Biogeophysical impacts of land use change on climate extremes in low emission scenarios: Results from HAPPI-Land

The impacts of land use have been shown to have considerable influence on regional climate. With the recent international commitment to limit global warming to well below 2˚C, emission reductions need to be ambitious and could involve major land-use change (LUC). Land-based mitigation efforts to curb emissions growth include increasing terrestrial carbon sequestration through reforestation, or the adoption of bioenergy crops. These activities influence local climate through biogeophysical feedbacks however it is uncertain how important they are for a 1.5 degree climate target. This was the motivation for HAPPI-Land: the Half a degree Additional warming, Prognosis and Projected Impacts – Land use scenario experiment. Using four Earth System Models we present the first multi-model results from HAPPI-Land and demonstrate the critical role of land use for understanding characteristics of regional climate extremes in low-emission scenarios. In particular, our results show that changes in temperature extremes due to LUC are comparable in magnitude to changes arising from half a degree of global warming. We also demonstrate that LUC contributes to more than 20% of the change in temperature extremes for large land areas concentrated over the Northern Hemisphere. However, we also identify sources of uncertainty that influence the multi-model consensus of our results including how LUC is implemented and the corresponding biogeophysical feedbacks that perturb climate. Therefore our results highlight the urgent need to resolve the challenges in implementing LUC across models to fully understand what the biogeophysical effects are and consider how land use contributes to regional changes in extremes associated with sustainable development pathways.