In the western part of the US, pine bark beetles have thrived, partly because of changing temperatures.

BBC: Why are the world's older trees disappearing?

Bark beetles are known to attack trees already weakened by other environmental factors.

CNN: Global warming threatens forests, study says

The beetles swarm up trees in large numbers, killing them by boring through the bark, sapping their nutrients and emitting a damaging blue fungus.

ECONOMIST: Pining for a cold winter