From New Mexico to British Columbia, the region's signature pine forests are succumbing to a huge infestation of mountain pine beetles that are turning a blanket of green forest into a blanket of rust red. Montana has lost a million acres of trees to the beetles, and in northern Colorado and southern Wyoming the situation is worse.

Old-growth forests remove carbon dioxide (CO2) from the atmosphere, helping to curb the greenhouse gases that drive global warming, according to a study to be published Thursday. Many environmental policies are based on the assumption that only younger forests, mainly in the tropics, absorb significantly more CO2 than they release. As a result, primary forests in temperate and subarctic regions of the northern hemisphere do not figure in climate change negotiations seeking ways to reward countries that protect carbon-absorbing woodlands within their borders.

Warmer temperatures and longer dry spells have killed thousands of trees and shrubs in a Southern California mountain range, pushing the plants' habitat an average of 213 feet up the mountain over the past 30 years, a UC Irvine study has determined. Almost all of the studied plants crept up the mountain a similar distance, countering the belief that slower-growing trees would move slower than faster-growing grasses and wildflowers.

A beetle about the length of a well-trimmed fingernail may be challenging scientists' projections for global warming. An infestation of mountain pine beetles is turning more than 144,000 square miles of woods in British Columbia from a slight carbon absorber -- or sink -- to a net CO2 emitter. Canadian scientists unveiled projections Wednesday that between 2000 and 2020, the forest will have lost 270 million tons of carbon into the atmosphere.

Scientists have long thought it would take generations if not centuries for tree populations to shift in response to a warming world. But scientists' work on suggests that climate change might affect New England forests far sooner than scientists thought.

Researchers have found that wildfires  fuelled by climate change  may be turning boreal forests into sources of carbon dioxide. The boreal forests in northern Canada, Alaska, Siberia, China, Scandinavia and elsewhere were believed by scientists to as a carbon sink. But new research from the University of Wisconsin-Madison has found that the forests may be emitting more carbon than they are absorbing.

Planting forests to combat global warming may be a waste of time, especially if those trees are at high latitudes. Scientists say the benefits that come from trees reducing atmospheric carbon dioxide can be outweighed by their capacity to trap heat near the ground.

The vast Amazon rainforest is on the brink of being turned into desert, with catastrophic consequences for the world's climate, alarming research suggests. And the process, which would be irreversible, could begin as early as next year.

A new study led by scientists at Scripps Institution of Oceanography at the University of California, San Diego, implicates rising seasonal

temperatures and the earlier arrival of spring conditions in connection with a dramatic increase of large wildfires in the western United States.

Canadian forests are at risk from rising temperatures, according to a government agency, which warns that an increased intensity of fires and insect outbreaks could  ravage the forests, affecting the forestry industry and the communities that are based in the forest.

Planting trees in the Amazon to curb global warming is unlikely to work. Brazilian and US scientists have found the rainforest emits more of the greenhouse gas carbon dioxide than it absorbs when conditions are very wet. Their report, published in the journal Science, comes just three days before the latest United Nations negotiations on climate change take place in Milan. The researchers say previous studies have almost certainly over-estimated how much CO2 the Amazon can take in.

The long-standing debate about the Amazon's role in global climate change is intensifying. The Amazon is the largest tropical forest in the world -- bigger than all of Europe, with Brazil's section alone more than half the size of the continental United States. And it has always been assumed to be essential to inhibiting global warming by drawing in carbon dioxide during photosynthesis.  But it has never been established whether the rain forest here is in fact functioning as a giant sink that "sequesters," or traps and absorbs, carbon.

A new experiment has shown that fairly common concentrations of low-level ozone, the eye-stinging ingredient in smog, can sharply impede the ability of trees to absorb heat-trapping carbon dioxide.

Mature trees might not offset global warming by mopping up excess carbon dioxide, suggests a forest study in Switzerland. They may already have all the carbon dioxide that they need. If the phenomenon is widespread, it could be a setback to those hoping that existing and newly planted forests will buffer mounting CO₂ levels.

It was a comforting dream while it lasted: Carbon dioxide spewed into the air from tailpipes and smokestacks would speed up the growth of forests. The forests in turn would store the carbon in wood and soil, staving off climate change. But the latest research has delivered an unpleasant wake-up call.