Globe and Mail: The death of old-growth forests in the western United States and Canada is increasing at a stunning rate, a troubling trend linked directly to global warming that could soon transform forests into carbon dioxide emitters rather than much-needed carbon sinks, a new study warns. Scientists have found that tree mortality has more than doubled in the last few decades regardless of elevation, forest type or tree size as pines, firs, hemlocks and other species are dying faster than new …