Ocean Warming Means ‘Escalating Threats’ to Marine Life through 2100
The climate in the world’s deep oceans could be changing seven times faster by mid-century, even if humanity manages a dramatic reduction in greenhouse gas emissions, according to a study published late last month in the journal Nature Climate Change.
The study “found different parts of the ocean would change at different rates as the extra heat from increasing levels of greenhouse gases moved through the vast ocean depths,” The Guardian reports. It anticipates “a rapid acceleration of climate change exposure throughout the water column” in the second half of the century, even if emissions begin falling right away.
“Our results suggest that deep sea biodiversity is likely to be at greater risk because [species] are adapted to much more stable thermal environments,” said co-author and Hokkaido University climate ecologist Jorge García Molinos. The Guardian says the study used a measure called climate velocity, the speed at which different species will have to move to find their preferred temperature range as different layers of the ocean warm.
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“At present, the world’s heating was already causing species to shift in all layers of the ocean, from the surface to more than four kilometres down, but at different speeds,” The Guardian explains. But now, “even under a highly optimistic scenario, where emissions fell sharply from now, the ocean’s mesopelagic layer—from 200 metres to one kilometre down—climate velocity would change from about six to 50 kilometres per decade by the second half of the century.” Velocity would triple at depths of 1,000 to 4,000 metres, while falling by half at the surface.
“What really concerns us is that as you move down through the ocean, climate velocity moves at different speeds,” said co-author Anthony Richardson of the University of Queensland. That reality “could create a disconnect for species that rely on organisms in different layers,” The Guardian says. “For example, Richardson said tuna live in the mesopelagic layer between 200 and 1,000 metres deep, but rely on plankton species near the surface.”
Yet because the oceans are so large, and have already absorbed so much heat that will mix from the surface into deeper waters, “marine life in the deep ocean will face escalating threats from ocean warming until the end of the century, no matter what we do now,” Richardson said.
Just as climate velocity will vary across ocean depths, he added, different species are likely to move in different directions. “This could mean that marine park areas designed to protect different species or habitats could become compromised as species moved out of the protected areas into unprotected areas,” the UK-based paper says.