Global warming doubles tree deaths in US

Global warming and the resulting drought have likely doubled the tree death rate over the past 30 years in old-growth forests in the western United States, according to a study released on Thursday.

Researchers said the accelerated forest loss could trigger an environmental domino effect on the region's wildlife and climate.

Temperatures in western US forests have increased on average more than 0.5 degrees C over the past 30 years, reducing snowfall accumulations, prolonging summer droughts and raising the insect population, including tree-killing bark beetles.