Drought stalls tree growth and shuts down Amazon carbon sink

[NickB79]

8. Even if we could do that, sequestration via reforestation would take millenia to reduce CO2

Natural processes can scrub CO2 at a rate of approximately 1ppm per thousand years.

We're at least 50 ppm above sustainable levels, and rising at 3-4ppm per YEAR at this point. Humanity might honestly be extinct by the time reforestation effectively stops climate change.

And in fact, reforestation to combat global warming has been studied, and the results are not good: https://www.newscientist.com/article/dn20587-planting-forests-wont-stop-global-warming/

To get a fuller picture, Vivek Arora of Environment Canada and the University of Victoria, British Columbia, and Alvaro Montenegro of St Francis Xavier University in Antigonish, Nova Scotia, Canada, used a computer model to estimate the overall effect of reforesting.

They used what they admit are “somewhat extreme” scenarios in which half or all of the world’s croplands have been converted to forests by 2060. Foresting all or half the world’s cropland reduced global temperatures in 2100 by 0.45 °C and 0.25 °C respectively.

Arora reckons that no more than 10 to 15 per cent of existing cropland is likely to be forested, so the effects will be even smaller. “The overall temperature benefits of any realistic afforestation efforts are expected to be marginal,” he says.

So, reforesting ALL of the world's cropland would reduce global temps by less than 0.5C by 2100. To put that in perspective, we're already 1C above pre-industrial levels.