labs_title
Caldeira Lab

Estimating the Contribution of Sea Ice Response to Climate Sensitivity in a Climate Model

Ken Caldeira & Ivana Cvijanovic

Caldeira, K. and I. Cvijanovic, Estimating the Contribution of Sea Ice Response to Climate Sensitivity in a Climate Model, 2014: J. Climate, 27, 8597–8607, doi:10.1175/JCLI-D-14-00042.1.

Abstract

The response of sea ice to climate change affects Earth’s radiative properties in ways that contribute to yet more climate change. Here, a configuration of the Community Earth System Model, version 1.0.4 (CESM 1.0.4), with a slab ocean model and a thermodynamic–dynamic sea ice model is used to investigate the overall contribution to climate sensitivity of feedbacks associated with the sea ice loss. In simulations in which sea ice is not present and ocean temperatures are allowed to fall below freezing, the climate feedback parameter averages ~1.31W m-2K-1; the value obtained for control simulations with active sea ice is ~1.05W m-2K-1, indicating that, in this configuration of CESM1.0.4, sea ice response accounts for ~20% of climate sensitivity to an imposed change in radiative forcing. In this model, the effect of sea ice response on the longwave climate feedback parameter is nearly half as important as its effect on the shortwave climate feedback parameter. Further, it is shown that the strength of the overall sea ice feedback can be related to 1) the sensitivity of sea ice area to changes in temperature and 2) the sensitivity of sea ice radiative forcing to changes in sea ice area. An alternative method of disabling sea ice response leads to similar conclusions. It is estimated that the presence of sea ice in the preindustrial control simulation has a climate effect equivalent to ~3W m-2 of radiative forcing.

Figure 4. Loss of all sea ice would add 3 W/m2 to climate forcing, almost as much as a doubling of CO2. Sea ice radiative forcing as a function of zero-ice area. Values of sea ice radiative forcing are estimated by calculating the amount of radiative forcing needed in the zero-ice and prescribed-ice simulations, respectively, to achieve the same global mean temperature as in the active-ice simulations. For the prescribed-ice cases, relative sea ice area is calculated as area in the prescribed-ice simulations minus the area in the active-ice simulations. For the zero-ice cases, relative sea ice area is calculated as the amount in the active-ice simulations minus the amount in the zero-ice simulations. Slopes of the lines indicate that loss of sea ice produces about 0.1 W m−2 of sea ice radiative forcing for each 1012 m2 of sea ice loss.