ALBERT

Description: The energy budgets over land and oceans are still afflicted with considerable uncertainties, despite their key importance for terrestrial and maritime climates. We evaluate these budgets as represented in 43 CMIP5 climate models with direct observations from both surface and space and identify substantial biases, particularly in the surface fluxes of downward solar and thermal radiation. These flux biases in the various models are then linearly related to their respective land and ocean means to infer best estimates for present day downward solar and thermal radiation over land and oceans. Over land, where most direct observations are available to constrain the surface fluxes, we obtain 184 and 306 Wm-2 for solar and thermal downward radiation, respectively. Over oceans, with weaker observational constraints, corresponding estimates are around 185 and 356 Wm-2. Considering additionally surface albedo and emissivity, we infer a surface absorbed solar and net thermal radiation of 136 and -66 Wm-2 over land, and 170 and -53 Wm-2 over oceans, respectively. The surface net radiation is thus estimated at 70 Wm-2 over land and 117 Wm-2 over oceans, which may impose additional constraints on the poorly known sensible/latent heat flux magnitudes, estimated here near 32/38 Wm-2 over land, and 16/100 Wm-2 over oceans. Estimated uncertainties are on the order of 10 and 5 Wm-2 for most surface and TOA fluxes, respectively. By combining these surface budgets with satellite-determined TOA budgets we quantify the atmospheric energy budgets as residuals (including ocean to land transports), and revisit the global mean energy balance. This study has recently been published online in Climate Dynamics.

Description: The genesis and evolution of Earth’s climate is largely regulated by the global energy balance. Despite the central importance of the global energy balance for the climate system and climate change, substantial uncertainties still exist in the quantification of its different components, and its representation in climate models. While the net radiative energy flow in and out of the climate system at the top of atmosphere is known with considerable accuracy from new satellite programs such as CERES, much less is known about the energy distribution within the climate system and at the Earth surface. Accordingly, the quantification of the global energy balance has been controversially disputed in the past. Here we review this discussion and make an attempt to put additional constraints on the components with largest uncertainties. In addition to satellite observations, we thereby make extensive use of the growing number of surface observations to constrain the global energy balance not only from space, but also from the surface. We combine these observations with the latest modeling efforts performed for the 5th IPCC assessment report (CMIP5) to infer best estimates for the global mean surface radiative components. Our analyses favor global mean downward surface solar and thermal radiation values near 185 and 342 Wm-2, respectively, which are most compatible with surface observations. These estimates are lower and higher, respectively, than in many previous assessments, including those presented in previous IPCC reports. It is encouraging that our estimates, which make full use of the information contained in the surface networks, coincide within 2 Wm-2 with the latest satellite-derived estimates (Stephens et al. 2012, Kato et al. submitted to J. Climate), which are completely independently determined. Combining our above estimates with an estimated global mean surface absorbed solar radiation and thermal emission of 161 Wm-2 and 397 Wm-2, respectively, results in 106 Wm-2 of surface net radiation globally available for distribution amongst the non-radiative surface energy balance components. The 23 CMIP5 models investigated in this study overestimate the downward solar and underestimate the downward thermal radiation, both by 5-10 Wm-2 on average. Thus, the CMIP5 models nevertheless simulate an adequate global mean surface net radiation, by error compensation in their downward solar and thermal components. This also suggests that, globally, the simulated surface sensible and latent heat fluxes, around 20 and 85 Wm-2 on average, state realistic values. The findings of this study are compiled into a new global energy balance diagram, and may be able to reconcile currently disputed inconsistencies between global mean energy and water cycle estimates. The study is published online in Climate Dynamics. Wild, M., Folini, D., Schär, C., Loeb, N., Dutton, E.G., and König-Langlo, G., 2013: The global energy balance from a surface perspective, Clim. Dyn., published online. Doi:10.1007/s00382-012-1569-8.

Description: The energy budgets over land and oceans are key determinants of terrestrial and maritime climates. Traditionally, however, large uncertainties have been inherent in the estimates of these budgets, which is still reflected in largely differing energy budgets in the latest generation of global climate models (CMIP5). We combine a comprehensive set of radiation observations with 43 state-of-the-art global climate models from CMIP5 to infer best estimates for downward solar and thermal radiation averaged over land and ocean surfaces. Over land, where most direct observations are available to constrain the surface fluxes, we obtain 185 and 305 Wm-2 for the solar and thermal downward radiation, respectively. Over oceans, with weaker observational constraints, our best estimates are around 186 and 356 Wm-2 for the solar and thermal downward radiation. These values closely agree, mostly within 3 Wm-2, with the respective quantities independently derived by recent state-of-the-art reanalyses (ERA-Interim) and satellite-derived products (surface CERES EBAF). This remarkable consistency enhances confidence in the determined flux magnitudes, which so far caused large uncertainties in the energy budgets and often hampered an accurate simulation of surface climates in models. Considering additionally surface albedo and emission, we infer an absorbed solar and net thermal radiation over land of 138 and -67 Wm-2, and over ocean of 170 and -53 Wm-2, respectively. Best estimates for the surface net radiation thus amount to 71 Wm-2 over land and 117 Wm-2 over oceans, which may provide better constraints for the respective sensible and latent heat fluxes. Combining these surface budgets with satellite-determined TOA budgets (CERES-EBAF) results in an atmospheric solar absorption of 75 and 82 Wm-2 and a net atmospheric thermal emission of -165 and -190 Wm-2 over land and oceans, respectively.

Description: The genesis and evolution of Earth’s climate is largely regulated by the Earth radiation balance. Despite of its key role in the context of climate change, substantial uncertainties still exist in the quantification of the magnitudes of its different components, and its representation in climate models. While the net radiative energy flows in and out of the climate system at the top of atmosphere are now known with considerable accuracy from new satellite programs such as CERES and SORCE, the energy distribution within the climate system and at the Earth’s surface is less well determined. Accordingly, the magnitudes of the components of the surface energy balance have recently been controversially disputed, and potential inconsistencies between the estimated magnitudes of the global energy and water cycle have been emphasized. Here we summarize this discussion as presented in Chapter 2.3 of the 5th IPCC assessment report (AR5). In this context we made an attempt to better constrain the magnitudes of the surface radiative components with largest uncertainties. In addition to satellite observations, we thereby made extensive use of the growing number of surface observations to constrain the radiation balance not only from space, but also from the surface. We combined these observations with the latest modeling efforts performed for AR5 (CMIP5) to infer best estimates for the global mean surface radiative components. Our analyses favor global mean values of downward surface solar and thermal radiation near 185 and 342 Wm-2, respectively, which are most compatible with surface observations (Wild et al. 2013). These estimates are on the order of 10 Wm-2 lower and higher, respectively, than in some of the previous global energy balance assessments, including those presented in previous IPCC reports. It is encouraging that these estimates, which make full use of the information contained in the surface networks, coincide within 2 Wm-2 with the latest satellite-derived estimates (Kato et al. 2013), which are completely independently determined. This enhances confidence in these recent surface flux estimates. IPCC AR5 further presents increasing evidence from direct observations that the surface radiative fluxes undergo significant changes on decadal timescales, not only in their thermal components as expected from the increasing greenhouse effect, but also in the amount of solar radiation that reaches the Earth surface. In the thermal range, surface observations suggest an overall increase of downward thermal radiation in line with latest projections from the CMIP5 models and expectations from an increasing greenhouse effect. On the other hand the strong decadal changes in surface solar radiation seen in the observations (“dimming/brightening“) are not fully captured by current climate models. These decadal changes in surface solar radiation may largely affect various aspects of climate change.

Description: The energy budget over terrestrial surfaces is a key determinant of the land surface climate and governs a variety of physical, chemical and biological surface processes. The purpose of the present study is to establish new reference estimates for the different components of the energy balance over global land surfaces. Thanks to the impressive progress in space-based observation systems in the past decade, we now know the energy exchanges between our planet and the surrounding space with unprecedented accuracy. However, the energy flows at the Earth’s surface have not been established with the same accuracy, since they cannot be directly measured from satellites. Accordingly, estimates on the magnitude of the fluxes at terrestrial surfaces largely vary, and latest climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) still show significant differences in their simulated energy budgets on a land mean basis, which prevents a consistent simulation of the land surface processes in these models. In the present study we use to the extent possible direct observations of surface radiative fluxes from the Global Energy Balance Archive (GEBA) and the Baseline Surface Radiation Network (BSRN) to better constrain the simulated fluxes over global land surfaces. These model-calculated fluxes stem from the comprehensive set of more than 40 global climate from CMIP5 used in the latest IPCC report AR5. The CMIP5 models overall still show a tendency to overestimate the downward solar and underestimate the downward thermal radiation at terrestrial surfaces, a long standing problem in climate modelling. Based on the direct radiation observations and the bias structure of the CMIP5 models we infer best estimates for the downward solar and thermal radiation averaged over global land surfaces. They amount to 184 Wm-2 and 306 Wm-2, respectively. These values closely agree with the respective quantities independently derived by recent state-of-the-art reanalyses (ERA-Interim) and satellite-derived products (surface CERES EBAF). This remarkable consistency enhances confidence in the determined flux magnitudes, which so far caused large uncertainties in the energy budgets and often hampered an accurate simulation of surface climates in models. Using in addition a land mean surface albedo estimate of 0.26, we determine an average absorbed solar radiation at land surfaces of 136 Wm-2. Our best estimate for the upward thermal radiation at land surfaces (essentially based on the Stefan Boltzmann law) is 372 Wm-2, and combined with the above best estimate of 306 Wm-2 for the downward thermal radiation, this results in a net thermal radiation of -66 Wm-2 averaged over global land surfaces. Adding the absorbed solar and net thermal radiation, our best estimate of the land mean surface net radiation amounts to 70 Wm-2, which is the energy available for the sensible and latent heat fluxes. Latest estimates of terrestrial latent heat fluxes indicate a land mean value slightly below 40 Wm-2. In our best estimate of the global land mean energy balance we thus adopt a land mean latent heat flux of 38 Wm-2, leaving a land mean sensible heat flux of 32 Wm-2 as residual to close the energy balance over terrestrial surfaces. A diagram of the global land mean energy balance including these new estimates and the related discussion has recently been published in Climate Dynamics (Wild et al. 2015).