[ad_1]
Fish of the genus Caranx, Indian Ocean, near SeychellesValery Sharifulin/TASS via ZUMA Press
This story was first published by Wired and is reproduced here as part of the Climate Desk collaboration.
A quarter ofOne billion years ago, life was not good on Earth. That’s putting it mildly. Back then the planet was in the middle of the worst mass extinction event eve—much worse than the one that wiped out the non-avian dinosaurs 66 million years ago. About 70% of land species died during the Permian Triassic extinction event. Greenhouse gases Volcanic eruptions can release these substances in Siberia poured into the skies, cooking the Earth and causing acid rain to fall back down onto the land. This mass extinction was so severe that paleontologists called it the Great Dying.
The situation was worse in the ocean. The temperatures in the tropics shot up to 10 degrees Celsius and deep-sea currents slowed down, which starved the oceans of oxygen. Only 5% of all marine species survived the Great Dying. It would take millions of years for the ocean to recover. rock bottom and return to its previous levels of diversity. TrilobitesThe entire group of underwater creatures known as the, which had been around for more than 250,000,000 years, were extinct. The land animals include the dopey-looking Lystrosaurus rapidly spread over the newly barren planet.
For oceanographers Curtis Deutsch and Justin Penn, the Great Dying can tell us a lot about where our present-day planet could be headed if we don’t get a handle on climate change.
“These environmental changes are also happening in the modern ocean today,” says Penn, a research associate at Princeton University’s Department of Geosciences and coauthor of a new paper Published in the journal Science. The oxygen content of the overall air in the Ocean has already fallen by around 2 percent since the mid-20th century. Penn and Deutsch were prompted to ask a simple question: If ocean extinctions were caused by greenhouse gas emissions in the distant past then to what extent might climate change cause them to extinctions today?
The scientists considered two possible future scenarios for determining this. In one of them, fossil fuel emissions rapidly increase—way beyond current expected trends—and lead to warming of around 4.9 degrees Celsius by 2100. The other scenario is where lower emissions limit temperature rises to just below 2 degrees Celsius by the end century. It’s worth noting that this high-emissions projection is an Unlikely worst-case scenario—it would require huge increases in coal use, even though such activity peaked in 2013. If countries stick to current policies, it’s more likely we’re headed for 2.7 degrees Celsius of warming, and if they uphold pledges made at COP26, humanity may be able to keep warming under 2 degrees Celsius.
“There is still a huge range of possible futures,” says Deutsch. “We wanted to best bracket the plausible range of futures without being overly extreme in either direction.”
These two emissions scenarios were used to estimate the ocean’s oxygen supply and demand. Like us, marine animals require oxygen to survive. However higher temperatures can reduce the amount that seawater can hold and slow down currents which would normally circulate oxygen between deep and surface ocean. Warmer temperatures also increase the amount oxygen that marine animals need to survive. This is believed to be the main reason that many marine species were extinct during the Permian–Triassic extinction.
When Deutsch and Penn ran their models to find out how species would respond in the very high- and low-emissions scenarios, they found two dramatically different visions of the planet’s future. In the very high-emissions scenario, the projected mass extinction rivals the severity of the previous “Big Five” extinctions in Earth’s past—including the Permian-Triassic extinction and the one that wiped out the dinosaurs. However, if global warming remains at the levels predicted in the low emission scenario, then the loss of species caused by climate change should remain close to current levels.
“You see us effectively sitting on the good side of a cliff,” says Douglas McCauley, a marine biologist at the University of California, Santa Barbara, who wasn’t involved in the Science paper. But over the edge of that cliff there’s the potential for mass ocean extinction, he says.
These potential future extinctions won’t happen evenly over the planet. Deutsch and Penn’s models predicted that marine species in the tropics are likely to move further north and south as oceans warm, while species already living close to the poles are at a higher risk of going extinct altogether. We’re already seeing signs of this movement in today’s oceans, says Louise Rutterford at the University of Bristol in the UK. Rutterford co-authored an analysis of marine species in the oceans that was published in 2020. She found that a species’ abundance tended to increase on the sides of its range that were closest to the poles and decrease on the side Closer to the EquatorThis suggests that warmer seas were forcing these animals away from the Equator.
Species that live near the poles are less likely than species that live further away to be able to move to as their oceans warm. That’s why in Deutsch and Penn’s model, poleward species tend to go extinct altogether while tropical species are more likely to move away from the tropics. “You’ve got this potential for this changing of the guard,” says Rutterford.
Scientists know that this movement is happening today, but it’s hard to pinpoint how bad things are at the moment. For a start, we don’t have a great sense of exactly what is happening in our oceans. Many of the best data about fish abundance come from studies on commercially important species of fish, like tuna and pollock. However, data from tropical species are much less reliable. “If you really want to find out what’s going on at the equator, we do need to have studies at the equator,” says Rutterford.
“There are quiet extinctions that are happening almost certainly in the oceans that are not being detected right now. And that wave of undetected extinction is going to become a tsunami if climate change is allowed to advance,” says McCauley.
Even if we have a better understanding of climate change, the oceans are still under extreme pressure from humans due to fishing and changes in marine habitats. The International Union for Conservation of Nature reported in 2008 that 22 percent of marine species are assessed were under threat of extinction, including 17 percent of sharks and their close relatives. One of the ways that governments and NGOs have agreed to protect the oceans is by turning vast swathes of them into marine protected areas—an oceanic equivalent to national parks.
“Marine protected areas are our best protection because in the face of the unknown they offer an ability for us to catch our breath,” says Katrina Davis, a conservation biologist at the University of Oxford. The October meeting of members of the United Nations Convention on Biological Diversity is where they will finalize their goals to protect biodiversity on the planet. One of these is The headline proposals is a plan to set aside at least 30 percent of terrestrial and marine areas as protected zones. Davis says that protecting coastal areas is especially important because it is where humans and marine species often clash.
McCauley says marine protected areas are only temporary solutions if climate change continues to escalate. “You don’t want to be trying to solve local threats to diversity and just letting climate change undo all that in the future.” A return to the Great Dying is far from inevitable, but every fraction of a degree of warming that we can halt will reduce the severity of ocean extinctions. “Our main result is that the magnitude of the future extinction depends on the CO2 emissions moving forward,” says Penn. “That story is yet to be written.”
