It's kind of an obvious implication to there being more CO2 in the atmosphere. Plants like it. If it gets warmer at higher latitudes, there will also be more plants able to grow there.
There was a 200 page report on global warming from the 1980s on HN a few days ago which had several sections on this as upsides to global warming. I only read 50 pages of it, but it is a remarkably clear and level headed document.
One serious caveat about the "plants like more CO2" idea:
The increase in CO2 strongly disfavors slow-growing old groth and established ecosystems, and favors fast growing plants, which are typically invasive species that take over and destroy established ecosystems, and reduce biodiversity.
There was a 200 page report on global warming from the 1980s on HN a few days ago which had several sections on this as upsides to global warming. I only read 50 pages of it, but it is a remarkably clear and level headed document.
https://news.ycombinator.com/item?id=19251316