Seas May Face Most Cataclysmic Extinction in 250 Million Years – Mother Jones

KC Alfred/ZUMA Press Wire

This story was originally published by Guardian and is reproduced here as part of the climate desk Cooperation.

Global warming is new research warns it’s causing such a drastic change in the world’s oceans that it threatens a mass extinction of marine species to rival anything that has happened in Earth’s history over tens of millions of years.

Accelerating climate change is having “profound” effects on marine ecosystems, making “the risk of extinction higher and the biological richness of the sea lower than has been seen in Earth’s history over the past 10 million years,” according to the study.

The world’s seawater is constantly warming due to the extra heat generated by burning fossil fuels, while oxygen levels in the ocean are falling and the water is turning acidic by absorbing carbon dioxide from the atmosphere.

That means the oceans are becoming overheated, increasingly gasping for air — the volume of fully deoxygenated ocean water has quadrupled since the 1960s — and becoming more hostile to life. Aquatic creatures such as clams, clams and shrimp are unable to form proper shells due to seawater acidification.

All of this means the planet could be caught in a “mass extinction event rivaling those in Earth’s past,” according to the new study, published in Science. According to researchers, the pressure of the rising heat and the loss of oxygen are unpleasantly reminiscent of the mass extinction event at the end of the Permian, about 250 million years ago. Known as the “Great Dying,” this catastrophe resulted in the sinking of up to 96 percent of the planet’s marine life.

“Even if the magnitude of species loss is not at this level, the mechanism of species loss would be the same,” said Justin Penn, a climate scientist at Princeton University who co-authored the new study. “The future of life in the oceans depends heavily on what we do with greenhouse gases today. There are two very different oceans we could see, one without much life that we see today depending on what we see with future CO2 emissions.”

Truly catastrophic rates of extinction could be reached should the world emit gases that are heating the planet unchecked, leading to an average warming of more than 4C above pre-industrial times by the end of this century, the research found. This would trigger extinctions that would alter ocean life for several centuries as temperatures continue to rise.

But even in the better scenarios, the world will still lose a significant portion of its marine life. A warming of 2°C above the pre-industrial norm, projected as likely even under current climate pledges by world governments, will wipe out about 4 percent of the roughly two million species in the oceans.

According to the study, fish and marine mammals that live in polar regions are most at risk because, unlike tropical species, they cannot migrate to correspondingly cooler regions. “You’re just going to have nowhere to go,” Penn said.

The threat of climate change amplifies the other major threats facing aquatic life, such as overfishing and pollution. Between 10 and 15 percent of marine species are already at risk of extinction because of these various threats, the study, which drew on data from the International Union for Conservation of Nature, found.

John Bruno, a marine ecologist at the University of North Carolina who was not involved in the study, said the new research appears “solid,” but it differs from previous studies on the subject, which suggest species reside primarily in expand new areas instead of being completely wiped out.

“It’s very different from what most previous work has developed. But that doesn’t mean they’re wrong,” said Bruno. “I think this new work challenges some of our current assumptions about the geographic patterns of impending ocean extinctions.”

Bruno said that while extreme warming-related mass extinctions are likely in the future, the current impacts of climate change and other threats should be worrying enough for policymakers and the public.

“Personally, I’m much more concerned about the ecosystem degradation that we’re already seeing after less than 1C of warming,” he said. “We don’t have to be looking at a world that has warmed enough to wipe out humanity – we are already losing immeasurable biodiversity and ecosystem functions with the relatively modest warming of the last 50 years.”