Global effects of different types of land use and land cover changes on near-surface air temperature

Understanding the climate effect of land use and land cover change (LULCC) is critical for guiding human ac-tivities towards environmental sustainability. Previous studies have reported the climate effects of global deforestation, vegetation greening and crop cultivation changes. However, the contribution of each type of land state, land transition and land management to LULCC's climate effects remain underexamined. In this study, we estimated global biophysical temperature effects of LULCC using CMIP6 climate models, with special attention on the relative contribution (RC) of 12 land state changes, 113 land transitions and 10 land managements. The results show a large difference in the simulated LULCC's temperature effect between CESM2 and UKESM1-0-LL, and the two models even disagree in the sign of LULCC's effects in most of northern hemisphere except for autumn. Based on the weighted mean of two models, we found that historical LULCC has exerted a global warming effect at a rate of 0.0025 degrees C/century, with the largest warming effect in autumn. Spatially, a significant (p < 0.05) cooling effect is found from 60 degrees N to 40 degrees N, while the warming trend dominates the areas from 40 degrees N to 30 degrees S. Based on regression modelling, historical changes in forested/non-forested secondary land, urban land and cropland have contributed over 70% to LULCC's temperature effect, with land transitions from secondary land to cropland and from cropland to urban land dominating the climate effect at global scale. For land management, the climate effect of irrigation is larger than that of nitrogen fertilizer application. Furthermore, the application of nitrogen fertilizer for C3 plant has larger impacts compared to C4 plants, while similar effects of irrigation are observed for different types of croplands. Besides, the large difference in temperature effect between CESM2 and UKESM1-0-LL may be the difference in the forestland and cropland changes. Our study calls for explicit ex-amination of the climate effect induced by different types of land state-change, land transition and land man-agement for developing targeted land use policies in the future.