Once reducers of CO2, Canada's trees now contribute to global warming

In an alarming, yet little noticed series of recent studies, scientists have determined that Canada’s 1.2 million square miles of forests have become so stressed from damage caused by global warming, insect infestations and persistent fires that they have crossed an ominous line and now pump out more carbon dioxide than they take in. The trees make up more than 7 percent of Earth’s total forest lands and have been dubbed the "lungs of the planet" because they could always be depended upon to suck in vast quantities of carbon dioxide, naturally cleansing the world of some of the harmful heat-trapping gas.