National Public Radio: Warming global temperatures could cause massive tree die-offs. That’s the gloomy conclusion of a new study by scientists at the University of Arizona. The study addressed a fairly basic question: Do warmer temperatures make trees more susceptible to drought? It might seem surprising that scientists don’t already know the answer to that question. But biologist David Breshears of the University of Arizona says there’s a lot that scientists don’t know about trees. “Like, what does …