Erlangen 2018 – scientific programme

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UP: Fachverband Umweltphysik

UP 4: Climate modelling

UP 4.1: Talk

Monday, March 5, 2018, 14:00–14:15, G 1.011

An explanation for the different climate sensitivities of land and ocean surfaces based on the diurnal cycle — •Axel Kleidon and Maik Renner — Max-Planck-Institut für Biogeochemie, Jena

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 to show that predictions compare very well with observations and CMIP 5 climate model simulations.