Yale Environment 360: Milder winters can't be blamed for the full extent of recent mountain pine beetle outbreaks in the western United States, according to a new study by Dartmouth and U.S. Forest Service researchers. Winters have been warming across the western U.S. states for decades, as overall the coldest winter night has warmed by 4 degrees C since 1960. But that warming trend could only be the primary driver of increasing pine beetle outbreaks in regions where winter temperatures have historically killed most of...