Fishermen around Nova Scotia should be able to maintain their present catch levels if the world abides by the Paris Agreement, according to a new study that predicts worldwide catches will drop by more than three million tonnes a year for every degree of global warming.
In research to appear today in the journal Science, experts at the University of British Columbia demonstrate with a computer model the ramifications of doing nothing to halt CO2 emissions driving the mercury ever upward, versus taking steps to limit global warming to 1.5 C above pre-industrial levels.
“We tried to quantify the implications of meeting the Paris Agreement and compare that with business as usual,” lead author William Cheung told Local Xpress.
Going along with what countries had pledged previously in terms of their carbon emissions would probably result in a world that’s 3.5 C warmer than pre-industrial levels, said Cheung, a marine biologist and associate professor at UBC’s Institute for the Oceans and Fisheries.
“We project that potential catches will decrease by more than three million tonnes per degree Celsius of warming,” the authors write.
“Species turnover is more than halved when warming is lowered from 3.5 C to 1.5 C above the pre-industrial level. Regionally, changes in maximum catch potential and species turnover vary across ecosystems, with the biggest risk-reduction in the Indo-Pacific and Arctic regions when the Paris Agreement is achieved.”
At the same time, changes in species composition will result in the disappearance of some fish now being harvested, while others move into areas where they were never seen before, Cheung said in a Skype interview from Hong Kong, where he’s visiting family for the holidays.
“So it makes it more challenging for them to do their business,” he said.
Potential catches in the Arctic will increase as the planet warms, Cheung said.
“There will be less sea ice, warmer water, so there will be more habitat for fish to go into those waters,” he said. “In fact, we’re already seeing some of that happening now.”
Fishermen are moving further north to chase Greenland halibut, Cheung said. “On the East Coast, there will be more pressure or more drivers for the fishermen to actually go further to fish in those waters.”
For the Scotian Shelf off this province and waters around Newfoundland and Labrador, Cheung’s team predicts a “moderate decrease” in fisheries catch under the scenario that sees the planet warming by 3.5 C over pre-industrial levels.
“It’s around a 10 to 20 per cent decrease, but if we were to be able to achieve the Paris Agreement of 1.5 C … the changes will basically be insignificant,” he said.
“They will be, more or less, maintaining the current level.”
The aim of the Paris Agreement is to stabilize the global temperature to within the 1.5 C mark by 2100.
Off Nova Scotia, while the catch potential should stay the same as it is now under that scenario, there will still be some changes in what’s around to be caught.
“Around 10 per cent of the species that we are seeing nowadays may change their composition,” Cheung said. “So there may be species from the southern border that are increasing on the Scotian Shelf. Or some species may be decreasing in their abundance and moving northward into the Arctic.”
He couldn’t predict whether valuable species, such as lobster, will still be crawling around the sea floor off Nova Scotia under either scenario.
Places that are closer to the equator, including the Caribbean, will see drastic changes under either situation.
“Tropical areas are more vulnerable,” Cheung said, noting those contain the hottest oceans in the world.
“Species are already living in kind of the limits of the oceans in terms of their temperature.”
Tropical areas will experience the most change in catches, no matter what plays out on the world stage, Cheung said.
“Also, the relationship is actually quite non-linear – meaning there is a sort of threshold or limit of warming above which there is a much more rapid increase in impact,” he said.
“Coincidentally, that limit is around 1.5 C to 2 C in the tropics.”
Abiding by the Paris Agreement would see “gentle” reductions on Caribbean catches by about 15 per cent, Cheung said.
“But if we were to then move away from that and get to the 3.5 C scenario, then the impacts would be more than double – so up to a 40 per cent decrease.”
And tropical fisheries that centre around coral reefs — which are particularly sensitive to ocean warming — would likely be even more vulnerable, he said.
Cheung’s team analyzed data from 19 Earth system models. They applied their model to 892 species of exploited marine fish and invertebrates. They found that a 3.5 C temperature jump will likely decrease the maximum catch potential on a global level by eight per cent compared to temperature increases of 1.5 C that will decrease maximum catch potential by 2.5 per cent.
Some regions will be hit significantly harder under the more dramatic warming condition, with the maximum catch potential decreasing by as much as 47 per cent in the Indo-Pacific region, which includes the Bay of Bengal, Gulf of Thailand, South China Sea and Sulu-Celebes Sea.
Cheung admits that he gets nightmares from predicting what changes global warming could bring to the planet’s oceans.
“But it also gives me some hope, too,” he said.
“It’s a half-full water glass thing because the world now has made this commitment on the Paris Agreement. And from our study, we demonstrated that if we would be able to keep the global temperature to what all the countries agreed to, I think the impacts on fisheries will be manageable.”
Based on the results of the new research, Cheung’s team was able to determine how much the world’s top carbon emitters have already contributed to drops in catches.
“So for example, in China in the last 10 years we calculate that, based on our study, the equivalent loss in potential catches with their emissions would be around five times the existing U.S. cod fisheries,” he said.