WISE RIVER, MONTANA, USA, October 1, 2011 (The NY Times): 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.
Scientists have figured out — with the precise numbers deduced only recently — that the world’s forests have been absorbing more than a quarter of the carbon dioxide that people are putting into the air by burning fossil fuels and other activities. It is an amount so large that trees are effectively absorbing the emissions from all the world’s cars and trucks.
If forests were to die on a sufficient scale, they would not only stop absorbing carbon dioxide, they might also start to burn up or decay at such a rate that they would spew huge amounts of the gas back into the air — as is already happening in some regions. That, in turn, could speed the warming of the planet, unlocking yet more carbon stored in once-cold places like the Arctic.
Scientists are not sure how likely this feedback loop is, and they are not eager to find out the hard way.
“It would be a very different world than the world we’re in,” said Christopher B. Field, an ecologist at the Carnegie Institution for Science.
Forest 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.
“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.
Insects empowered by the new normal in climate are part of the issue. Pine beetles are a natural part of the life cycle in Western forests, but the most recent outbreak, under way for more than a decade in some areas, is by far the most extensive ever recorded. As the climate has warmed, various beetle species have marauded across the landscape, from Arizona to Alaska. The situation is worst in British Columbia, which has lost millions of trees across an area the size of Wisconsin.Scientists say winter temperatures used to fall to 40 degrees below zero in the mountains every few years, killing off many beetles. “It just doesn’t happen anymore,” said a leading climate scientist from the University of Montana, Steven W. Running, who was surveying the scene with Dr. Six one recent day.
The oceans are taking up about a quarter of the carbon emissions arising from human activities. That is causing the sea to become more acidic and is expected to damage marine life over the long run, perhaps catastrophically.
Trees are taking up a similar amount of carbon, but whether this will continue is much less certain, as the recent forest damage illustrates.