© Getty Images
Cutting the speed of ships has huge benefits for humans, nature and the climate, according to a new report.
A 20% reduction would cut greenhouse gases but also curb pollutants that damage human health such as black carbon and nitrogen oxides.
This speed limit would cut underwater noise by 66% and reduce the chances of whale collisions by 78%.
UN negotiators will meet in London this week to consider proposals to curb maritime speeds.
Ships, of all sorts and sizes, transport around 80% of the world's goods by volume. However they are also responsible for a significant portion of global greenhouse emissions thanks to the burning of fuel.
Shipping generates roughly 3% of the global total of warming gases - that's roughly the same quantity as emitted by Germany.
While shipping wasn't covered by the Paris climate agreement, last year the industry agreed to cut emissions by 50% by 2050 compared to 2008 levels.
This new study, carried out for campaign groups Seas at Risk and Transport & Environment builds on existing research that suggests that slowing down ships is a good idea if you want to curb greenhouse gases.
The report though also considers a range of other impacts of a speed cut such as on air pollution and marine noise.
As ships travel more slowly they burn less fuel, which means there are also savings in black carbon, sulphur and nitrogen oxides. The last two in particular have serious impacts on human health, particularly in cities and coastal areas close to shipping lanes.
The report found that cutting ship speed by 20% would cut sulphur and nitrogen oxides by around 24%. There are also significant reductions in black carbon, which are tiny black particles contained in the smoke from ship exhausts. © Getty ImagesSlowing ships down would cut the amount of fuel burned
Cutting black carbon helps limit climate warming in the Arctic region because when ships burn fuel in the icy northern waters, the particles often fall on snow, and restrict its ability to reflect back sunlight, which accelerates heating in the Arctic region.
The study also says that a 20% cut in speed would reduce noise pollution by two thirds - while the same speed limitation would reduce the chances of a ship colliding with a whale by 78%.
"It's a massive win, win, win, win," said John Maggs from Seas at Risk.
"We've got a win from a climate point of view, we've got a win from a human health point of view, we've got a win for marine nature, we've got a potential safety gain, and up to a certain point we are saving the shipping industry money.
"It is also of course by far the simplest of the regulatory options. Thanks to satellites and transponders on commercial vessels it really is quite easy to track their movements and the speed they are travelling."
Proposals to reduce the speed of ships are among the ideas that will be considered at this week's meeting of the International Maritime Organisation (IMO) in London.
Experts believe that in the medium to long term, the industry will move to alternative fuels. But there is considerable pressure, including from many countries and shipping companies, for effective short term measures to curb emissions. © Getty Images
One proposal from France would focus on oil tankers and bulk carriers but not container or cruise ships. Denmark is proposing that the industry has a goal-based standard, where it is up to the individual shipping companies as to how they meet it.
Many shipping companies are in favour of slowing down.
"Slow steaming not only reduces the fuel costs but its application does not require time-consuming procedures as it can be implemented instantly, it requires no investment from ship owners, can be easily monitored and is the most efficient means of slashing CO2 emissions," said Ioanna Procopiou, a Greek shipping company owner.
But the idea is not supported by some of the biggest names in the trade.
"Maersk remains opposed to speed limits," said Simon Christopher Bergulf, who is Regulatory Affairs Director with the giant Danish shipping conglomerate.
"We rather support the principle of applying power limitation measures. Focusing on power instead of speed limits will help deliver on the CO2 reduction targets set by the IMO, whilst rewarding the most efficient ships."
What gives campaigners hope is that shipping has already tried out the concept of going slow - back in 2008, during the global financial crisis, cargo ships slowed down to cut costs. With average speeds dropping by 12% this helped cut daily fuel consumption by 27%, which equated to a significant drop in emissions.
Campaigners believe that whatever decision the IMO eventually comes to will involve slower steaming.
"The short term measure, whatever it is, is going to reduce ship speed," said John Maggs.
"We think the best way to do this most effectively is with a direct speed limit, whether we get that or not is unknown, but ships will have to slow down in the future."