The biogeophysical effects of idealized land cover and land management changes in Earth System Models

Abstract

Abstract. Land cover and land management change (LCLMC) has been highlighted for its critical role in mitigation scenarios, both in terms of global mitigation and local adaptation. Yet, the climate effect of individual LCLMC options, their dependence on the background climate and the local vs. non-local responses are still poorly understood across different Earth System Models (ESMs). Here we simulate the climatic effects of LCLMC using three state-of-the-art ESMs, including the Community Earth System Model (CESM), the Max Planck Institute for Meteorology Earth System Model (MPI-ESM) and the European Consortium Earth System Model (EC-EARTH). We assess the LCLMC effects using four idealized experiments: (i) a fully afforested world, (ii) a world fully covered by cropland, (ii) a fully afforested world with extensive wood harvesting, and (iv) a full cropland world with extensive irrigation. In these idealized sensitivity experiments, performed under present-day climate conditions, the effects of the different LCLMC strategies represent an upper bound for the potential of global mitigation and local adaptation. To disentangle the local and non-local effects from the LCLMC, a checkerboard-like LCLMC perturbation, i.e., alternating grid boxes with and without LCLMC, is applied. The local effects of deforestation on surface temperature are largely consistent across the ESMs and the observations, with a cooling in boreal latitudes and a warming in the tropics. However, the energy balance components driving the change in surface temperature show less consistency across the ESMs and the observations. Additionally, some biases exist in specific ESMs, such as a strong albedo response in CESM mid-latitudes and a soil thawing driven warming in boreal latitudes in EC-EARTH. The non-local effects on surface temperature are broadly consistent across ESMs for afforestation, though larger model uncertainty exists for cropland expansion. Irrigation clearly induces a cooling effect, however; the ESMs disagree whether these are mainly local or non-local effects. Wood harvesting is found to have no discernible biogeophysical effects on climate. Our results overall underline the potential of ensemble simulations to inform decision making regarding future climate consequences of land-based mitigation and adaptation strategies.

TIMBER v0.1: a conceptual framework for emulating temperature responses to tree cover change

“…For example, in the latitudinal band 40°N to 65°N, EC-EARTH based predictions show a cooling trend after +25% tree cover change, in contrast to the warming trend seen in other ESMs. Such a difference was also noted in(De Hertog et al, 2022) and attributed to lower amounts of boreal afforestation implemented. Over all latitudinal bands and months shown, largest 95% intervals occur towards the extreme ends of tree cover change for both observations and ESM based predictions.…”

“…response patterns across all tree cover changes (Figure 6), inter-ESM differences become quite apparent. Such differences are continuously studied and mainly arise from differences in model physical representation (Boisier et al, 2012;Lawrence et al, 2016;Lejeune et al, 2018;Davin et al, 2020;Boysen et al, 2020;De Hertog et al, 2022).…”