568k 
233k 
41k 
Subscribe 
Around 252 million years ago, a massive volcanic eruption spewed 100,000 billion tonnes of carbon into the atmosphere. This heated the planet and acidified the oceans, wiping out 95 percent of marine life in an extinction event that has come to be known as the Great Dying.
Now, a study published in Science Thursday is warning that the same thing could happen to the world’s oceans again if we don’t act to control the climate crisis.
“Even if the magnitude of species loss is not the same level as this, the mechanism of the species loss would be the same,” study co-author and Princeton University climate scientist Justin Penn told The Guardian.
Global warming is already putting a strain on the world’s oceans and the creatures that live there. The ocean is absorbing both heat and carbon dioxide, which reduces oxygen and causes ocean acidification. Marine heat waves are becoming more frequent and severe, killing and disrupting marine life; oxygen-depleted dead zones have increased by a factor of four since the 1960s; and shellfish like clams and mussels are already finding it harder to form shells.
The researchers set out to see how the oceans would fare in the future under different emissions scenarios. In the worst-case scenario, humans continue to burn fossil fuels and the world reaches four degrees Celsius of warming by 2100. This would cause a level of extinction by 2300 on par with the five previous mass extinction events, including the Great Dying and the asteroid that wiped out the dinosaurs, The New York Times reported.
“If we don’t act to curb emissions, that extinction is quite high. It registers on the geological scale among the major biotic collapses of diversity in the Earth’s history,” study co-author and Princeton University geosciences professor Curtis Deutsch told NBC News.
However, if warming is limited to two degrees Celsius above pre-industrial levels, then the extinction risk would fall by more than 70 percent and only four percent of ocean species would be lost.
“The future of life in the oceans rests strongly on what we decide to do with greenhouse gases today,” Penn told The Guardian. “There are two vastly different oceans we could be seeing, one devoid of a lot of life we see today, depending on what we see with CO2 emissions moving forward.”
The researchers found that life in the polar oceans faced the greatest extinction risk, but the total biological richness of ocean ecosystems was most likely to decline in the tropics.
“This paper adds to the huge body of evidence that unless more is done to curb our greenhouse gas emissions, our marine systems are on course to see a massive shift in where marine species live and, as shown in this paper, significant extinction events that could rival previous mass extinction events,” Pippa Moore, a marine science professor at Newcastle University in England who was not involved with the research, told The New York Times.