 The boreal biome is shifting northwards due to climate change, but this shift is not uniform. In particular, the core of the biome has experienced an increase in tree cover, while the periphery has seen a decrease. This suggests that the biome is contracting, leading to potential long-term carbon declines. This article was authored by Ronny Rottbaugh, Egbert H. van Nees, Martin Scheffer, and others.