* Arctic sea ice drops to third-lowest level
* Vanishing Arctic ice forces walruses onto land
By Deborah Zabarenko, Environment Correspondent
WASHINGTON, Sept 15 (Reuters) - So far, 2010 is tied for the warmest year on record, and Arctic sea ice reached its third-lowest level, prompting thousands of walruses to haul themselves out of ice-starved waters, U.S. scientists said on Wednesday.
The first eight months of the year match the record set for the same period in 1998 for the highest combined land and ocean surface temperatures worldwide, at 58.5 degrees F (14.7 C), 1.21 degrees F (0.67 degrees C) above the 20th century average, the U.S. National Climatic Data Center said in a statement.
Temperatures for the northern hemisphere summer -- June through August -- were the second-warmest globally, after 1998, the center said.
Most parts of the globe were hotter than average, with the most prominent warmth in eastern Europe, eastern Canada and parts of eastern Asia. Australia, central Russia and southern South America were cooler than average.
Britain had its coolest August since 1993, according to the U.K. Met Office, while China was 2 degrees F (1.1 degree C) above the 1971-2000 average, the warmest August since 1961, the Beijing Climate Center reported.
In the Arctic, sea ice cover appeared to hit its lowest point for the year on September 10, according to the U.S. National Snow and Ice Data Center.
This year's Arctic ice cover is the third-lowest since satellites started measuring in 1979, the center said in a statement. This is less ice than at 2009's low point, but above the amount seen in 2008 and 2007.
That's still less than the long-term average and well outside the range of natural variability, the center said.
WALRUSES ON SHORE
At its lowest level, Arctic sea ice covered 1.84 million square miles (4.76 million square kilometres), about 240,000 square miles (630,000 square kilometres) above the record low of 2007.
This is only the third time satellites have shown Arctic ice extent dropping below 1.93 million square miles (5 million square kilometres).
The loss of Arctic sea ice has caused thousands of Pacific walruses to come up onto land, the conservation group World Wildlife Fund said, citing U.S. Geological Survey observations.
An estimated 10,000 to 20,000 walruses gathered onshore in Alaska in recent days, said Geoff York, an Arctic biologist with World Wildlife Fund.
"When these animals get to shore, they're normally spread out across a pretty vast area of sea ice so they're not piled up in the 10s or 20 thousands of animals that we see happening now," York said by telephone.
Under normal conditions, walruses eat bottom-dwelling creatures in shallow water on the continental shelf, using sea ice as fishing platforms. Recently, sea ice has retreated past the shelf into areas of deep water, where walruses can't fish.
Risks include the long swim to land, sometimes as much as 400 miles (643.7 km); trampling in walrus stampedes -- they spook easily, like deer or cattle, York said -- and the threat of predation by polar bears.
However, having many walruses on shore may make it easier to get an accurate population estimate, said Chad Jay of the U.S. Geological Survey Alaska Science Center.
The current estimate, based on a 2006 aerial survey, is 130,000, but Jay said this is probably low because the survey skipped some areas. (Additional reporting by Yereth Rosen in Anchorage; Editing by Jerry Norton)
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