Could Carbon Emissions Trigger A Mass Extinction In The Ocean?

Over 90 percent of all life forms that have ever lived on this planet have perished. More than half of those disappearances have occurred during five rare, but intense geological and ecological incidents over the past 500 million years. While these mass extinctions were devastating, they created opportunities for new life in their wake. Some argue that by so rapidly altering the natural environment in ways that are changing the climate and wiping out habitats, human activity has initiated a sixth mass extinction, And, a study published lasted week suggests that increasing greenhouse gas emission rates could trigger a mass extinction in the ocean.

Using a mathematical model to predict the dynamics of the upper ocean, Dr. Daniel Rothman, a professor of geophysics at MIT, demonstrated that the carbon cycle in the ocean's shallower depths is relatively stable — even if carbon is pumped into the ocean at different rates and amounts. Scientists have assumed that changes in ocean carbon storage are related to the source of carbon dioxide. But, Rothman's findings suggest that this stability may in fact be a feature of the carbon cycle.

However, once the upper ocean has accumulated a certain amount of carbon, it will trigger a series of chemical reactions that could cause the ocean to become extremely acidic, which would feed back into this ongoing sequence of reactions, and alter the amount of carbon being stored in the planet’s oceans for millenia. In fact, once this threshold is breached, it would take tens of thousands of years for the oceans to return to their original unperturbable state.

"It’s a positive feedback,” Rothman says. “More carbon dioxide leads to more carbon dioxide. The question from a mathematical point of view is, is such a feedback enough to render the system unstable?”

This research builds off a prediction that Rothman made in 2017 – at the end of the century, our planet will reach a threshold driven by the amount of carbon dioxide in the planet’s atmosphere that could trigger Earth’s next mass extinction. According to geological records from the past 540 million years, persistent acidification, as demonstrated in Dr. Rothman's recent research, has occurred during four of the five past mass extinctions. However, these instances were due to sustained volcanism, not human activity.

The oceans are currently absorbing carbon dioxide at rates that exceed the end-Permian extinction over 250 million years ago, which is considered to be the greatest rate of carbon change in the ocean on record. Although humanity has only been pumping excessive amounts of carbon into the atmosphere for several decades, the brevity of this period could still trigger die-offs similar to ones that have occurred during previous mass extinctions.

“Once we’re over the threshold, how we got there may not matter,” says Dr. Rothman. “Once you get over it, you’re dealing with how the Earth works, and it goes on its own ride.