.
NASA MODIS image from Aug. 5, 2010, shows a large chunk of ice has broken away from Greenland's Petermann Glacier (iceberg is just to the right of center). Credit: NASA
Icebergs calving off of Greenland's glaciers are nothing new. In fact, the Canadian Ice Service [ http://ice-glaces.ec.gc.ca/ ] and the U.S. Coast Guard's International Ice Patrol [ http://www.uscg-iip.org/cms/ ] estimate that anywhere between 10,000 and 40,000 icebergs calve from the glaciers of western Greenland in a given year.
What is unusual, however, is the size of this new iceberg, which is more typical of Antarctic than Arctic waters.
The National Ice Center in Suitland, Md., tracks a number of massive icebergs [ http://www.natice.noaa.gov/products/south_icebergs_on_demand.html ] in the oceans surrounding Antarctica, some of which are truly monsters. One, known as D-15, is a little larger than the state of Rhode Island, and 33 are currently being tracked that are more than 10 nautical miles long on one axis.
The Canadian Ice Service, a federal agency that monitors ice hazards in the Northwest Passage and other summer shipping routes in northern Canadian waters, issued alerts last year about another massive "ice island" from Greenland -a 29-square-kilometre monolith that broke away in 2008 from the Petermann Glacier on the island's northwest coast -as it floated south toward Canada's Arctic shores.
Officials were concerned at the time about the potential risk to cruise and cargo ships, but the Petermann Ice Island eventually eroded and broke into smaller pieces along the coast of Baffin Island.
The collapse of several Arctic ice shelves in recent years has kept the Canadian Ice Service on alert for possible threats to ships and oil exploration activity.
In 2005, a 66-square-kilometre chunk of the Ayles Ice Shelf on Ellesmere Island's northern coast broke free and began drifting south. Federal scientists kept a watch on the resulting Ayles Ice Island as it tracked a worrisome route toward the Beaufort Sea.
But in August 2007, the five-by-15-kilometre slab turned down a dead-end channel between Meighen and Axel Heiberg islands, where it was expected to slowly break up over years and become an anonymous part of the Arctic pack ice.
So, what will become of this latest iceberg? Chances are that the majority of the iceberg will remain inside its fjord [ http://en.wikipedia.org/wiki/Fjord ] and become frozen in place this fall during the annual freeze up. Still, a large number of smaller icebergs are likely to break off from it and some of these should make it out into the Nares Strait, and from there be swept along with the currents into the northern portions of Baffin Bay.
The author, Capital Weather Gang's Brian Jackson, is a physical scientist at the National Ice Center, which is operated by the U.S. Navy, the National Oceanic and Atmospheric Administration, and the U.S. Coast Guard. Its mission is to provide snow and ice products and services to meet the nation's strategic, operations and tactical requirements.
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