Report: Climate-Driven Speed Limits Would Also Benefit Whales

Southern resident killer whales, Salish Sea. The endangered population is heavily affected by ship noise (file image)

Published Nov 11, 2019 4:34 PM by The Maritime Executive

A new report commissioned by the NGOs Seas at Risk and Transport & Environment suggests that a modest reduction in vessel speed would greatly reduce shipping's impact on human health, the climate and the marine environment. 

Ship speed reduction is one of the largest single interventions available for reducing fuel consumption and greenhouse gas emissions. This also saves on the cost of bunker fuel, an important consideration with IMO2020 fast approaching. The report looks at the less well-publicized benefits that speed reduction brings: a 20 percent reduction in ship speed would reduce underwater noise pollution by 66 percent, and it would cut the chance of a fatal collision between a ship and a whale by nearly 80 percent. 

Ship noise is exceptionally sensitive to speed change. Some research studies suggest that the switch to slow-steaming produced a fall-off of about two-thirds, and even more for fast-moving container ships. When a ship's propeller is turning for less than what is known as the cavitation inception speed - typically under 10 knots - underwater noise falls off even more damatically. The sound signature of ship noise overlaps substantially with the sounds used by whales for echolocation and communication. Local authorities have pursued speed reductions for underwater noise reduction and whale conservation in Vancouver, B.C. and in the Gulf of St. Lawrence (not for climate effects). 

Reduced ship speed also means large reductions in black carbon, sulfur and nitrogen oxides, all important air pollutants. SOx and NOx emissions have implications for human health, while black carbon is a concern in the Arctic due to its warming effects. 

“Speed reduction is the closest thing to a silver bullet the IMO will ever see” said John Maggs of Seas at Risk. “Delegates attending this week’s IMO climate negotiations have on the table proposals to reduce ship speed that would not just make a big dent in shipping’s climate impact but would massively reduce air pollution, underwater noise pollution, and the incidence of fatal collisions between whales and ships, all issues that the IMO must also deal with.”

The study was produced by GL Reynolds Environmental Sustainability Consultants and funded by T&E and Seas at Risk, and it is available here.