Arctic Climate Response to Aerosols on Sea Ice and Snow in CESM

The influence of aerosols, such as black carbon, on snow and ice albedo may be responsible for a significant portion of the high northern latitude climate change in the past century. To investigate their role, aerosol cycling and optics have been incorporated into CESM for black carbon, organic carbon, and dust on terrestrial snow and sea ice. The role of the aerosols in snow and ice in the model for the year 2000 is to warm the surface annually by roughly 0.5 deg C where there is seasonal snow cover and 0.5 to 1 deg C over sea ice. We will discuss the radiative effects and climate response of aerosols from a series of sensitivity studies to assess the role of individual aerosol types. Although some fires are natural and some dust mobilization is anthropogenic, we separate dust from black and organic carbon for the purposes of distinguishing the relative amount of forcing from these sources. We will also discuss the response of Arctic climate to the snow and sea ice albedo feedbacks associated with black carbon and other light absorbing aerosols in the model. CESM also includes new characterizations of atmospheric aerosols, which motivate us to consider whether the same level of complexity has an impact on snow and sea ice albedos. Therefore we will also examine the sensitivity of the radiative forcing to the optical properties chosen to represent aerosols on snow and sea ice.