By Alister Doyle
OSLO (Reuters) - The area of ice in the Arctic Ocean has thawed to a record low, surpassing the previous 2007 minimum in a sign of climate change transforming the region, according to some scientific estimates.
"We reached the minimum ice area today (Thursday). It has never been measured less than right now," Ola Johannessen, founding director of the Nansen Environmental and Remote Sensing Center in Norway, told Reuters.
"It is just below the 2007 minimum."
The U.S. National Snow and Ice Data Center (NSIDC), widely viewed as the main authority on sea ice, has projected that the 2007 minimum extent is set to be breached next week. The summer thaw usually continues well into September.
Other scientists monitoring the ice interpret satellite data in slightly differing ways.
An ice chart compiled by the Danish Meteorological Institute (DMI) showed the ice extent had also just shrunk a fraction past the 2007 minimum. The DMI said it would defer to the NSIDC to judge when a record had been set.
Ice has been shrinking steadily in recent decades in the Arctic, threatening the livelihoods of indigenous peoples and wildlife. It is also helping to open an area rich in oil and gas and bringing the promise of new, shorter shipping routes.
"This is due to climate change," Nicolai Kliem, head of the ice service at DMI, said of the long-term decline in summer ice. Scientists project that summer sea ice could vanish completely in coming decades.
The retreat of the ice may be self-reinforcing. Ice reflects sunlight back into space and as it shrinks it exposes dark water that absorbs more heat, accelerating thawing.
Johannessen stressed his measurement was of the "area" of ice, now less than 4.0 million sq km (1.5 million sq miles), omitting the open water between ice floes.
The NSIDC prefers a bigger "extent", including such gaps, on the grounds that pools of meltwater that form on sea ice are hard to distinguish from open ocean.
Kliem said the ice was becoming more prone to melt because there was less of the hard, resilient ice that endures more than one year. The ice usually reaches a minimum in September before forming again as winter approaches and reaching a maximum in March.
"We had quite a big ice cover in March 2012, above average. But because there is little long-term ice it melts more quickly in summer," he said.
In a sign of widening interest in the polar region as a short-cut shipping route between the Pacific and the Atlantic, Beijing sent an icebreaker across the Arctic this summer to Iceland - the first Chinese vessel to cross the Arctic Ocean.
Nansen Centre -- http://arctic-roos.org/observations/satellite-data/sea-ice/ice-area-and-extent-in-arctic
Danish Meteorological Institute -- http://ocean.dmi.dk/arctic/icecover.uk.php
NSIDC -- http://nsidc.org/arcticseaicenews/
(Reporting by Alister Doyle; editing by Andrew Roche)