Greenland cools as world warms

Greenland is significantly cooler now than it was 40 years ago.

While scientists report warming trends in many parts of the globe, it seems this northern polar region has been moving in the other direction.

The finding is based on an analysis of historical meteorological data collected by Danish researchers.

It shows that during the period 1958 to 2001 average temperatures in the southern part of the island fell by 1.29 C. Sea-surface temperatures in the Labrador Sea also fell.

Globally, temperatures have risen over this period (+0.53 C) and in Greenland itself scientists have recently reported fairly dramatic thinning of the island's ice sheet.

But Dr Edward Hanna, from the Institute of Marine Studies at the University of Plymouth, UK, said that, as with all climate science, a fuller picture emerges when long-term data are taken into account.

Climate phenomenon

"It really depends on what timescale you are looking at," he told BBC News Online.

"Certainly in the late 1990s, there was some warming but that's just over a very short period. There are a lot of natural cycles in regional climate and if you take a longer trend over the last 40 or 50 years then there has been a statistically significant cooling, particularly in south-western coastal Greenland."

Dr Hanna together with Dr John Cappelen, of the Danish Meteorological Institute in Copenhagen, present their Greenland analysis in the journal Geophysical Review Letters.

It looks at data collected at eight stations. The cooling trend, they believe, is associated with an increased phase of the North Atlantic Oscillation (NAO) that has been observed over the past 35 years.

The NAO is a natural and recurring pressure pattern that has a profound impact on the weather experienced in the North Atlantic region - at the moment bringing milder, wetter winters to Northern Europe.

Hanna and Cappelen believe the NAO is likely linked with temperature reductions along the Greenland coast and is responsible for slowing the island's ice melting rate, in contrast to evidence of global warming.

Plane study

"And in fact, I've just been looking at the 2002 data and that appears to show a tailing off of the recent warming," Dr Hanna said.

He added: "I think the message from all this is that global warming is not a uniform process and you do get regional disparities."

Greenland covers more than two million square kilometres and 85% of the island is covered by ice, some of which is over three kilometres thick.

Concerns about warming in the region during the 1990s first came to the public's attention with a US space agency (Nasa) study which flew aircraft equipped with laser altimeters over the island to measure the profile of the ice.

Nasa found the ice had lost up to five metres in thickness over a five-year period. Other, more recent studies have continued to document a rapid thaw.

Greenland is important to climate studies because, having grounded ice, any significant melting would raise sea levels - by 6-7 metres if it were all to go.

INTERNET LINKS:
Geophysical Research Letters
Institute Of Marine Studies, University Of Plymouth
Nasa - Airborne Topographic Mapper
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