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Comment by keiferski | Hacker News Reader

Serious question from a non-climate scientist: would an increase in global temperatures due to climate change ultimately cause more greenery, due to new growth in previously too-cold areas?

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Well, I don't know about temperature, but we do know that plants grow faster in the presence of excessive CO2. But that's a double-edged sword, because their nutritional value per unit mass goes down, in terms of trace nutrients - with abundant CO2, they can use more air to build more empty carbs, but that means the critical nutrients they pull from the soil are present in lower concentrations.

You can easily see this effect on Highways (in Europe where trees are planted just at the edge of the road). The trees there are the first ones that turn green (and get greener much faster) while the trees in the farmland are still without leaves.

I wonder if that’s due to CO2 levels, warmer temperatures (asphault captures a lot of heat) or human selection for “pretty” trees along the highway.

I think that eco-systems do move to higher latitudes when the earth warms. This happened e.g. at the transition from ice ages. However the problem is that if the rate of warming is too high, eco-systems will not be able spread and adapt fast enough, leading to a net loss of bio-mass.

See e.g. page 3 of https://www.pnas.org/content/pnas/115/33/8252.full.pdf on biogeophysical feedback.

I am afraid the warming rate anticipated currently is at least an order of magnitude higher than any climate changes the earth faced before.

There is less surface around the poles, and previously ok-hot areas at the equator are now likely to become too-hot areas, so it's a net loss in this simple model.

A slightly more nuanced discussion upthread here: https://news.ycombinator.com/item?id=19263836

Most climate models take that into account, from what I've heard. It's not enough to mitigate the rising temperatures, though.

Also need to factor in the too-warm, too-dry and on-fire areas.

it's a bit of a double edged sword. warmer springs are definitely a good thing for plants in terms of growth. but in the united states, at least, there is evidence that the positive effect of warmer springs will be offset by drier, hotter summers that are not ideal for growth.

here is a discussion of a neat study in 2016 that showed this effect: https://www.pnas.org/content/113/21/5768

the already warm tropics are expected to get even warmer, which likely isn't great for the forests there.

Yes. But things like permafrost melting could release massive amounts of methane and CO2 to have a net opposite effect at least for the first decades / centuries.

Another question on the same lines - wouldn't the increase in carbon dioxide also contribute to increased greenery? I guess the more pertinent question would be what amount of greenery could have a reasonable chance at halting the adverse effects of human activities?

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