Signs of warming continue in the Arctic with a decline in sea ice, an increase in shrubs growing on the tundra and rising concerns about the Greenland ice sheet.

"There have been regional warming periods before. Now we're seeing Arctic-wide changes," James Overland, an oceanographer at the Pacific Marine Environmental Laboratory in Seattle, said Thursday.

For the past five years, it was at least 1.8 degrees Fahrenheit above average over the Arctic over the entire year, he said.

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The new "State of the Arctic" analysis, released by the National Oceanic and Atmospheric Administration, also reports an increase in northward movement of warmer water through the Bering Strait in 2001-2004. This may have contributed to a continuing reduction of sea ice.

During that time, there were record lows in sea ice coverage in the region, Overland said. This year there was more normal coverage in the Bering area but a record low on the Atlantic side of the Arctic.

• Click here to read the NOAA 'State of the Arctic' report (pdf).

In the past when such a shift occurred, there would have been no net loss of ice overall, just a change in where there was a smaller amount. Now, however, there is both the shift and an overall net loss of ice, he said.

Indeed, the report said Arctic sea ice coverage this past March was the lowest in winter since measurements by satellite began in the early 1970s.

• Click here to read a report on the decline in the survival rate of Alaskan polar-bear cubs from the U.S. Geological Survey.

Jacqueline A. Richter-Menge of the Cold Regions Research and Engineering Laboratory in Hanover, N.H., said the sea ice decline is now being observed in both winter and summer.

The study was designed to assess the overall impact of climate change in the Arctic and will be updated annually. It was compiled by researchers from the United States, Canada France, Germany, Poland, Norway, Sweden and Russia, she said.

In addition, 2007 has been designated the International Year of the Arctic, with intense scientific study of the region planned.

There have been many changes over the Arctic land areas, too, said Vladimir E. Romanovsky, a professor at the geophysical institute of the University of Alaska. These include changes in vegetation, river discharge into the Arctic Ocean, glaciers and permafrost.

The tundra is becoming greener with the growth of more shrubs, he said. This development is causing problems in some areas as herds of reindeer migrate.

At the same time, there is some decrease in the greening of the northern forest areas, probably due to drought. The glaciers are continuing to shrink and river discharge into the Arctic Ocean is rising, Romanovsky said.

There has been a significant warming of the permafrost over the past 30 years, he added.

Much of the damage to the permafrost soil can be blamed on human construction activities and fires, he said. In many areas, this frozen ground is close to the melting point and soon could begin to thaw.

Overland said the changes are affecting wildlife in the Arctic. Those in the middle levels of the ocean, such as pollock, seem to do well; those on the surface ice or the sea floor, such as walrus or crabs, are not coping as well.

"We're seeing a lot of indicators of climate change in the Arctic and that may be an indicator for change in other parts of the world," Overland said.

Most of the heating from the sun comes to the equator and subequatorial regions, and a lot of heat leaves by radiation from Arctic, he said.

"The temperature difference between the Arctic and equator drives all of our weather," Overland said. If the Arctic warms up and that difference is reduced, weather could change, though people remain unsure about the effect.