Global Warming Killing American Trees

A new report in Science journal suggests trees in western US are dying due to climate change:

http://news.bbc.co.uk/go/pr/-/1/hi/sci/tech/7841030.stm

The scientists examined 59,000 trees more than 200 years old. The mortality rate was found to have doubled since 1955. Factors like insect attacks and air pollution were ruled out. Climate warming was the dominant factor. Over a 30 year period from the 1970's, mean temperatures in western US had increased around 0.4 degrees C per decade. The team also believe that a feedback loop could develop, and the forests are vulnerable to sudden, more extensive dieback.