In western North America, huge swaths of forested areas may become unsuitable for trees owing to climate change, say researchers. In the Rocky Mountains, estimates hold that by 2050, about 15% of the forests would not grow back if felled by fire because the climate would no longer suit them. In Alberta, Canada, about half of existing forests could vanish by 2100. In the south-western US, which is experiencing a "megadrought", as much as 30% of forests are at risk of converting to shrubland or another kind of ecosystem.