Unchecked global emissions on track to initiate mass extinction of marine life
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April 28, 2022
As greenhouse gas emissions continue to warm the world’s oceans, marine biodiversity could plummet over the next few centuries to levels not seen since the extinction of the dinosaurs, according to research from the University of Washington and from Princeton University.
Oceanographers have modeled future marine biodiversity under different projected climate scenarios. They found that if emissions are not reduced, species losses due to warming and oxygen depletion alone could reflect the substantial impact humans are already having on marine biodiversity by now. 2100 around. Tropical waters would experience the greatest loss of biodiversity, while polar species are at the highest risk of extinction, according to the April 28 study published in the journal Science.
“Aggressive and rapid reductions in greenhouse gas emissions are essential to avoid a major mass extinction of ocean species,” said lead author Curtis Deutsch, who began the research as a professor of oceanography at the ‘UW and is now at Princeton University.
The study, however, found that reversing greenhouse gas emissions now could reduce the risk of extinction by more than 70%.
“The silver lining is that the future isn’t written in stone,” said first author Justin Penn, who started the study as a graduate student at UW and is now a postdoctoral fellow at Princeton. . “The magnitude of the extinction we found is highly dependent on how much carbon dioxide we emit in the future. There is still enough time to change the trajectory of CO2 emissions and prevent the magnitude of warming that would cause this mass extinction.
Deutsch and Penn combined existing physiological data on marine species with models of climate change to predict how changes in habitat conditions will affect the survival of marine animals around the world over the next few centuries.
Water temperature and oxygen availability are two key factors that will change as the climate warms due to human activity. Warmer water is itself a risk factor for species adapted to cooler climates. Warm water also contains less oxygen than colder water and results in slower ocean circulation which reduces oxygen supply at depth. Paradoxically, metabolic rates of species increase with water temperature, so oxygen demand increases as supply decreases.
“Once the oxygen supply drops below what species need, we expect to see substantial species losses,” Penn said.
Marine animals have physiological mechanisms that allow them to cope with environmental changes, but only up to a point. Researchers have found that polar species are likely to become globally extinct if global warming occurs, as they will not have suitable habitats to move to.
Tropical marine species will likely fare better because they have characteristics that allow them to cope with the warm, low oxygen waters of the tropics. As the waters north and south of the tropics warm, these species may be able to migrate to newly adapted habitats. The equatorial ocean, however, is already so warm and oxygen-poor that further increases in temperature – and the accompanying decrease in oxygen – could render it locally uninhabitable for many species.
The researchers compared their model to past mass extinctions captured in the fossil record. They built on their previous work done at UW that connected the geographic pattern of Earth’s deadliest extinction event – the late Permian extinction around 250 million years ago – to its underlying drivers: global warming and the loss of oxygen from the oceans.
The new paper used a similar model to show that anthropogenic warming could drive extinctions from the same physiological mechanism and on a comparable scale if warming becomes large enough, Penn said.
“The latitude pattern in the fossil record reveals the fingerprints of predicted extinction due to temperature and oxygen changes,” Penn said.
The model also helps solve a permanent puzzle in the geographical pattern of marine biodiversity. Marine biodiversity increases steadily from the poles to the tropics, but decreases at the equator. This equatorial plunge has long been a mystery – researchers aren’t sure what causes it, and some have even wondered if it’s real. Deutsch and Penn’s model provides a plausible explanation for the decline in equatorial marine biodiversity – the oxygen supply is too low in these warm waters for some species to tolerate.
The big concern is that climate change will make large swaths of the ocean just as uninhabitable, Penn said. To quantify the relative importance of climate in extinctions, the authors compared future extinction risks due to global warming to data from the International Union for Conservation of Nature on current threats to various marine animals. They found that climate change currently affects 45% of marine species threatened with extinction, but is only the fifth most important stressor, after overfishing, transport, urban development and pollution.
However, Penn said, climate change may soon become the top stressor, eclipsing all others.
“Extreme warming would lead to climate-related extinctions that by the end of the century will rival all current human stressors combined,” Penn said.
The research was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration, the California Sea Grant, the California Ocean Protection Council, and the UW Climate Change Program.
Tag(s): climate change • College of the Environment • Curtis Deutsch • oceanography • School of Oceanography