ARCTIC SPRING FALLS WEEK BEFORE IT DID DECADE AGO.

Byline: Associated Press 

Spring springs eight days earlier in the Arctic than it did a decade ago, according to satellite measurements of vegetation coverage.

The measurements, recently analyzed by climatologists, suggest that plant cover appears earlier in the year, grows lusher and sticks around longer in northern climes than it used to.

Though there is no way to determine whether the shift is natural or man-made, the trend may be an early sign of human-caused global warming.

``It's enough to make you believe that something might well be happening,'' said Terry Chapin, an ecologist at the University of California at Berkeley.

Climatologists analyzed vegetation data from three weather satellites operated by the National Oceanographic and Atmospheric Administration. 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 during the peak of the growing season by 10 percent over the period, and stayed around about four days longer in the fall.

The analysis, published in the current issue of the journal Nature, isn't the first indication that things are heating up in the Arctic. But it is the first study to show an ecological response to climate change over a broad region.

The effect has been observed between 45 degrees and 70 degrees north, a band stretching from the latitude of Minneapolis to northern Alaska. It is especially pronounced in the high Arctic and in the interior regions of Canada and Siberia. That 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 Nature paper. ``I don't think I'm ready to say that global warming is upon us.''

Myneni is a climatologist at Boston University.