Ship pollution is slowing global warming
18/3/2010 News Scientist Ship pollution is slowing global warmingPolluting ships
ENVIRONMENTAL paradoxes don’t come much bigger. In July this year, the world’s shipping lines
will begin to apply pollution-cutting rules that will save tens of thousands of lives a year.
Yet these very measures – which will radically cut sulphur emissions from ships – have a downside: they will also increase global warming.
When it meets next week, the Marine Environment Protection Committee of the International Maritime Organization (IMO),
the UN body that regulates world shipping, will not even be discussing setting limits on regulating the carbon emissions of shipping.
Yet it will confirm plans to slash the permitted sulphur content of fuel oil burned by most of the world’s ships.
Sulphur dioxide (SO2) emissions will diminish by as much as 90 per cent, and with them the resulting haze of sulphate particles.
That’s where the problem lies. By shading the planet, the haze partially masks the warming effects of greenhouse gases
such as carbon dioxide also produced by the world’s fleet of 100,000 ships. Almost a billion tonnes of CO2
are emitted annually by shipping, some 3 per cent of the global total, and it was originally planned that measures
to reduce these emissions would also be introduced at next week’s meeting.
Those plans are now on hold. As a result, the world is set to suffer a double warming effect from shipping,
says Jan Fuglestvedt of the Centre for International Climate and Environmental Research in Oslo, Norway:
“one from CO2 and one from the reduction of SO2″ (Environmental Science & Technology, vol 43, p 9057).
Shipping lags behind most other industries in tackling sulphur pollution. Emissions from power stations,
road vehicles and other land-based sources have been reduced to very low levels both for health reasons
and to curb acid rain. But ships can still burn fuel containing 4.5 per cent sulphur; for European cars the limit is 0.001 per cent.
Just 16 large ships could emit as much SO2 as all the world’s cars.
Two years ago, the IMO agreed a plan to cut the emissions of SO2 from the world’s fleet. The plan,
which comes into force in July, will cut the maximum sulphur content of shipping fuel to 3.5 per cent in 2012
and 0.5 per cent by 2020. Special sulphur emission control areas around the coastlines of North America
and in the Baltic and North seas set lower limits: 1 per cent from this July and 0.1 per cent by 2015.
The net effect of the warming and cooling influences of shipping currently neutralises about 7 per cent of
human-produced global warming. That is about to end as the new rules will cut global sulphur emissions from shipping,
and with it their cooling effect, by 80 to 90 per cent in the coming decade.
Few policy issues are more complex than the effects of carbon and sulphur emissions from shipping,
partly because one contributes to global warming while the other has the opposite effect, and also because
the impacts of CO2 and SO2 emissions are felt on very different timescales.
Few policy issues are more complex than the effects of carbon and sulphur emissions from shipping
The climatic effect of emissions from a typical ship at sea is initially dominated by the strong cooling influence of the SO2.
As well as providing a direct shading effect, sulphate particles also act as nuclei around which water droplets form,
making skies cloudier. Direct SO2 shading from today’s shipping is estimated to cool the planet by 31 milliwatts per square metre.
Though hard to model precisely, the influence on cloud formation is likely to be three times that.
But the SO2 only stays in the air for a few days. If it were not constantly replaced, the warming effect of the ships’ CO2 emissions
would quickly dominate. This lasts for centuries. The accumulated CO2 emissions of two centuries of steam shipping
are currently heating the planet by 37 milliwatts per square metre. But at the moment, the overall effect is to cool the planet.
As more and more CO2 accumulates in the air from shipping, however, warming will come to dominate. The only question is when.
Veronika Eyring of the Institute for Atmospheric Physics in Wessling, Germany, says that if emissions remain
as they are today, the tipping point is 50 years away. The reductions in sulphur emissions planned for the next decade
will push shipping into a net warming influence within that period (Atmospheric Environment, DOI: 10.1016/j.atmosenv.2009.04.059).
There is little chance of the controls on SO2 being reversed – and with good reason. James Corbett of the University
of Delaware at Newark estimates that it currently kills around 64,000 people a year worldwide from lung and heart disease,
of which some 27,000 are in Europe.
Any hopes that the IMO would act on CO2 at the same time as cutting SO2 emissions evaporated with the failure
of climate talks in Copenhagen in December. The IMO now says it awaits a UN lead.
Who’s responsible?
It could be a long wait. Like air transport, shipping was left out of the 1997 Kyoto protocol. Nor was there any
mention of shipping in the Copenhagen accord, intended as a blueprint for what should replace the Kyoto protocol in 2012,
which was signed by more than 20 world leaders.
Admittedly, setting CO2 emissions targets for international shipping is not easy. As with airlines, it is not obvious
which country should be responsible, but for shipping the problem is made worse by the popularity of flags of convenience.
Two-thirds of the world’s ships are registered in small non-industrial countries such as Panama and the Bahamas that do not have national emissions targets.
One proposed solution is to treat the entire industry as if it were a single country, with its own emissions ceiling.
Developing countries say this would be unfair, because it undermines the principle that the industrialised nations
should bear the brunt of emissions targets. Another suggestion is to create a tax whose revenues would go to
developing nations, but the US and China have so far both opposed it.
There is huge potential to cut CO2 emissions from shipping. The Danish shipping line Maersk claimed last month
that by making its massive container ships travel more slowly it had cut their fuel use, and hence carbon emissions, by 30 per cent.
The International Chamber of Shipping, an industry association, says better-designed engines, hulls and
propellers could cut CO2 emissions by a further 15 to 20 per cent. And waiting in the wings are biofuels,
currently being trialled by Maersk, solar panels, nuclear reactors and even a return to sailing, using giant kites.
But without a cap on shipping emissions, much of this may not happen. If it doesn’t, CO2 emissions from shipping are predicted to triple by 2050.
That brings closer the possibility that the world will one day need to take emergency action to stave off runaway climate change.
One of the most effective ways of cooling the planet, suggested by Nobel prizewinning atmospheric chemist
Paul Crutzen, might then be to spray the atmosphere with sulphur. In other words, to do exactly what shipping is doing today.
“SO2 emissions are a form of inadvertent geoengineering,” says Fuglesvedt. Wouldn’t it be weird, he suggests, if we cleaned up the ships and then were forced to spend billions of dollars to do just what they have been doing for free?
Wouldn’t it be weird if we were forced to spend billions to do what ships have been doing for free?
Good intentions, unforeseen results
Sulphur dioxide is not the only pollutant that has beneficial effects, and sometimes measures intended to
protect the environment can have unexpected negative consequences.
Treating sewage
Untreated sewage kills fish by generating oxygen-depleted dead zones, but it also provides food for some bird species.
One study in 2001 found that after a sewage treatment plant came on stream, the number of gulls in the affected area fell by 93 per cent.
Cutting carbon dioxide
The arch-villain of climate change may be boosting growth in some plants. In chambers where levels of CO2
have been deliberately boosted, plants have been shown to grow up to 40 per cent faster than normal.
Recycling paper
According to a 1996 study, it may actually be less harmful to burn magazines than to recycle them.
De-inking paper in order to recycle it leaves a toxic sludge of heavy metals.
Mending the ozone hole
In the 1970s, high levels of CFCs in the atmosphere caused a damaging thinning of the ozone layer.
This has cooled the air over east Antarctica, and temperature rises in the region are predicted to accelerate as the hole heals following a ban on CFCs.
Hydropower
Rotting vegetation in newly flooded reservoirs can emit methane – a powerful greenhouse gas.
Dissolved methane builds up and is released when water passes through the dam’s turbines.
Shanta Barley
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