In itself it just is what it is, and in the abstract entirely to be expected. But it has implications for humans. Trees replacing tundra causes more sunlight t

In itself it just is what it is, and in the abstract entirely to be expected. But it has implications for humans. Trees replacing tundra causes more sunlight to be absorbed when the sun is at low angles in the sky (spring and fall). The trees themselves are darker than the sedges and herbs they replace, which further increases sunlight absorption throughout the light part of the year. This increases air temperature and so increases the amount of water vapor that the air can hold, which increases the intensity of storms when they happen, possibly thousands of miles away. Locally, the heating might destabilize permafrost more rapidly than previously modelled, as one further effect. The implications of that would also have bad effects on humans and their structures. On the positive side, models of forest colonization processes might be improved. As a general note, this pattern of climate and cryosphere scientists saying "that's not supposed to happen yet!" has been a constant theme of the last 20 years.