SummaryThe CO2transfer conductance within plant leaves (mesophyll conductance,gm) is currently not considered explicitly in most land surface models (LSMs), but instead treated implicitly as an intrinsic property of the photosynthetic machinery. Here, we review approaches to overcome this model deficiency by explicitly accounting forgm, which comprises the re‐adjustment of photosynthetic parameters and a model describing the variation ofgmin dependence of environmental conditions. An explicit representation ofgmcauses changes in the response of photosynthesis to environmental factors, foremost leaf temperature, and ambient CO2concentration, which are most pronounced whengmis small. These changes in leaf‐level photosynthesis translate into a stronger climate and CO2response of gross primary productivity (GPP) and transpiration at the global scale. The results from two independent studies show consistent latitudinal patterns of these effects with biggest differences in GPP in the boreal zone (up to ~15%). Transpiration and evapotranspiration show spatially similar, but attenuated, changes compared with GPP. These changes are indirect effects ofgmcaused by the assumed strong coupling between stomatal conductance and photosynthesis in current LSMs. Key uncertainties in these simulations are the variation ofgmwith light and the robustness of its temperature response across plant types and growth conditions. Future research activities focusing on the response ofgmto environmental factors and its relation to other plant traits have the potential to improve the representation of photosynthesis in LSMs and to better understand its present and future role in the Earth system.