Recent studies show that trees have a relatively small buffer to protect them from water stress. According to the research they've done, the increase in temperatures worldwide have put as much as 70 percent of our planet's trees in danger. There are other factors as well including urban creep, pollution, drought (of course), but I was told that temp is the big one because it is not localized and is effecting botanical life everywhere.
There's a ton we still do not know yet and many, many factors involved. We haven't had one of these threads in a little while and I thought his analysis was pretty interesting without being alarmist. So, I thought I would parse it out. Give it a listen.
Here's a print version of the story though with less info.