The American West is losing its autumn colours as global warming begins to bite and there is far more at stake than iconic scenery. Aspen, the white-barked trees with golden leaves that gave their name to the famed Colorado ski resort, have been dying off across the Rocky Mountain states. The die-off is puzzling but some foresters point to climate change. This disaster coincides with beetle outbreaks that have laid waste to millions of acres of pine and spruce forest in the American and Canadian west. They too have been linked to warmer winters since extremely cold temperatures are needed to kill the insects. Recent droughts and other factors linked to global warming are seen as likely causes for 'sudden aspen decline', or SAD, so named because it can strike a forest so quickly. "Assuming climate predictions are true, it probably is a sign of things to come," said Jim Worrall, forest pathologist with the US Forest Service. Colorado acreage ravaged by SAD quadrupled from 2006 to 2008 to more than 850 square miles. The syndrome has also struck in Utah, Wyoming and Idaho, where researchers suggest a warmer, drier West may all but eliminate aspen from the Rocky Mountains by the end of the century.