Quantifying the relative importance of climate-forced and land-use forced land cover changes in the representative concentration pathways

Climate change is projected to cause substantial changes in vegetation distribution, but these changes have been given little attention in comparison to anthropogenic land-use change in the Representative Concentration Pathway (RCP) scenarios. Here we compare climate-forced vegetation changes to anthropogenic changes in vegetation from land-use change. To do this, we use an ensemble of simulations with and without anthropogenic land-use change in Earth System Model HadGEM2-ES for RCP2.6, RCP4.5 and RCP8.5. Climate change causes an expansion poleward of vegetation types. This climate-forced land cover change (LCC) affects more area of land than land-use forced land cover change (often referred to as Land-Use forced Land Cover Change, or LULCC) in all of the RCPs considered here. For forest specifically, the climate-forced forest increase compensates 90% of the global anthropogenic deforestation by 2100 in RCP8.5, but just 3% in RCP2.6. The strong relationship between climate-forced LCC and the overall radiative forcing means that the net effect on forest is strongly dependent on the RCP. Carbon emissions from climate-forced LCC are larger than for LULCC. Overall, bigger LCC contributions tend to originate from LULCC in the shorter term or lower radiative forcing scenarios, and from climate changes in the longer term and higher radiative forcing scenarios. The extent to which climate-forced LCC could mitigate LULCC raises difficult questions regarding global forest and biodiversity offsetting, especially at different timescales. This research shows the importance of considering the relative size of climate-forced LCC to LULCC, especially with regard to the net ecological effects of the different RCPs.