Dimethyl sulfide (DMS) is one of many biologically derived gases and particles emitted from the ocean that has the potential to affect climate. In the case of DMS it is oxidized to sulfate, which increases the aerosol loading in the atmosphere either through nucleation or condensation on other aerosols, which in turn changes the energy balance of the Earth by reflection of sunlight either through direct reflection by the aerosols or by modifying clouds. We have previously shown that the geographical distribution of DMS emission from the ocean may be quite sensitive to climate changes, especially in the Southern Ocean.  

Our state-of-the-art sulfur-cycle Earth system model (ESM), based on the Community Earth System Model (CESM) climate model, includes an ocean sulfur ecosystem model, the oxidation of DMS to sulfate by atmospheric chemistry, and the indirect effect of sulfate on radiation via clouds using the Modal Aerosol Model (MAM).

Our multi-decadal simulations calculate the impact of DMS on the energy balance and climate of the Earth system, and its sensitivity/feedback to climate change.  The estimate from our simulations is that DMS is responsible for ~6 W/m2 of reflected sunlight in the pre-industrial era (globally averaged), and ~4 W/m2 in the present era.  The reduction is caused by increased competition with cloud condensation nuclei from anthropogenic aerosols in the present era, and therefore partially offsets the cooling from the anthropogenic aerosols.  The distribution of these effects are not uniform, and doesn’t necessarily follow the simulated DMS distribution, because some clouds are more sensitive to DMS derived sulfate than others, and there are surface feedbacks such as the ice-albedo feedback.  Although our calculated impact of DMS is higher than some previous studies, it is not much higher than recent observational estimates (McCoy, et al., 2015).

We are now porting these capabilities to the US Department of Energy’s Accelerated Climate Modeling for Energy (ACME) model.