Emissions of air pollutants and greenhouse gases from the shipping sector have increased substantially in the last two decades, contributing to both climate change and air pollution problems, according to a report from the European Environment Agency (EEA).

The shipping sector needs an integrated monitoring, reporting and verification system for emissions in European waters to systematically address both types of emissions together, the report says.

Air pollutants emitted by shipping can affect air quality in many areas, particularly around ports and busy shipping channels. The release of greenhouse gases and air pollutants from international shipping has a complex effect on the climate - greenhouse gas emissions have a warming effect, while on the other hand some air pollutants lead to cooling.

Jacqueline McGlade, EEA Executive Director, said: “This study shows the complex effects different emissions are having on the planet. We need initiatives that protect the environment as an overall system. The choice between either clean air or mitigating climate change is a false dichotomy - Europe needs both. By avoiding unnecessary movement of goods and improving transport efficiency, we can address both air pollution and greenhouse gas mitigation together.”

At the global level, the combined emissions from ships have a net cooling effect on the climate, according to recent scientific literature. This is because these aerosols directly scatter some radiation and indirectly lead to cloud formation. The overall cooling effect is rather uncertain. Nevertheless, it seems that the cooling effect of aerosols is currently larger than the warming effect of greenhouse gas emissions.

The EEA has also carried out a model simulation which shows that the direct aerosol cooling effect may be slightly reduced by new EU rules on sulphur content in ship fuels. However, there is still some uncertainty as changes in cloud formation and other direct and indirect effects are not taken into account in this modeling.

Shipping’s air pollution problem

Compared to other economic sectors, shipping is currently one of the most unregulated sources of air pollution. The report highlights that some success has been achieved through EU legislation, especially on sulphur content of marine bunker fuels where limits are stricter than the international standards.

Air pollution from shipping harms health, increasing heart disease, respiratory illnesses and premature death in some cases. Some of these air pollutant emissions also damage the environment through acidification and eutrophication.

While some air pollutants are emitted far from land, around 70 % of the global emissions from ships are within 400 km of coastlines, and this rate is much higher in European waters. Moreover, some pollutants from ships can travel hundreds of kilometres in the atmosphere.

In some areas, ships can contribute up to 20-30% of the local fine particulate matter (PM2.5) concentrations. Around some busy ports and shipping channels ships can contribution as much as 80 % of nitrogen oxide (NOx) and sulphur dioxide (SO2) pollution. The report highlights that there are relatively few measurement data available to attribute shipping’s contribution to local air pollution, although there are some modelling studies.

Shipping and carbon emissions

In 2007 national and international shipping was responsible for 3.3 % of global carbon dioxide (CO2) emissions - and around 30 % of this is emitted on routes passing through European ports. Emissions from the sector are projected to grow by up to 4 % per year over the next decade.

There is a clear link between economic growth and the movement of goods, so emissions from shipping currently change in step with the level of economic activity. Carbon dioxide emissions from international shipping departing from EU ports, for example, increased by approximately 35 % between 1990 and 2010.

Other key pollutants have increased between 35 and 55 % over the same period. However, most emissions types have decreased since 2006, possibly due to the economic downturn and the legislation reducing SO2 levels.

Curbing air pollution and greenhouse gases together

The report shows that reducing fuel consumption is the best way to reduce emissions. Better fuel efficiency may be the easiest way to cut both air pollution and greenhouse gases, the report says, recommending technical improvements and also different ship operating procedures.

If ships reduced their speed by 10 %, known as ‘slow steaming’, it could cut energy demand by approximately 19 %, according to one study. Some shipping sectors are already switching to liquid natural gas (LNG), leading to an eradication of SO2 emissions, 80 % reduction of NOx and 20 % reduction of CO2.

Environmental legislation

Against the background of challenges presented by global trade operations, ships registered in many different countries and marine fuel bunkered in any location in the world, there is currently considerable debate on the regulation of emissions from the shipping sector.

The report provides an overview of the various topics that need to be addressed, ranging from ship registration to atmospheric modelling of air quality and climate impacts.