SEATTLE, Wash. — Marine biodiversity could plummet to levels not seen since the extinction of the dinosaurs because of climate change, a new study warns. A team from the University of Washington say speedy and aggressive reductions in greenhouse gas emissions in the next few years are necessary to avoid a mass extinction of plants and animals over the next few centuries.
Their study finds tropical waters would see the biggest loss of biodiversity while polar species are at the greatest risk of extinction. If rising emissions remain unchecked, the loss of sea species from warming ocean temps and oxygen depletion alone could devastate marine biodiversity by the year 2100.
The team estimates that reducing greenhouse gas emissions could slash the risk of extinction by more than 70 percent.
“Aggressive and rapid reductions in greenhouse gas emissions are critical for avoiding a major mass extinction of ocean species,” says study senior author Curtis Deutsch in a university release.
Learning from past mass extinctions
For the study, Washington and Princeton University researchers combined existing data on marine species with climate change models to help them predict how changes to habitats will affect the survival of sea animals around the world over the next few centuries. They compared their model to the magnitude of past mass extinctions.
Their work built on studies linking the geographic pattern of the End-Permian extinction 250 million years ago to climate warming and ocean loss from the seas. That extinction event was even deadlier than the end of the dinosaurs and killed off 81 percent of underwater species. Researchers found patterns that were in place before the deadliest mass extinctions are also in place now.
Water temperature and oxygen availability are the two main things that will change as human activity drives up global temperatures. Warmer water is dangerous for species that cannot adapt to it. These waters also hold less oxygen than colder water, causing a more sluggish ocean circulation that cuts oxygen supply in deep water.
Species also have faster metabolisms in warmer water, so the demand for oxygen rises even as the supply falls. Sea animals can often adapt to environmental changes, but only up to a certain point. Polar species are also more likely to go extinct if global warming keeps on going because they will have no suitable habitats to move to.
Meanwhile, tropical marine species are likely to do better because they have traits that allow them to cope with warm, tropical water, which is low in oxygen. As waters north and south of the tropics warm, these species may be able to move to new, suitable habitats.
Earth’s uninhabitable zone may get much bigger
The equatorial ocean is already so warm and low in oxygen that further increases in temperature, and a resulting decrease in oxygen levels, may make it uninhabitable for many species. The pattern of extinction the team’s model projected which will see more species go extinct at the poles than the tropics, mirroring the pattern of past mass extinctions.
Earlier research has shown temperature-dependent increases in oxygen demand, paired with decreases in oxygen availability due to volcanic eruptions, can explain the geographic patterns of species loss during the End-Permian Extinction ago.
For the new study, researchers used a similar model to show warming could drive extinctions at a similar scale if warming continues globally in the 21st century. The model also helps explain why marine biodiversity increases steadily from the poles to the tropics before dropping off suddenly at the equator.
This has long been a mystery, but the researchers say it is because the oxygen supply is too low in these warm waters for some species to tolerate. Scientists’ main concern is that climate change will make vast swathes of the ocean similarly uninhabitable over the next few decades.
“Extreme warming would lead to climate-driven extinctions that, near the end of the century, will rival all current human stressors combined,” says Justin Penn, the study’s first author.
There are still bigger threats to modern day marine life
To quantify how important climate change was in driving extinctions, the team compared the risks from climate warming to data from the International Union for the Conservation of Nature on threats to various marine animals. Currently climate change is only the fifth-largest risk to species behind overfishing, transportation, urban development, and pollution. However, global warming could soon become a greater danger to species than all of these factors.
“The silver lining is that the future isn’t written in stone,” Penn adds. “The extinction magnitude that we found depends strongly on how much carbon dioxide 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.”
The findings are published in the journal Science.
South West News Service writer Gwyn Wright contributed to this report.