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4 reasons slower ships could mean healthier oceans

Posted by Morten Thaysen - 23rd October 2018


This week, the International Maritime Organisation has the opportunity cap ship speeds globally from 2021/2022 and then gradually reduce them. This might not sound like a massive deal. But here are four reasons why reducing speeds could make a big difference for the climate and for our oceans.

  1. Lower speeds means less CO2…

Just like cars, ships emit more of everything at higher speeds (and every transport sector apart from shipping have speed limits). Capping and reducing speed could reduce shipping emissions by a third, according to Transport and Environment.

A third of what? If shipping were a country its CO2 emissions would rank it the 6th largest emitter in the world, comparable to Germany. As these emissions over the oceans are not included in the Paris Agreement’s national accounting framework – and are projected to grow by up to 250% by 2050 in line with growing global trade – unless we take action now.

  1. …and less air pollution

Slower speeds means less dirty shipping fuel being burnt, which means less particulate matter, sulfur dioxide, and nitrous oxides entering the lungs of the 40% of the world’s population that lives within 100 km of the coast.

Between 2008 and 2012 the amount of sulphur dioxide emitted annually from ships declined by 1.2 million tonnes, largely because of slower ship speeds following the financial crisis. To put this into perspective, it would take around 110 billion (yes with a “b”) passenger vehicles to emit this much sulphur dioxide annually.

  1. Slower ships could be less harmful to whales and dolphins

Underwater noise from ships is correlated with stress-related hormone levels found in whale poop, according to US researchers. Because whales and dolphins are highly dependent on echolocation, a noisy ocean is one in which their field of “vision” shrinks, affecting their ability to find prey and survive. Decreasing speed by six knots could decrease noise intensity by half.

Slower speeds also reduce incidents of “whale strike” (although I’m sure the whales would refer to it as “ship strike”. No-one knows the total number of whales being hit by ships globally, but a study in the US last year found that nearly 15% of the protected humpback whales that come every spring in the southern Gulf of Maine to feed had injuries suggesting they had been struck at least once by vessels – often open wounds in which their flesh had been chewed up by propellers.

  1. Slower speeds means more sustainable transport

At slower speeds, alternative wind propulsion for ships like sails or Flettner Rotors can take up more of the load from the engine, allowing even greater cost-savings, fuel-savings, and decarbonization.


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