科学美国人60秒:Forest Die-Offs Alter Global Climate 'Like El Nino'

Climate change may be partly to blame for the massive die-off of pine trees in the western U.S. But it works the other way, too: forest die-offs can alter the global climate. 

"I like thinking of this as a parallel to something like El Nino." Abigail Swann, an ecological climatologist at the University of Washington. "We think these are also going to have climate impacts far away from where those forests are dying. So it's going to ricochet in other places around the globe."

To model those 'ricochet' effects, Swann and her colleagues used climate simulations to wipe out forests and replace them with grasslands, in the western US, the Amazon, or both. They found that losing forests in one part of the globe does indeed affect climate very far away. "And that could be negative in a lot of places, it could be bad for the ecosystems, but you could come up with scenarios where it makes the conditions a little bit better." 

For example, killing off trees in western North America leads to cooler temps globally. That outcome means lower productivity in Siberian forests—a negative. It also dries up forests in the Carolinas—another negative. But conditions will get wetter in eastern South America—a positive for the forests there. The results are in the journal PLOS ONE. [Elizabeth S. Garcia et al, Synergistic ecoclimate teleconnections from forest loss in 2 different regions structure global ecological responses]

One surprise, though, was that when researchers erased forests in both the Amazon and the western U.S.—it had an uNPRedictable, synergistic effect on global climate. "It suggests that if we were to think about forest management around the globe, we should manage in a coordinated manner rather than independent entities. Because the climate response to these changes in forest cover is going to be a function of all of them happening at the same time." 

We do do that to some extent—like managing tropical deforestation through the U.N. But this study suggests we need to keep it up, and do even better, if we want to see the global forest for the trees.

—Christopher Intagliata