In a meeting in late December between U.S. President Barack Obama and Canadian Prime Minister Justin Trudeau, the two countries to take a number of steps to protect the environment in the Arctic.

The measure which got most of the attention involved a commitment to restrict drilling in the north.

Yet another aspect of the plan, which received less attention involves a strategy to phase out their use of heavy fuel oil (HFO) from vessels operating in the Arctic.

That proposal will have a direct impact on trade, as the Arctic climate warms and the use of northern routes for ocean shipping becomes more of a reality.

The Clean Arctic Alliance praised both nations for their action to rid the region of the dirtiest marine fuel.

“With ship traffic in the Arctic expected to grow dramatically as Arctic sea ice continues to decline,” said Clean Arctic Alliance advisor Sian Prior. “this announcement demonstrates real regional leadership towards protecting the Arctic from future harm.”

“We recognize that the growing possibility of an HFO spill in the Arctic, along with the significant amounts of black carbon that will be emitted by increased shipping in the region, are serious threats to the Arctic environment and climate,” said Liana James, Shipping Policy Consultant for Clean Air Task Force. “We commend the US and Canada for taking this welcome step.”

The United States and Canada have also agreed to propose a plan for the next meeting of the International Maritime Organization’s Marine Environment Protection Committee in July 2017 in order to implement the work necessary for a phase out.

A coalition of environmental NGOs has already called for phase-out of use of HFO for Arctic shipping at an IMO meeting in October 2016.

Heavy fuel oil is still used by most ocean-going commercial ships, but, due to its dangers, is already banned in Antarctica and in the waters around the Norwegian Arctic archipelago of Svalbard. Its use is still unregulated across the Arctic. The eight-nation Arctic Council has identified spills of heavy fuel oil as the top threat posed by Arctic shipping.

“HFO is the dirtiest fuel available to the shipping industry, and poses threats from spills and black carbon emissions that are too great to ignore”, said Prior. “For the sake of the marine environment and the coastal communities and wildlife that depend upon it, it is clear that Arctic shipping cannot continue relying on HFO as fuel.”

Heavy fuel oil (HFO) is a viscous, tar-like sludge that breaks down extremely slowly in cold Arctic waters and is close to impossible to clean up in the event of a spill. Currently HFO powers 44 percent of the ships currently operating in the Arctic, but it accounts for more than 75 percent of the fuel onboard Arctic ships, according to figures from the International Council on Clean Transportation.

Burning heavy fuel oil also emits significant quantities of black carbon, a highly potent short-lived climate pollutant that accelerates the already rapid pace of Arctic climate change. When black carbon falls on light-colored surfaces, such as Arctic snow and ice, it reduces the amount of sunlight reflected back into space. This process can accelerate snow and ice melt, increase the surface area of exposed, dark ocean water, and promote a self-reinforcing cycle of land and sea ice melting and climate warming.