1Kuopio Unit, Finnish Meteorological Institute, Kuopio, Finland
2School of Earth and Environment, University of Leeds, Leeds, UK
3Department of Law, University of Eastern Finland, Joensuu Campus, Joensuu, Finland
4Climate change, Finnish Meteorological Institute, Helsinki, Finland
5Department of Physics, University of Helsinki, Helsinki, Finland
6Department of Applied Physics, University of Eastern Finland, Kuopio campus, Kuopio, Finland
7School of Physical and Chemical Sciences, North-West University, Potchefstroom Campus, Potchefstroom, South Africa
Abstract. Aerosol particles from shipping emissions both cool the climate and cause adverse health effects. The cooling effect is, however, declining because of shipping emission controls aiming to improve air quality. We used an aerosol-climate model ECHAM-HAMMOZ to test whether by altering ship fuel sulfur content, the present-day aerosol-induced cooling effect from shipping could be preserved while at the same time reducing premature mortality rates related to shipping emissions. We compared the climate and health effects of a present-day shipping emission scenario with (1) a simulation with strict emission controls in the coastal waters (ship fuel sulfur content of 0.1%) and twofold ship fuel sulfur content compared to current global average of 2.7% elsewhere; and (2) a scenario with global strict shipping emission controls (ship fuel sulfur content of 0.1% in coastal waters and 0.5% elsewhere) roughly corresponding to international agreements to be enforced by the year 2020. Scenario 1 had a slightly stronger aerosol-induced radiative flux perturbation (RFP) from shipping than the present-day scenario (−0.43 W m−2 vs. −0.39 W m−2) while reducing premature mortality from shipping by 69% (globally 34 900 deaths avoided per year). Scenario 2 decreased the RFP to −0.06 W m−2 and annual deaths by 96% (globally 48 200 deaths avoided per year) compared to present-day. A small difference in radiative effect (global mean of 0.04 W m−2) in the coastal regions between Scenario 1 and the present-day scenario imply that shipping emission regulation in the existing emission control areas should not be removed in hope of climate cooling. Our results show that the cooling effect of present-day emissions could be retained with simultaneous notable improvements in air quality, even though the shipping emissions from the open ocean clearly have a significant effect on continental air quality. However, increasing ship fuel sulfur content in the open ocean would violate existing international treaties, could cause detrimental side-effects, and could be classified as geoengineering.