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https://doi.org/10.5194/esd-2017-44
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
19 May 2017
Review status
This discussion paper is under review for the journal Earth System Dynamics (ESD).
An explanation for the different climate sensitivities of land and ocean surfaces based on the diurnal cycle
Axel Kleidon and Maik Renner Biospheric Theory and Modelling Group, Max-Planck-Institut für Biogeochemie, Jena, Germany
Abstract. Observations and climate model simulations consistently show a higher climate sensitivity of land surfaces compared to ocean surfaces, with the cause for this difference being still unclear. Here we show that this difference in temperature sensitivity can be explained by the different means by which the diurnal variation in solar radiation is buffered. While ocean surfaces buffer the diurnal variations by heat storage changes below the surface, land surfaces buffer it mostly by heat storage changes above the surface in the lower atmosphere that are reflected in the diurnal growth of a convective boundary layer. Storage changes below the surface allow the ocean surface-atmosphere system to maintain turbulent fluxes over day and night, while the land surface-atmosphere system maintains turbulent fluxes only during the daytime hours when the surface is heated by absorption of solar radiation. This shorter duration of turbulent fluxes on land then results in a greater sensitivity of the land surface-atmosphere system to changes in the greenhouse forcing because nighttime temperatures are then shaped by radiative exchange only, which are more sensitive to changes in greenhouse forcing. We use a simple, analytic energy balance model of the surface-atmosphere system in which turbulent fluxes are constrained by the maximum power limit to estimate the effects of these different means to buffer the diurnal cycle on the resulting temperature sensitivities. The model predicts that land surfaces have a 50% greater climate sensitivity than ocean surfaces, and that the nighttime temperatures on land increase about twice as much as daytime temperatures because of the absence of turbulent fluxes at night. Both predictions compare very well with observations and CMIP 5 climate model simulations. Hence, the greater climate sensitivity of land surfaces can be explained by its buffering of diurnal variations of solar radiation in the lower atmosphere.

Citation: Kleidon, A. and Renner, M.: An explanation for the different climate sensitivities of land and ocean surfaces based on the diurnal cycle, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-44, in review, 2017.
Axel Kleidon and Maik Renner
Axel Kleidon and Maik Renner
Axel Kleidon and Maik Renner

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Short summary
We provide an explanation why land temperatures respond more strongly to global warming than ocean temperatures, a robust finding in climate models that has so far not been understood well. We explain it by the different ways by which ocean and land surfaces buffer the strong variation in solar radiation and demonstrate this with a simple, physically-based model. Our explanation also explains why nighttime temperatures warm more strongly, another robust finding of global warming.
We provide an explanation why land temperatures respond more strongly to global warming than...
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