Bloomberg: Old-growth forests once studded with pine, hemlock and fir trees are dying across the western U.S. and Canada at double the rate of a half-century ago in what scientists are blaming on climate change. Hobbled by rising temperatures, more frequent drought and a bark beetle infestation, 200-year-old forests from California to British Columbia are becoming more sparse, losing trees faster than they are replacing them, U.S. Geological Survey researcher Phillip van Mantgem said. The …