A widely publicized study published last year by researchers at the University of Northern Arizona analyzed satellite images taken between 1985 and 2019. They show that large parts of the boreal forest have “browned” (i.e., died) in the south and greened with trees and shrubs in the north. If this shift, long hypothesized as a future outcome of warming, is already underway, the effects will be profound, transforming natural habitats, animal migration and human settlements.