This paper started off with a simple question: is the amount of land use change a good guide to how much net climate effect it will have? But it came up with a different sort of answer: that afforestation is not the panacea that we might hope it would be, and may even be a perverse incentive when it comes to climate.
You might expect that the amount of land use change would be a good guide as to how much it affect the climate, i.e. more land use change, more change to climate, less land use change, less change to climate. But this isn’t the case. The carbon emissions are approximately proportional to the land use change, but there are other factors – changes to the surface reflectance (albedo) and the evapotranspiration – that are not so linear. The result of these other effects are that in one of the IPCC projection of future climate change, the afforestation policy implimented to help mitigate climate actually causes warming rather than cooling. The warming isn’t very much, only about 0.1 K in 2070 to 2100, but it is enough that the afforestation isn’t doing what it was intended to do. However, extending and preserving forest would have a host of other benefits to biodiversity and ecosystem services. Before we chuck out afforestation as an idea all together because it may not benefit the climate, it’s important to think about other things that forest can provide.
If you’re interested in reading more, wander over to the full paper, published in Environmental Research Letters: Full effects of land use change in the representative concentration pathways. (It’s open access, so everyone can read it. Yay!) You can also engage me in discussion on twitter: @tdaviesbarnard