In short, global warming encourages plant growth. Shrubs are currently becoming more abundant, especially on the tundra. These shrubs include dwarf birch and willow. This can be seen in satellite images. This changes the ground's thermal regime. In particular, it increases snow accumulation on the ground and causes permafrost degradation.
This also has many implications for indigenous people. For example, in some parts of Nunavik, caribou used to be hunted. Now, moose are found in these parts. In other places, people cultivated the land so they could pick berries. They can't now, because the shrubs are taking up all the space and smothering the berries. This major change, related to climate change, has side effects.