Shipping sector faces emissions dilemma

The inherent difficulty in cutting both toxic emissions from ships and their global warming impact are highlighted in a new study that underlines the incompatibility of these goals. Shipping is estimated to contribute just over 3 per cent of total greenhouse gas emissions worldwide, but this only half the climate-impact story of the sector.

Because of emissions of other gases in bunker fuels, the overall effect from shipping is a cooling one not a warming one, Jan Fuglestvedt from the Center for International Climate and Environmental Research Oslo (CICERO) told Reuters. While carbon dioxide emissions from burning bunker fuel add to greenhouse gases like any other fossil fuel, the sulphur dioxide (SO₂) also emitted causes water droplets to form around it in the atmosphere. This increases cloud formation and clouds reflects solar radiation back into space.

The problem is that this global cooling gas is also highly toxic. So, as efforts to clean up the poisonous emissions of ships take hold, shipping’s overall climate impact will shift from cooling toward warming, Fuglestvedt and colleagues wrote in a paper published last week in the journal Environmental Science and Technology. But the case for doing so appears compelling. A previous study estimated that toxic sulphur dioxide from bunker fuel led to the deaths of 60,000 people worldwide in 2001 from cancer and disease of the heart and lungs.

The Fuglestvedt study argues that maintaining or increasing sulphur emissions from ships to fight global warming can’t be justified. It also estimates, however, that a shift to net warming would take many decades. Even if sulphur dioxide emissions were reduced by 90 per cent in the next few years it would take about 70 years for shipping to become a net contributor to global warming, all other things being equal.

The International Maritime Organization is pushing for cuts in the sulphur content of bunker fuel to no more than 3.5 per cent from 4.5 per cent by 2012 and then to just 0.5 per cent by 2020. In busy northern European shipping channels, the limit will be just 1.5 per cent from 2010.

The US Environmental Protection Agency (EPA) signalled a move on toxic emissions from ships in March, proposing laws to lift fuel quality standards in new ships and, along with Canada, asking the IMO to create a 200 nautical mile clean-fuel buffer zone off their coastlines. Last week, the EPA published its draft rule on fuel standards to substantially cut nitrogen oxide and SO₂ emissions by 2016, the New York Times reports.

The UN climate conference in Copenhagen will consider measures to bring the shipping sector into a new global agreement to cut carbon emissions. Emissions trading, fuel taxes and clean-technology innovation measures are all in the mix.