Early spring for the North
Satellite study offers new evidence of global warming
from Northern News Services
NNSL (Apr 21/97) - Spring springs eight days earlier in the Arctic than it did a decade ago, according to satellite measurements of vegetation cover.
The measurements suggest that plant cover appears earlier in the year, grows more lush and sticks around longer in northern climes than it used to.
Though there is no way to determine whether the shift is natural or the result of industrial pollution, it could be a sign of global warming.
"It's enough to make you believe that something might well be happening," said ecologist Terry Chapin of the University of California at Berkeley.
Climatologists analysed data from three U.S. weather satellites. They found that in 1991 spring began in many Northern regions about a week earlier than it had a decade before.
The researchers also found that plants increased the vigor of their photosynthesis by 10 per cent during the growing seasons, and stayed about four days longer in the fall.
The analysis, published in the journal Nature, isn't the first indication of Arctic climate change. But it is the first study to show an ecological response over a broad region.
The effect has been observed between 45 degrees and 70 degrees north and is especially pronounced in the High Arctic and in the interior regions of Canada and Siberia. The pattern is consistent with what computer models of human-induced global warming predict.
"These are all manifestations of a greenhouse effect if you will, but consistent is the word," said Ranga Myneni, the lead author of the xxxNature paper. "I don't think I'm ready to say that global warming is upon us."
The researchers measured plant activity by looking at the color of sunlight reflected off the ground. Reflections from leafy surfaces have a different color than light reflecting off bare ground. Satellites can detect that shift.
"Scientifically, it's a marvellously provocative piece of evidence," said Inez Fung, a climatologist at the University of Victoria.
The satellite data add to a wealth of data suggesting warming in the Far North. Arctic weather stations have detected rising temperatures for decades, permafrost is retreating in many regions and snowmelt comes earlier each year.
Also, a study published last year in Nature by Charles Keeling of the Scripps Institution of Oceanography showed that plants in the Far North are producing and using more carbon dioxide than they used to, suggesting an increase in biological activity.
The Arctic warming illustrates an important aspect of climate change, scientists said. Even if the average warming over the entire globe due to greenhouse gases is not very great, the effects on specific regions at certain times of the year could be profound.
The Arctic temperature increase seems to be concentrated in March, though nobody knows why or what is causing it.