Importance of including the marine perspective in assessments of ship emissions

Baltic Rim Economies

Erik Ytreberg,
Associate Professor in Maritime Environmental Science,
Department of Mechanic and Maritime Sciences, Chalmers University of Technology,
Gothenburg, Sweden

International shipping is essential to the world economy and the International Maritime Organization (IMO) estimates 90% of the world’s trade to be carried by sea. Shipping is however causing multiple pressures on the atmosphere and the marine environment via engine exhausts and emissions from different waste streams containing chemicals and nutrients. The methodology on how ship emissions impact air quality and human health are well established and used in cost-benefit analysis of policy proposals. However, the knowledge base is not equally established for the marine environment. This risk policies to be biased towards air pollution whilst trading off impacts on the marine environment.

A current example is the wide-scale use of exhaust gas cleaning systems, also known as scrubbers. Globally, over 4000 ships are equipped with scrubbers, which is an abatement technology to reduce sulphur oxide emissions to air. Scrubbers can be operated in open or closed loop mode. Open loop systems, which is the most popular chose by shipowners, use seawater to wash sulphur oxide out of the exhaust, and the resulting washwater is discharged back to the sea. Closed loop systems recirculate the washwater and produces a lower volume of discharge water. Scrubbers were introduced on the market as an abatement method to meet the global cap of maximum allowable sulphur content in marine fuel which in 2020 was reduced from 3.5% to 0.5%. To comply with the stricter regulations and reduce the atmospheric emissions of sulphur oxides, the ship owner can either

  • switch from high sulphur fuel oil (HFO) to distillates e.g. marine gas oil
  • retrofit vessel to use alternative fuels, such as liquified natural gas and methanol
  • install a scrubber and continue the use of the relatively cheaper HFO.

In the recent publication by Ytreberg et al (2021), we developed a comprehensive framework to analyze how different pressures from shipping degrade marine ecosystems, air quality and human welfare. By adding knowledge from marine ecotoxicology and life-cycle analysis to the existing knowledge from climate, air pollution and environmental economics we established a conceptual framework that enabled a valuation of the damage costs associated with specific types of environmental and human health degradation. The results for a Baltic Sea case showed the total annual damage costs of Baltic Sea shipping to be 2.9 billion €. The damage costs due to impacts on marine eutrophication (800 million €) and marine ecotoxicity (600 million €) were in the same range as the combined damage costs associated with reduced air quality (800 million €) and climate change (700 million €).

The results highlight the importance to include the marine perspective in future socio-economic studies of ship emissions. However, solutions already exist to reduce the input of chemicals and nutrients which are the main pollutants causing marine ecotoxicity and marine eutrophication. The three most important are:

  • installing a selective catalytical system (SCR) which reduces the level of nitrogen oxide in the exhaust gas from the engine
  • changing antifouling system from toxic copper-based antifouling paints to biocide-free paints
  • operate scrubbers in closed loop mode.

These three measures would reduce emissions of chemicals and nitrogen, and the corresponding damage costs due to marine ecotoxicity and marine eutrophication, by 95% and 70%, respectively. Moreover, the efficacy of biocide-free foul-release paints to prevent organisms to attach to the ship hull has increased substantially in the last couple of years. For example, several studies in the Baltic Sea region have shown these paints to be as effective as toxic copper-based paints. Despite this, only a handful of ships in the Baltic Sea use foul-release paints and as long as copper-based paints are allowed to be used, biocide-free strategies have difficulty in gaining market shares.

The results also showed the use of open loop scrubbers to be a major source of several metals and PAHs to the Baltic Sea. By switching to closed loop mode, which 85% of the Baltic Sea scrubber fleet has the possibly to do, the input of PAHs and metals from scrubbers could be reduced with up to 90%. Based on all these findings we strongly recommend the legislators on global (IMO), EU and national level to include the marine perspective in future socio-economic assessments of ship emissions.

Email: erik.ytreberg@chalmers.se

Expert article 3119

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