Abstract

Radiative energy flux data, downloaded from CERES, are evaluated with respect to their variations from 2001 to 2020. We found the declining outgoing shortwave radiation to be the most important contributor for a positive TOA (top of the atmosphere) net flux of 0.8 W/m2 in this time frame. We compare clear sky with cloudy areas and find that changes in the cloud structure should be the root cause for the shortwave trend. The radiative flux data are compared with ocean heat content data and analyzed in the context of a longer-term climate system enthalpy estimation going back to the year 1750. We also report differences in the trends for the Northern and Southern hemisphere. The radiative data indicate more variability in the North and higher stability in the South. The drop of cloudiness around the millennium by about 1.5% has certainly fostered the positive net radiative flux. The declining TOA SW (out) is the major heating cause (+1.42 W/m2 from 2001 to 2020). It is almost compensated by the growing chilling TOA LW (out) (−1.1 W/m2). This leads together with a reduced incoming solar of −0.17 W/m2 to a small growth of imbalance of 0.15 W/m2. We further present surface flux data which support the strong influence of the cloud cover on the radiative budget.

Highlights

  • The radiative flux data are compared with ocean heat content data and analyzed in the context of a longer-term climate system enthalpy estimation going back to the year 1750

  • We report radiative flux data and trends in cloudy and cloud-free regions, obtained from CERES and other sources and relate them to the top of atmosphere (TOA) and surface radiative budgets and climate system enthalpy

  • If we define surface albedo as the ratio of the TOA outgoing SW and the incoming solar fluxes, we find a reduction from 15.80% to 15.56% (−0.23% absolute) in the “Clear

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Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Loeb et al [14] found a good agreement between radiative (CERES) and OHC data for the period mid-2005 to mid-2019 These authors have further studied the influencing factors for the shortwave (SW) and longwave (LW) radiative fluxes and concluded that cloud changes have fostered the downwelling shortwave radiation. Loeb et al reported a decreasing TOA SW trend, mainly caused by a reduction in low cloud cover, and Ollila concluded that this increasing downwelling SW, which is strong since 2014, may be responsible for a new wave of heating after the hiatus This finding is in conflict with the assumption that further global warming originates mainly from the LW radiation capture caused by greenhouse gases, i.e., a decline of outgoing LW. We discuss these results in a longer-term context and suggest a possible correlation of cloud cover shifts such as the one around the millennium with the AMO (Atlantic Multidecadal Oscillation)

Datasets and Evaluation
Results and Discussion
K higher in the Southern compared with the
Net fluxover
10. Global averageaverage
11. Global average
Effect on the Climate System’s Enthalpy
Conclusions

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