Massive forest die-offs threaten to accelerate global warming

An amazing article from the NYTimes:

Across millions of acres, the pines of the northern and central Rockies are dying, just one among many types of forests that are showing signs of distress these days.
From the mountainous Southwest deep into Texas, wildfires raced across parched landscapes this summer, burning millions more acres. In Colorado, at least 15 percent of that state’s spectacular aspen forests have gone into decline because of a lack of water.

The devastation extends worldwide. The great euphorbia trees of southern Africa are succumbing to heat and water stress. So are the Atlas cedars of northern Algeria. Fires fed by hot, dry weather are killing enormous stretches of Siberian forest. Eucalyptus trees are succumbing on a large scale to a heat blast in Australia, and the Amazon recently suffered two “once a century” droughts just five years apart, killing many large trees.

Thanks to recent research on the carbon cycle, we now know that half of the human emissions absorbed by carbon sinks -- in turn about half of the total anthropogenic CO2 -- is absorbed by the world's forests. CO2 has a fertilizing effect on many forest species, which -- for the moment -- has allowed the natural sinks to grow in efficacy as the human source has grown. Unfortunately, the heat that the CO2 brings with it threatens to unravel this critical carbon cycle decelerator:

 “A lot of ecologists like me are starting to think all these agents, like insects and fires, are just the proximate cause, and the real culprit is water stress caused by climate change,” said Robert L. Crabtree, head of a center studying the Yellowstone region. “It doesn’t really matter what kills the trees — they’re on their way out. The big question is, Are they going to regrow? If they don’t, we could very well catastrophically lose our forests.”

 How bad could this get? We don't have the science on that yet. But just as a yardstick of comparison, if forest loss became severe enough that forest became net neutral in carbon emissions, the rate of growth of CO2 concentrations would increase by 50%.

Forest management and better tilling practices are the most promising ways to induce carbon sequestration. But how much hope is there of that we are not even fully supporting ending tropical deforestation or thinning our own fire-prone western forests?

Many scientists had hoped that serious forest damage would not set in before the middle of the 21st century, and that people would have time to get emissions of heat-trapping gases under control before then. Some of them have been shocked in recent years by what they are seeing.
“The amount of area burning now in Siberia is just startling — individual years with 30 million acres burned,” Dr. Swetnam said, describing an area the size of Pennsylvania. “The big fires that are occurring in the American Southwest are extraordinary in terms of their severity, on time scales of thousands of years. If we were to continue at this rate through the century, you’re looking at the loss of at least half the forest landscape of the Southwest.”