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Hot years caused by climate change could wipe out thousands of tonnes of fish stocks, according to a study by the University of British Columbia.
The impact could lead to millions of job losses around the world, the researchers warn.
The damage would be on top of the damage to fish stocks caused by long-term climate change, the researchers believe.
Researchers from the UBC Institute for the Oceans and Fisheries (IOF) used computer modelling to predict how extremely hot years could affect fish catches.
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The researchers believe that if no action is taken to mitigate greenhouse gas emissions, potential catches could drop by 6%, and 77% of fish species in affected areas could drop in biomass (the amount of fish by weight in an affected area).
In Pacific Canada, sockeye salmon catches are projected to decrease by 26% on average during a high temperature event between 2000 and 2050, an annual loss of 260-520 tonnes of fish.
Combined with losses due to climate change, when a temperature extreme occurs in the 2050s the total decrease in annual catch is projected to be more than 50%.
The knock-on effects could be devastating, with almost 3 million jobs in the Indonesian fisheries-related sector projected to be lost when a high temperature extreme occurs in their waters between 2000 and 2050.
During extreme ocean temperature events and on top of projected temperature changes each decade, researchers projected that fisheries' revenues will be cut by an average of 3% globally, and employment by 2%: a potential loss of millions of jobs.
"These extreme annual temperatures will be an additional shock to an overloaded system," said lead author Dr. William Cheung, professor and director of the IOF.
"We see that in the countries where fisheries are already weakened by long-term changes, like ocean warming and deoxygenation, adding the shock of temperature extremes will exacerbate the impacts to a point that will likely exceed the capacity for these fisheries to adapt.
"It's not unlike how COVID-19 stresses the healthcare system by adding an extra burden."
Extreme temperature events are projected to occur more frequently in the future, says co-author Dr. Thomas Frölicher of the University of Bern.
“Today's marine heatwaves and their severe impacts on fisheries are bellwethers of the future as these events are generating environmental conditions that long-term global warming will not create for decades."
This year a UN climate change report warned that extreme weather events like heatwaves and droughts that previously would have happened every 50 years could soon happen every four.
That report was the first to quantify the likelihood of extreme events across a wide variety of scenarios.
It also warned that other "tipping point" events are a possibility.
Its researchers wrote: “Abrupt responses and tipping points of the climate system, such as strongly increased Antarctic ice sheet melt and forest dieback, cannot be ruled out.”
Dr Robert Rohde, lead scientist of Berkeley Earth, said: “What were once-in-50-year heat extremes are now occurring every 10 years.
“By a rise of 2C, those same extremes will occur every 3.5 years.”
The report found that (for example) once-in-a-decade heavy rain events are already 1.3 times more likely and 6.7% wetter, compared with the 50 years leading up to 1900 when human-driven warning began to occur.
Droughts that previously happened once a decade now occur every five or six years.
Xuebin Zhang, a climatologist with Environment Canada in Toronto, warned that as the world warms, such extreme weather events will not just become more frequent, but also more severe.
He also said the world should also expect more compound events, such as heatwaves and long-term droughts occurring simultaneously.
Zhang said: “We are not going to be hit just by one thing, we are going to be hit by multiple things at the same time.”
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