The commercial fleet pollutes a great deal when ships are berthed in ports. The OECD has published a new analysis reviewing exactly how much.

The analysis shows that the global fleet in 2011 - the latest year in which data has been gathered - sent 18 million tons CO2 into the atmosphere, 0.40 million tons NOx and 0.2 million tons SOx. Emissions in ports account for two percent of all emissions from ships. Two ship types are the biggest sinners in terms of the various forms of emissions, says the OECD.