CO2-forced changes of Arctic temperature lapse rates in CMIP5 models

Abstract

Global climate models show that the lapse rate feedback is a key reason for Arctic amplification of global warming. However, a proper assessment of the underlying spatial and temporal structure of the vertically non-uniform temperature change is still lacking. In this study we use the output from several CMIP5 climate models to investigate the Arctic lapse rate change in the context of global warming forced by CO2. Comparisons between the perturbed and unperturbed states show that in the Arctic the temperature increases more near the surface than aloft, especially over ice-covered ocean and Arctic land. The bottom-heavy warming is most pronounced in boreal winter and is also seen in spring and autumn but to a lesser extent. The atmosphere over these areas is characterised by an inversion layer. We find that the inversion strength in the unperturbed climate and the change of the temperature lapse rate from unperturbed to perturbed state correlate to each other across the model ensemble over ice-covered ocean, open ocean and for sea ice retreat regions. However, the models simulate no correlation for the entire Arctic. Further investigation of the surface energy budget for models with weak and strong inversion strengths, respectively, show that the surface energy storage and the increase of turbulent heat fluxes which enhance the downward longwave radiation contribute most to the warming at the surface.

Keywords

• arctic amplification
• lapse rate feedback
• inversion strength
• arctic surface energy budget