Arctic warming gathers pace

Measurements of glaciers formed part of the review

By environment correspondent Alex Kirby

US researchers say they have found evidence of rapid warming in parts of the Arctic over the last 30 years.

At the end of the 20th Century, they say, Arctic temperatures were the warmest for four centuries.

And the warming was accompanied by other environmental changes, which appear to be at least partly caused by human activity.

The researchers say their findings support climate models which predict that the Arctic will be one of the first regions to respond to a global warming trend.

But they say it is increasingly hard to obtain reliable climate data from the Arctic.

Pieced together

The principal author of their report, published in a Dutch journal, Climatic Change, is Mark Serreze, of the National Snow and Ice Data Center at the University of Colorado at Boulder.

Wildlife is vulnerable to change

He said: "We had the pieces of the puzzle gathered, and we synthesised them to give us the best picture of what is going on right now in the Arctic."

The research involved reviewing more than 100 separate studies covering a variety of components of Arctic change going back centuries.

It looked at a range of variables: air temperatures, atmospheric circulation, precipitation data, snow cover, and snow depth records.

It also included sea ice measurements, ocean structure data, permafrost temperature observations, glacier mass balances, plant growth, and carbon flux measurements.

Research cutbacks

In parts of the Arctic, the researchers found, temperatures have risen significantly in a very short time.

Parts of Alaska and northern Eurasia, for example, have warmed by nearly six degrees Celsius (11 degrees Fahrenheit) in the winter months since the early 1970s.

The Arctic is changing fast

Dr Serreze said: "We have climate evidence from the past four centuries gleaned from ice cores, lake cores and tree rings that don't show nearly as dramatic warming, putting the modern record into context."

He also gave a warning about the increasing difficulty of obtaining climate data from the Arctic, because of cutbacks in research. Some hydrometeorological stations have been closed and other climate networks scaled back in Canada and Russia, Dr Serreze said.

Russia had from 1950 continuously maintained up to three drifting ice stations as part of the North Pole Drifting Program.

This took weather readings and atmospheric soundings, and recorded solar radiation and snow condition data. But it was closed in 1991. Dr Serreze said Canada was also cutting back on the amount of data gathered from its high-latitude climate stations by going over to automated systems.

"We may be able to take up some of the slack by recording similar data with satellites," said Dr Serreze. "But we are losing the value of long-term data continuity.

"Our study validates climate-model results that predict the Arctic will be among the first regions on earth to respond to a global warming trend. Given what we are seeing, continued monitoring of this region is crucial."

Scepticism persists

Some researchers still doubt that human activities are inducing rapid climate change.

They highlight the inconsistencies between the temperature records taken at the Earth's surface, which show rapid warming over the last century, and the data produced by satellite and balloon studies.

These show little if any warming, in the last two decades, of the low to mid-troposphere - the atmospheric layer extending up to about 8km from the Earth's surface.

Climate models generally predict that temperatures should increase in the upper air as well as at the surface if increased concentrations of greenhouse gases are causing the warming recorded at ground level.