In case there weren’t already enough reasons to limit global warming to less than 1.5 degrees Celsius, a new study released in Nature reveals that even a 1 degree increase in ocean temperatures leads to a significant increase in mercury exposure among fish — and the people that consume them.

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The joint study was published by Harvard’s School of Public Health and School of Engineering and Applied Sciences and used a variety of simulation models to examine and predict how environmental factors affect the levels of mercury in cod and dogfish. Their models use historical data, as far back as 1970, when cod had approximately 6 to 20 percent less mercury in their diets. Yet researchers also found that dogfish had 33 to 61 percent higher mercury in their diets in 1970, because overfishing at the time led them to eat squid that are high in mercury.

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In the last four decades, policies that regulate and limit mercury emissions have made a dent in mercury exposure, but the researchers concluded that rising ocean temperatures are reversing this progress.

“This research is a major advance in understanding how and why ocean predators, such as tuna and swordfish, are accumulating mercury,” said Elsie Sunderland, senior author and a Harvard professor in environmental chemistry.

According to the researchers, unusually warmer water makes it harder for fish to breathe and swim; therefore, it forces fish to consume more energy. The more they eat, the higher their levels of mercury exposure are. Warmer temperatures might also alter the availability of their preferred diet, forcing fish like the dogfish to eat high-mercury options such as squid.

For every 1 degree the ocean warms, dogfish are exposed to 70 percent more mercury. Cod, which also live in the researchers’ study area off the coast of Maine, are exposed to approximately 32 percent more mercury for every single degree the ocean warms.

“Climate change is going to exacerbate human exposure to methylmercury through seafood,” Sunderland said. “So to protect ecosystems and human health, we need to regulate both mercury emissions and greenhouse gases.”

+ Nature

Via Harvard Gazette

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