>book by Ben Rawlence called The Treeline that talks about climate change and the Arctic Treeline

It was from him, I trust the source as he's quite dedicated to the topic of climate change and environmental preservation

But there's no widely acceptable study for this other than Ben Rawlence

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And all the facts on The Arctic heating up and the effects of climate change in the are a seems to match up with the claim.

Yes it is by 40-50m a year, It used to be growing very slowly at a few centimetres a year and now it's receding drastically

There's a good book by Ben Rawlence called The Treeline that talks about climate change and the Arctic Treeline