University of Connecticut geography professor Scott Stephenson said global warming will be offset by the effects of arctic shipping, but not by much.
“One thing we know very clearly is that global warming is happening in the arctic, and its actually happening at a rate that is twice that of the global average,” Stephenson said.
Stephenson and colleagues published their study on Sept. 12 in “Geophysical Research Letters”.
Stephenson said that there are two effects of shipping emissions: warming and cooling. Warming–the more obvious effect–occurs when soot from emissions lands on ice and snow, absorbing sunlight and making it melt faster.
“(Cooling occurs) through the direct scattering of sunlight through aerosols, sulfur oxides namely,” Stephenson said.
Stephenson explained that aerosols–small airborne particles emitted in ships’ exhaust–serve as “cloud nuclei” and clouds form. Those clouds then reflect sunlight back into space.
In his study, Stephenson said he and his colleagues used a climate model to forecast the warming and cooling effects of shipping emissions in the arctic.
“We’re not actually measuring any observed emissions here,” Stephenson said. “This work is future-looking.”
The predictive model uses assumptions of future arctic shipping, then estimates the fuel that would be consumed and the total emissions that would result. Stephenson said they compiled a dataset of potential future arctic emissions to use in the model.
“(The climate model is) a very sophisticated computer program that attempts to model in three dimensions all the various aspects of global climate–changes in the atmosphere, changes on land or at sea–and link these various components of the climate system together to see how they interact,” Stephenson said.
The result of the study was surprising, Stephenson said. He and his colleagues expected global warming to be a clear-cut trend, but the effect of additional ships ended up having a cooling effect of roughly 1 degree Celsius.
"This is not saying that shipping would reverse global warming,” Stephenson said.
Stephenson said the model showed warming of about ten degrees Celsius overall, but the shipping appeared to have an effect of cooling or slowing that warming.
It is important to note, Stephenson said, that experts in marine transportation expect that the international shipping sector to begin reducing the amount of sulfur in their fuels. The model in the study did not take the possibility of regulations reducing sulfur into account.
“So any cooling effect that we show could actually disappear in the future because of the change,” he said.
The next step in this work is to take regulatory changes into account in the model, Stephenson said.
Stephenson said the International Maritime Organization might impose future sulfur reduction on the global shipping industry. Another possibility the study didn’t take into account is the banning of heavy fuel, the diriest fuel currently being used. Both regulations could affect the model simulations.
“We see this work as a step towards uncovering the full picture of what shipping in the arctic might mean for the future climate,” he said.
Stephenson also said he was very concerned that some people might say, “(the study) is evidence that we should keep the heavy fuel oil to help the climate.”
“We try to be very clear that we do not endorse this (increased shipping emissions as a way to offset warming) as a strategy,” Stephenson said.
The study may have shown that shipping emissions will have a cooling factor over the course of the century, but that is not necessarily a sign that arctic shipping is a solution, Stephenson said.
“I think it’s very possible to take these findings out of context and to say, ‘Oh wow, shipping is going to solve global warming.’ No, that’s not what we mean at all,” Stephenson said.
Natalie Baliker is a campus correspondent for the Daily Campus. She can be reached via email at Natalie.Baliker@uconn.edu.