Attributing temperature trends across altitudes using a surface energy balance approach

Understanding why temperature trends differ across altitudes remains challenging, particularly in mountainous regions where local feedbacks and limited long-term observations make attribution difficult. Here, we analyze long-term (1940–2025) time series of surface energy balance components from ERA5 reanalysis to identify trends in surface temperature and to attribute these to trends in radiative fluxes. We then assess the robustness of these relationships using observations from Baseline Surface Radiation Network (BSRN) stations spanning different altitudes. Our results show a consistent increase in surface temperature across altitudes. While trends in absorbed solar radiation exhibit significant variability, downwelling longwave radiation increases systematically. This confirms its key role in driving surface warming. We then apply a framework that decomposes longwave radiation using the semi-empirical formulation of Brutsaert (1975), combined with thermodynamic constraints from the maximum power principle applied to the surface energy balance. This enables us to investigate the conditions under which enhanced climate sensitivity at higher altitudes may arise. This approach links observed trends in reanalysis data to a thermodynamically constrained surface energy balance, providing a basis for diagnosing the role of atmospheric emissivity and moisture changes in shaping temperature trends at different altitudes. Future work will extend this framework to higher spatial resolutions to better capture the sensitivity of surface temperature to atmospheric emissivity across complex terrain and at different altitudinal settings.