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.

Changes in Land Cover and Management Affect Heat Stress and Labor Capacity

“…There are several limitations and caveats to this analysis. The main methodological challenges and limitations to the implementation of the conducted sensitivity experiments are well described in (De Hertog et al, 2023).…”

“…The differences in climate responses between CROP and CTL simulations (CROP-CTL) show the effects of cropland expansion; IRR-CROP shows the effects of irrigation expansion in a cropland world; and FRST-CTL quantifies the climate response to full afforestation starting from present-day conditions. In EC-Earth, irrigation does not induce any local effects on climate because irrigation implemented in the process-based vegetation model, LPJ-GUESS, does not affect moisture fluxes in the atmosphere due to disconnected water cycles of the land surface model interface to the atmospheric boundary layer (De Hertog et al, 2023). Therefore, for the sensitivity experiment of irrigation expansion, we only discuss results of CESM and MPI-ESM simulations.…”

“…Below, we provide a short description of the conducted sensitivity experiments on LCLMC. A detailed description of the model simulations can be found in (De Hertog et al, 2023).…”

“…In CESM, the local effects of cropland expansion result in an increase of annual average near-surface air temperature (hereafter: temperature) in the tropics due to decreased evapotranspiration rates, whereas the boreal regions experience an albedo-induced cooling (De Hertog et al, 2023) (Figure S2 in Supporting Information S1). For low latitudes, the absolute increase of ESI is less pronounced than the temperature increase, because of a reduction in (relative and specific) humidity.…”

“…Specifically, we investigate the effectiveness of LCLMC as adaptation strategies for reducing heat stress. Our global analysis builds upon the results from stylized global sensitivity experiments for three LCLMC practices (a) cropland expansion, (b) irrigation expansion, and (c) afforestation, which are described and analyzed in (De Hertog et al, 2023). To directly separate between local and non-local effects of LCLMC, the checkerboard approach developed by Winckler et al (2017a) was applied in these simulations.…”