The planet has experienced five mass extinction events. The worst, the Permian Mass Extinction event 252 million years ago, annihilated more than 95 percent of all life on Earth. It coincided with a significant increase in atmospheric carbon dioxide (CO2).
The Permian Mass Extinction is the perfect example of what happens when you inject too much CO2 into the atmosphere. The way in which the oceans absorbed this CO2, and subsequently acidified, was the primary kill mechanism for that event.
Disturbingly, a scientific paper published last week in the journal Science Advances, titled "Thresholds of Catastrophe in the Earth System," shows that if humans continue adding carbon to the oceans as we are on course to do, a global mass extinction event could be triggered by 2100.
Oceans as Killing Fields
The oceans are where the majority of life on Earth exists. There are more plants and animals in them than anywhere else.
The Science Advances study places the carbon threshold necessary to trigger another oceanic mass extinction event at 310 gigatons -- and notes that we are already halfway there. Worst-case predictions show that humans could add 500 gigatons of carbon to the oceans by 2100 if we continue on with business as usual.
The paper's lead author, MIT's Daniel Rothman, told Motherboard that if humanity crosses that carbon threshold, it will move the planet "to the other side of the stability boundary." He added that there won't be an apocalyptic and immediate die-off of species the moment that threshold is crossed; it might take 10,000 years for the disaster to unfold.
Every mass extinction event thus far has been marked by a major disruption of the planet's carbon cycle. Now, too, the driver of the extinction threat is increasing CO2 levels in the atmosphere. Previous mass extinction events usually saw this increase caused by volcanism. The Permian Mass Extinction, for example, was triggered when volcanism in Siberia caused magma to be introduced into peat and coal deposits which then released a massive amount of CO2 into the atmosphere and then the oceans.
Humans have already added 155 gigatons of carbon to the oceans since 1850, and could double that in just the next 83 years, or sooner. The current rate of carbon emissions is 11 gigatons released into the atmosphere annually, with 2.6 gigatons of that being absorbed into the oceans. This gives us around 80 years until we cross the threshold of triggering the next mass extinction event, according to the study.
Therefore, the pace of carbon being added to the atmosphere and ocean right now is already faster than it was during the Permian, by far the worst mass extinction event on Earth.
Meanwhile, the pH of oceans has dropped a stunning 30 percent since the Industrial Revolution began, and it is acidifying now at the fastest pace it ever has.
A 2012 study showed that oceans are acidifying faster than they have in the past 300 million years, which means they are already acidifying at higher speeds than they did during the Permian.
Another study showed that species are going extinct at a rate 1,000 times faster than the normal background rate.
"Five times in the Phanerozoic [the past 542 million years], more than three-fourths of marine animal species have vanished in mass extinctions," reads the introduction of the study. "Each of these events is associated with a significant change in Earth's carbon cycle."