Forests Dying Two Times Faster, Thanks to Global Warming

Red fir, Sequoia National Park, California.

Photo: Nate Stephenson / U.S. Geological Survey

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Trees are dying at more than twice the rate they were just a few decades ago, and rising temperatures is most likely to blame, according to a new report published in Science by federal scientists working with the U.S. Geologic Survey.

The death rate is not limited to a single species or region, but was described as "pervasive" across all forest types, all elevations, in trees of all sizes. Pines, firs, hemlocks and other kinds of trees all showed the same "worrying" decline.

The end result could be "substantial changes in Western forests," according to the report's lead co-author, Phil van Mantgem. Think more wildfires, fewer wildlife species and forests as sources of the atmospheric carbon that causes global warming, not sinks.

In other words, the very problem causing these trees to die will be enhanced by the fact of their dying. That, folks, is what scientists cause a positive feedback loop, and it's one of the most terrifying aspects of global warming. Force too many of these feedback loops, and you get a runaway global warming scenario that no carbon taxes or energy efficiency improvements will counteract.

In this case, the feeback is very tangible: Forests lose trees faster than they grow back.

And it all traces back to global warming, which in the West has resulted in a 1-degree temperature increase over recent decades -- enough to cause a longterm reduction in the snowpack, increase the length of the summer drought and create conditions hospitable to pests like the bark beetle. Those conditions, in turn, are stressing trees.

"Tree death rates are like interest on a bank account - the effects compound over time," making forests susceptible to "sudden, extensive die-back," Nate Stephenson, the lead co-author, said in a prepared statement. "That," he said, "may be our biggest concern. Is the trend we're seeing a prelude to bigger, more abrupt changes to our forests?"

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