Abstract
The warming climate significantly modifies the global water cycle. Global evapotranspiration has increased over the past decades, yet climate models agree on the drying trend of land surface. In this study, we conducted an intercomparison analysis of the surface energy partitioning across Coupled Model Intercomparison Phase 5 (CMIP5) simulations and evaluated its behaviour with surface temperature and soil moisture anomalies, against the theoretically derived thermodynamic formula. Different responses over land and sea surfaces to elevated greenhouse gas emissions were found. Under the Representative Concentration Pathway of +8.5 W m−2 (RCP8.5) warming scenario, the multi-model mean relative efficiency anomaly from CMIP5 simulations is 3.83 and −0.12 over global sea and land, respectively. The significant anomaly over sea was captured by the thermodynamic solution based on the principle of maximum entropy production, with a mean relative error of 14.6%. The declining trend over land was also reproduced, but an accurate prediction of its small anomaly will require the inclusions of complex physical processes in future work. Despite increased potential evapotranspiration under rising temperatures, both CMIP5 simulations and thermodynamic principles suggest that the soil moisture-temperature feedback cannot support long-term enhanced evapotranspiration at the global scale. The dissipation of radiative forcing eventually shifts towards sensible heat flux and accelerates the warming over land, especially over South America and Europe.
Highlights
During the 20th century, intensification of the global hydrological cycle has been observed [1], and the trend is expected to continue under a warming climate [2]
The question remains: how large is the variety in surface energy partitioning across Coupled Model Intercomparison Phase 5 (CMIP5) simulations, given the different parameterizations and feedbacks in global climate models? To address this question, we examined results from historical, RCP4.5 (Representative Concentration Pathway of +4.5 W m−2 )
Climate models consistently show that the global land surface warms faster than the sea surface, and the gap in surface temperature anomaly between land and sea rapidly expands with increased atmospheric greenhouse gas concentration in the future
Summary
During the 20th century, intensification of the global hydrological cycle has been observed [1], and the trend is expected to continue under a warming climate [2]. While trends of individual climatic indicators (temperature, humidity, energy budgets, etc.) tend to ramify, we believe that there exist some intrinsic measures/constraints of climate changes. These measures should preferably be derived from the thermodynamic principles and be capable of providing a more fundamental explanation of the behaviors in anomalies of the coupled energy and water cycles among different General Circulation Models (GCMs), with a limited number of parameters and reduced uncertainty. The question remains: how large is the variety in surface energy partitioning across CMIP5 simulations, given the different parameterizations and feedbacks in global climate models? RCP8.5 scenarios in CMIP5 simulations against a theoretically derived relationship
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