Ravenous populations of mountain pine beetles in Canada’s forests are contributing significantly to climate change through killing off large numbers of trees, according to a study in the journal Nature. So far, the beetles have killed trees in over 50,000 square miles of forests in western Canada, and hundreds of thousands of square miles in the western United States. “When trees are killed, they no longer are able to take carbon from the atmosphere. Then when dead trees start to decompose, that releases carbon dioxide into the atmosphere,” said study coauthor Werner Kurz. The study estimates that by 2020, beetle-killed trees in Canada could release some 270 megatons of carbon dioxide into the atmosphere. “This is the kind of feedback we’re all very worried about in the carbon cycle — a warming planet leading to, in this case, an insect outbreak that increases carbon dioxide into the atmosphere, which can increase warming,” said Andy Jacobson of the National Oceanic and Atmospheric Administration.