In a new study, scientists warn that global warming may cause the greatest ocean species extinction since the Permian age (250 million years ago). Researchers estimate that as high as 90% of marine organisms died during the end-Permian Extinction.
The Great Dying, as it’s sometimes called, the worst known mass extinction event in the history of the Earth, wiped out more than half of all biological families, including more than 70 percent of land-dwelling vertebrates, leaving a clear mark in the fossil record.
The massive volcanic eruptions that lasted 2 million years may have caused this cataclysmic climate change. A 2021 study found that carbon dioxide emissions due to human activity are now twice as high than those that caused the Permian climate shift.
According to Curtis Deutsch (Princeton University geoscientist), ocean temperatures and oxygen levels are already at dangerous thresholds for certain organisms like corals and Arctic cod and could potentially pose a threat to thousands more species.
One of the reasons the researchers chose the Permian extinction as a basis for comparison was that its causes “seemed most clearly related to the kind of climate changes we are seeing now,” he said. “There were enough important similarities, the CO2-driven warming, the loss of oxygen, and the big response in the marine biosphere, that it seemed like the right comparison to start with.”
Additionally, the researchers wanted to measure their results against “the clearest, biggest magnitude of signal in the geologic record,” he said. “When you think about 90 percent of ocean species disappearing, it’s extreme.”
It’s hard to measure extinction
Human impacts, including global warming may have already led to a sixth mass extinction with an unknown scope. The first climate extinctions have occurred in the last few decades. These include the death of a tiny Australian rodent in 2019, and massive global insect and amphibian die-offs. A Nature study reported this week that 21 percent are under threat of extinction.
Uncertainty about the total number species on the planet makes it difficult to calculate the magnitude of recent die-offs in comparison to past extinctions. If the starting quantity is unknown, it’s hard to measure what’s being lost.
It is even more difficult to track ocean extinctions. The National Oceanic and Atmospheric Administration, one of the world’s top ocean research institutions, states it is impossible to know the exact number of species that live there because more than 80 percent of the oceans are unobserved and unexplored.
To overcome those challenges, Deutsch and study co-author Justin Penn, a geoscientist at Princeton University, used a decades-long database of marine animals’ tolerance of warming water and decreasing oxygen.
They then created 10 groups with similar tolerance characteristics, to create a global marine biogeography. Then they modelled how different levels or warming would affect the distribution of species, and potentially wipe them out.
They chose two very different emissions scenarios to show that today’s climate policy choices will make a big difference in the long run, Deutsch said. A high emissions path with up to 4 degrees Celsius warming by 2100 leads toward a mass extinction of ocean species that “would leave a clearly visible mark on the fossil record,” he said. The Paris Agreement’s path, which keeps ocean temperatures between 1.5 and 2 degrees Celsius could prevent the destruction of ocean biodiversity.
“We can pretty much avoid a mass extinction,” he said. “It’s not going to look like a biotic collapse in the fossil record.”
Recent research by climate scientists has raised questions about whether high-emissions scenarios are still useful. Rapid growth in renewable energy and new government- and business promises to lower emissions could keep global warming below 2 degrees Celsius by 2050, but there are no policies in place to make it happen.
Global greenhouse gas concentrations are reaching new record levels each year, and Deutsch said that, given the political and economic uncertainties highlighted by events like the invasion of Ukraine, the possibility that diplomatic efforts to curb warming could fizzle can’t be ruled out.
Malin PinskyA Rutgers evolutionary biologist and ecologist, Deutsch and Penn wrote a Perspective article on the new research. They said that global policy choices made in the last few decades have already triggered massive and rapid ocean changes such as sea level rising, ocean acidification, and global shifts in species. These are affecting food security and food security in developing nations. The last 30 years have seen more than half the human-caused CO2 emissions since 1750.
“We already know marine life is on the front lines, with species moving faster toward the poles than on land,” he said, citing the black sea dace, a fish species that has moved from offshore Virginia to offshore New Jersey in just a few decades.
“It’s part of a massive reorganization of life on earth, and this paper really does a nice job of making clear the stark choices in front of us,” he said.
Projecting long-term changes in dynamic and naturally variable ocean ecosystems for which there is very little monitoring is tough to begin with, Burrows said, and “a big problem with such projections, based on the present-day associations between species occurrence and climate (usually temperatures), is that the future climate conditions don’t exist anywhere on Earth right now.”
He stated that biodiversity has responded to climatic change of similar magnitude in past.
“By showing that their model of projected losses produces changes similar to that seen in past mass extinctions associated with similar climatic changes, the research has resulted in a more credible forecast of the upcoming extinctions due to anthropogenic climate change,” he said.
Is It Already In Progress?
Oceans have absorbed more than 90 percent of the excess heat trapped on the Earth’s surface by greenhouse gas pollution, building up at a rate equivalent to five atom bomb explosions per second. The average ocean temperature has risen to record levels almost every year, while its surface waters have become 30 percent more acidic over the past 200 years.
Hot water is already killing marine life and may have already led to the extinction of some regionally endangered species, particularly during extreme events such as marine heat waves.
There’s not enough data to know if the sixth great extinction is already underway in the oceans, but there are clear warning signs that global biodiversity is collapsing under the weight of human activities.
Scientists estimate that more than 1 billion sea creatures, including birds, died during last summer’s extreme heat wave in the Pacific Northwest. The 2003 heatwave that claimed the lives of around 70,000 Europeans also extended into the Mediterranean Sea. This caused a series if mass die-offs among different ocean species, such as rare corals. Recent global assessments have shown that 40.7 percent, 25.4 and 13.6 respectively of amphibians, and 13.6 of birds are in danger of extinction.
Elsewhere around the planet, warming seas have driven many coral reef ecosystems to the point of functional extinction. Other signs of disruption include an increase in jellyfish invasions and the rapid expansion of Sargassum seaweeds in the Caribbean. Hot water was also implicated in a mass die-off of starfish along the West Coast of North America, diminishing kelp forests and a federally designated “unusual mortality event” for gray whales lasting from 2019 into 2022.
“There is some evidence that extinctions have started ticking up already, but other human impacts are larger threats at the moment,” Pinsky said. He added that the new paper showed that global warming will soon outweigh other impacts such as habitat degradation and pollution.
“What we do know is that extirpations, local extinctions already happen,” he said. “We do have evidence from a coral reef that even short periods of low oxygen can result in permanent displacement of a species from that reef.”
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Sabine MathesiusWith the Potsdam Institute for Climate Impact Research, worked on a 2015 study showing that long-term plans to remove carbon dioxide from the atmosphere won’t do much to protect marine organisms from ocean acidification. She said that some species that are sensitive to acidification could be gone by the time large-scale atmospheric CO2 removal occurs.
“I think there are many demonstrated impacts of warming and acidification, especially the impacts of warming,” she said. “There have been these huge coral bleaching events, so that’s reason for great concern.”
Bleaching occurs when the ocean temperature becomes too high and corals are forced to expel the algae living within their tissues. This causes them to turn their color white.
Deutsch said that reducing emissions rather than removing them can lower the chance of a mass extinction.
“Species go extinct naturally all the time,” he said. “If we were to take that optimistic scenario and start reducing emissions now, it’s possible that we don’t really see a significant bump in extinction rates.”
Source: Inside Climate News