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In this study, we use the National Center for Atmospheric Research Community Earth System Model to investigate the contribution of sea ice and land snow to the climate sensitivity in response to increased atmospheric carbon dioxide content. We focus on the overall effect arising from the presence or absence of sea ice and/or land snow. We analyze our results in terms of the radiative forcing and climate feedback parameter. We find that the presence of sea ice and land snow decreases the climate feedback parameter (and thus increases climate sensitivity). Adjusted radiative forcing from added carbon dioxide is comparatively less sensitive to the presence of sea ice or land snow. The effect of sea ice on the climate feedback parameter decreases as sea ice cover diminishes at higher CO2 concentration. However, the influence of both sea ice and land snow on the climate feedback parameter remains substantial under the CO2 concentration range considered here (to eight times preindustrial CO2 content). Approximately, one quarter of the effect of sea ice and land snow on the climate feedback parameter is a consequence of the effect of these components on longwave feedback that is mainly associated with cloud change. Polar warming in response to added CO2 is approximately doubled by the presence of sea ice and land snow. Relative to the case in which sea ice and land snow are absent in the model, in response to increased CO2 concentrations, the presence of sea ice and land snow results in an increase in global mean warming by over 40%.

Plain Language Summary Sea ice and land snow are two crucial components that affect the climate response to external forcings. Feedbacks between ice/snow and climate change cause amplified surface warming in high latitudes. In this study, we use a climate model to estimate the contribution of sea ice and land snow to climate change in response to increased CO2 concentrations. We compare the climate response to increased CO2 between the simulations with sea ice and/or land snow and the simulations without them. We show that the existence of sea ice and land snow substantially amplifies the global temperature response to increased CO2 with sea ice having a stronger effect than land snow. Under higher CO2 levels, the effect of sea ice diminishes more rapidly than does the effect of land snow. About one quarter of the total climate feedback from sea ice and land snow is associated with the change in longwave radiation. Also we show that the effect of sea ice and land snow on the sensitivity of top-of-atmosphere net energy flux to the global mean temperature change is approximately additive.