"Aggressive and rapid reductions in greenhouse gas emissions are critical for avoiding a major mass extinction of ocean species," says senior researcher Curtis Deutsch, professor of geosciences at Princeton University, US.

According to the research, current greenhouse gas emissions trajectories are going to heat and deoxygenate the oceans to the point where they become uninhabitable for most marine species.

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Human action, like overfishing and pollution, is often considered the worst driver of marine biodiversity loss - but the heat from climate change alone is enough to cause a massive extinction event by 2100.

According to the researchers' modelling, this event could be on par with the Permian Extinction - a loss of biodiversity that occurred 250 million years ago, and remains the worst in the Earth's history. Between 80 and 95% of the worlds species were wiped out.

"The silver lining is that the future isn't written in stone," says first author Dr Justin Penn, a postdoctoral research associate in geosciences, also at Princeton.

"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."

According to Penn and Deutsch's study, reversing greenhouse gas emissions trends diminishes the mass extinction risk by 70%.

The researchers found that as emissions increase (gray), the loss of biodiversity (red) would be greatest in tropical waters, while polar species are at the highest risk of extinction. Credit: Figure by Justin Penn

There's also bad news for reptiles. According to a different paper published this week in Nature, while they face less devastation than their marine counterparts, a fifth of the world's reptiles are threatened with extinction.

The researchers assessed 10,196 reptile species around the world, finding 1,829 (21%) to be vulnerable, endangered, or critically endangered.

Like marine species, the current obvious drivers of these threats are human activities: agriculture, logging, urban development and invasive species. Unlike marine species, the threats from climate change are more ambiguous.

The researchers say urgent conservation efforts are needed to protect these species.