The energy balance over land and oceans: an assessment based on direct observations and CMIP5 climate models

Martin Wild 0 1 3 4 Doris Folini 0 1 3 4 Maria Z. Hakuba 0 1 3 4 Christoph Schr 0 1 3 4 Sonia I. Seneviratne 0 1 3 4 Seiji Kato 0 1 3 4 David Rutan 0 1 3 4 Christof Ammann 0 1 3 4 Eric F. Wood 0 1 3 4 Gert KnigLanglo 0 1 3 4 0 C. Ammann Research Station Agroscope, Climate and Air Pollution Group , Reckenholzstr. 191, 8046 Zurich , Switzerland 1 S. Kato D. Rutan NASA Langley Research Center , 21 Langley Boulevard, Hampton, VA 23681-2199 , USA 2 ) D. Folini M. Z. Hakuba C. Schar S. I. Seneviratne Institute for Atmospheric and Climate Science, ETH Zurich , Universitatsstr. 16, 8092 Zurich , Switzerland 3 G. Konig-Langlo Alfred Wegener Institute , Bussestrasse 24, 27570 Bremerhaven , Germany 4 E. F. Wood Department of Civil and Environmental Engineering, Princeton University , Princeton, NJ 08544 , USA 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 Wm2 for solar and thermal downward radiation, respectively. Over oceans, with weaker observational constraints, corresponding estimates are around 185 and 356 Wm2. Considering additionally surface albedo and emissivity, we infer a surface absorbed solar and net thermal radiation of 136 and 66 Wm2 over land, and 170 and 53 Wm2 over oceans, respectively. The surface net radiation is thus estimated at 70 Wm2 over land and 117 Wm2 over oceans, which may impose additional constraints on the poorly known sensible/latent heat flux magnitudes, estimated here near 32/38 Wm2 over land, and 16/100 Wm2 over oceans. Estimated uncertainties are on the order of 10 and 5 Wm2 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. 1 Introduction The energy balance of the Earth is a fundamental determinant of the climatic conditions on our planet. Thanks to impressive progress in space-based observation systems in the past decade, we now know the exchanges of radiative energy flows between our planet and surrounding space with unprecedented accuracy. This has enabled detailed assessments of the radiation budgets at the top of atmosphere (TOA) in climate models (e.g., Potter and Cess 2004; Trenberth and Fasullo 2010; Wang and Su 2013; Dolinar et al. 2014). However, the distribution of the radiative energy within the climate system has not been established with the same accuracy, since it cannot be directly measured from satellites. Accordingly, estimates on the magnitude of the energy balance components Fig. 1 Schematic diagram of the global (land and ocean) annual mean energy balance of the Earth. Numbers indicate best estimates for the magnitudes of the globally averaged energy balance components together with their uncertainty ranges in parentheses, representing present day climate conditions at the beginning of the twenty-first century. The surface thermal upward flux contains both the surface thermal emission and a small contribution from the reflected part of the downward thermal radiation. Units Wm2. Adapted from Wild et al. (2013a, b) with slight modifications as discussed in Sect. 5 at the surface and within the atmosphere as presented in the literature largely vary even on a global annual mean basis (e.g., Budyko 1956; Hartmann et al. 1986; Ramanathan 1987; Ohmura and Gilgen 1993; Kiehl and Trenberth 1997; Wild et al. 1998; Hatzianastassiou et al. 2005; Trenberth et al. 2009; Stephens et al. 2012; Stevens and Schwartz 2012; Wild et al. 2013a; Trenberth and Fasullo 2012). Also the surface radiation budgets as represented in climate models thus traditionally largely differ (e.g., Wild et al. 1995b, 2013a; Wild 2008; Stephens et al. 2012; Li et al. 2013). Recently, progress has been made to better constrain these budgets not only at the TOA, but also at the surface, taking into account latest modeling efforts and surface observations on the one hand (Wild et al. 2013a) as well as improved satellite retrievals from both passive and active sensors on the other hand (Kato et al. 2013). Here we expand the study of Wild et al. (2013a) to further decompose the global mean energy balance estimates as shown in Fig. 1 into their land and ocean domains. This is illustrated in a schematic form in Fig. 2, which summarizes some of the findings of this study. Knowledge of the energy balance over oceans is critical, for example, for the coupling of 3 dimensional dynamical models of the ocean and the atmosphere, and the related exchange of energy and water at the ocean atmosphere interface. Accurate knowledge of the surface energy fluxes at the atmosphere/ocean interface is also critical for the determination of the ocean heat budget and transports of heat in the ocean (Trenberth and Caron 2001; Trenberth and Fasullo 2008). The energy balance over land is of eminent importance for the representation of land surface processes in Earth system models and the determination of climate and ecology of the immediate human environments (e.g., Seneviratne et al. 2010). The considerable uncertainties and lack of agreed-upon reference values particularly of the surface flux components of the land and ocean energy balances have traditionally hampered the coupling of land surface and ocean models to the atmospheric component. In the present study we try to use the information contained in direct observations to pose additional constraints on these budgets over land and oceans. As in Wild et al. (2013a), the approach taken here relies on a combination of direct observations and modeling results performed within the Coupled Model Intercomparison Project Phase 5 (CMIP5) for the latest 5th IPCC assessment report (IPCC-AR5). This goes along with a validation of the land and ocean energy budgets of the comprehensive set of climate models that is now available in the CMIP5 archive. Compared to Wild et al. (2013a) more than twice the number of climate models were available in the CMIP5 archive for the present study. Emphasis in the present study is placed on the land surface energy balance, which is best constrained by direct surface observations, since the vast majority of direct flux measurements are taken over land surfaces. In addition and for completeness, an attempt is made to derive estimates for the energy bal (...truncated)