Land Use Change from Zero Agricultural Productivity Growth

luc_scenariosFuture land cover will have a significant impact on climate and is strongly influenced by the extent of agricultural land-use. Differing assumptions of crop yield increase and carbon pricing mitigation strategies affect projected expansion of agricultural land in future scenarios. In the CMIP5 Representative Concentration Pathway RCP4.5, the biogeochemical (greenhouse gas emissions etc.) effects of these land cover changes are included, though the biogeophysical effects (albedo, surface roughness and latent heat transfer, etc.) are not. The afforestation in RCP4.5 has important biogeophysical impacts on climate, in addition to the land carbon changes, which are directly related to the assumption of crop yield increase and the universal carbon tax.

To investigate the biogeophysical climatic impact of combinations of agricultural crop yield increases and carbon pricing mitigation, five scenarios of land-use change based on RCP4.5 are used as inputs to an earth system model (HadGEM2-ES). Simulations are run with combinations of no land use change; standard RCP 4.5 land use change; business as usual land use change; and zero agricultural productivity growth (see figure above for a representation of the different simulations) . The model simulations use the set biogeochemical climate forcing of the RCP 4.5 scenario, but the biogeophysical land use change specification is altered over a 95 year simulation (2005 – 2100).

In the scenario with the greatest increase in agricultural land (due to no increase in crop yield and no climate mitigation) there is a significant -0.49 K worldwide cooling by 2100 compared to a control scenario with no land-use change. Regional cooling is up to -2.2 K annually in NE Asia. Including carbon feedbacks from the land-use change gives a small global cooling of -0.067 K.

This work shows that there are significant impacts from biogeophysical land-use changes caused by assumptions of crop yield and carbon mitigation, which mean that land carbon is not the whole story. It also elucidates the potential conflict between cooling from biogeophysical climate effects of land-use change and wider environmental aims.

The full paper is now available in Journal of Climate: Climatic impacts of land-use change due to crop yield increases and a universal carbon tax from a scenario model. The author’s post-print version can be download here. (Note, this is actually the version that appears in my thesis, but it is functionally the same as the paper.)

This research was picked up by carbonbrief in their daily climate and energy new climate research links.