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Pollution from ships can make the waters of heavily trafficked trade routes more acidic, and may contribute to local acidification on a scale similar to that resulting from increased atmospheric carbon dioxide.

David Turner at the University of Gothenburg in Sweden and his colleagues modelled the effects of shipping emissions in the world's waters using grids of 1 degree longitude and latitude. This fine detail suggested that ships' emissions of sulphur oxide and nitrogen oxide acidify the water in some busy Northern Hemisphere coastal areas by up to 0.002 pH units each summer. Regulations that allow ships to reduce emissions to the air by 'scrubbing' fuel exhaust with sea water may accelerate acidification by transferring acid to surface waters.

Although not a significant driver of ocean acidification globally, shipping acidification could be a concern where high traffic occurs near fisheries or important regions of marine biodiversity, the authors say.

Geophys. Res. Lett. 40, 2731–2736 (2013)