Marine life around the planet is threatened — and in some instances, on track toward extinction — if greenhouse gas emissions are left unchecked.
That’s according to a study published in the April 2022 issue of the peer-reviewed journal, Science. Within a century, they say the impacts of human-driven climate change on marine biodiversity could be comparable to all anthropogenic stressors on oceanic life to date. If emissions maintain the track they are currently on and the ocean continues to warm, biodiversity may plummet in the next few centuries, possibly creating an extinction event like the one that killed the dinosaurs.
Unless global leaders do something about emissions.
“Aggressive and rapid reductions in greenhouse gas emissions are critical for avoiding a major mass extinction of ocean species,” said senior study author Curtis Deutsch, professor of geosciences and the High Meadows Environmental Institute at Princeton, in a news release.
To come to these findings, research at Princeton University built on previous data published in 2018 and conducted at the University of Washington. They turned to what is known as the “Big 5” mass extinction events of Earth’s history, all of which coincided with global environmental changes. The largest occurred more than 250 million years ago before dinosaurs inhabited the planet. During this so-called “Great Dying,” plants and animals were “mostly obliterated” after a series of volcanic eruptions in Siberia. By analyzing fossil records, the team determined that 81% of marine species were killed during this time, essentially reversing millions of years of evolution.
Under their theory, the researchers propose that those volcanic eruptions caused oceanic warming akin to those associated with climate change today.
Greenhouse gas emissions warm oceans by trapping more energy from the sun, forcing oceans to absorb more heat. In turn, this decreases the supply of oxygen held within their waters. This increases the metabolic demand of marine animals — if they must work harder for their food in warmer conditions that they may not be well-adapted for, they require more oxygen. (Think of it as trying to catch your breath while jogging on a hot, summer day versus a cooler, fall afternoon.)
Estimating marine biodiversity losses is difficult, as most ocean waters are deep, remote, and otherwise inaccessible. In fact, scientists have better maps of Mars than they do of Earth’s oceans. That’s why it is hard to quantify the impact of climate change on species both known and unknown to science. According to figures published by the International Union for Conservation of Nature, climate change affects 45% of marine species at risk of extinction — only the fifth most important stressor after overfishing, transportation, urban development, and pollution
To see how many species will be lost based on habitat loss from climate change, the scientists compared extinction risk from future climate change with current anthropogenic threats by modeling various projections of greenhouse gas emissions and how levels would change marine habitats. They found similar patterns between the 2018 research depicting life 252 million years ago and the world now — as ocean temperatures increase, oxygen decreases, making it harder for marine life to survive.
Climate change could soon overpower other stressors impacting marine animals, which include overfishing and urbanization. Marine animals can cope with environmental changes, but only to a certain point. If climate warming continues, some species may simply not have other habitats to go to.
Some tropical species may see their ranges expand as water temperatures get warmer, but the equatorial ocean is already so warm and low in oxygen that the region may become inhabitable. On the other hand, polar species were dubbed to be at the highest risk of extinction. This is in part due to polar regions already having low oxygen levels yet remaining some of the most productive waters on the planet.
Interestingly, the research also helps to explain a phenomenon whereby marine biodiversity increases the further one gets from the poles, but then drops off along the equator — now, the team suggests it could be because the waters are too warm and the oxygen levels too low to support all but a select number of specially adapted species
But hope is not lost, concluded the researchers. Limiting warming to 2 degrees Celsius would cut severity of extinctions by more than 70%, avoiding mass marine extinction.
“The silver lining is that the future isn’t written in stone,” said study author Justin Penn, a postdoctoral research associate in the Department of Geosciences. “The extinction magnitude that we found depends strongly on how much carbon dioxide [CO2] we emit moving forward. There’s still enough time to change the trajectory of CO2 emissions and prevent the magnitude of warming that would cause this mass extinction.”
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