Black carbon in the Arctic

The final frontier for emissions control may be international shipping, which operated independent of controls on its engine exhaust emissions until just three years ago, when regulations on the sulfur content of international marine fuel went into effect to limit emissions of particulate matter.

Such measures are signs of environmental progress in the marine sector, but they leave a significant share of emissions unregulated. One of the most important omissions is black carbon, which a study recently concluded is the second most important contributor global climate change. Its effects are particularly potent near ice and snow, which are of course abundant in the Arctic. The Arctic region has been warming at twice the global rate, and sea ice is melting at unprecedented levels, so controls on black carbon should be a high priority for those concerned about impacts on Arctic climate.

The International Maritime Organization (IMO), which is responsible for regulating international shipping emissions, recently took its first action toward addressing the impacts of black carbon on the Arctic. At the 62nd meeting of the Marine Environment Protection Committee, member states adopted a research agenda that includes collation of potential control measures.

No research published to date has quantified just how big the impact of shipping is or could be on the Arctic. But we are getting closer. A study I co-authored that was just published in in the journal Atmospheric Chemistry and Physics quantified the radiative forcing of international shipping emissions with a special focus on the Arctic. Radiative forcing is a measure of energy absorption in the atmosphere that scientists use as a rough proxy for a temperature impacts.

The study suggests that black carbon emissions released from ships in Arctic waters in 2030 will indeed cause Arctic warming, which would be equivalent to about 15 mW/m-2 in the spring season under a high growth scenario. The study also found that under the same high-growth trajectory, ozone concentrations generated by NOx shipping emissions would cause even greater warming, equivalent to approximately 19 mW/m-2 in the spring season. The fall season is when the radiative forcing caused by ozone would be more than double any other component emitted by Arctic shipping. The study did not look at the impacts on the Arctic from shipping outside the region, but in a sensitivity analysis two-thirds of the ozone generated in the high growth trajectory came from emissions within the Arctic. The rest was due to transport from lower latitudes.

The study evaluated the potential benefits of a 70% reduction in black carbon emissions from in-Arctic shipping based on a review of technically feasible control measures. The climate model showed this would reduce in-Arctic warming by approximately one-third when compared against a high-growth scenario. Additional warming could potentially be avoided by controls on in-Arctic NOx emissions, but these were not evaluated.

In summary, the study found that for those concerned about the impacts on the Arctic from future shipping in Arctic waters, black carbon and ozone precursors, particulary NOx, are the two components to worry about. While the IMO does not yet have a mechanism to regulate black carbon, a policy instrument called an Emission Control Area (ECA) does exist for NOx control. Member states to the IMO can apply for a NOx ECA, and we suggest this should be considered for the Arctic.

This study points toward some interesting areas for future research. First, the suggestion that ozone has a strong Arctic impact should lead to an exploration of the potential climate benefit of NOx controls on Arctic shipping, especially an Arctic ECA. Furthermore, the relationship between the location of NOx and black carbon emissions and their impacts on the Arctic should be explored to understand just how far outside the Arctic these controls should be considered.

On the emissions inventory side, the black carbon emission factors are based on a very limited set of real-world measurements and likely lead to an underestimate of global shipping emissions as acknowledged in the paper. Some work to improve the quality and resolution of emission factors, particularly for ships of various engine sizes, under various engine loads and using various fuels would help. On the climate modeling side, it would be important to ensure that the radiative forcing parameterizations for black carbon are aligned with the recently published black carbon bounding assessment. Also, my co-authors suggest that the chemistry of ship plumes needs a higher resolution of analysis, so this would be worth some further exploration.

The study was led by Stig Dalsoren, senior research fellow at the Center for International Climate and Environmental Research in Oslo. The other coauthors included international shipping emissions experts James Corbett of the University of Delaware and Daniel Lack ,with the NOAA Earth Systems Research Laboratory. They provided the in-Arctic emissions initially published in 2010, in a study co-funded by the ICCT.