“It’s difficult to know how things will end up given what’s happening today. But we’re probably close to a critical threshold,” Daniel Rothman said in a recent statement from the university. “Once we’re over the threshold, how we got there may not matter. Once you get over it, you’re dealing with how the Earth works, and it goes on its own ride.”

An MIT professor who theorizes that a mass extinction could begin in the ocean by the end of the century due to climate change has more bad news: Once it begins, it could take on a life of its own.


Rothman issued a dire warning in 2017 that the oceans, if they absorb too much more carbon from human-caused carbon dioxide emissions, could undergo a mass extinction by 2100. His paper in the journal Science Advances was titled, “Thresholds of catastrophe in the Earth system .”

In his new paper, “Characteristics of an excitable carbon cycle,” published Monday in the journal Proceedings of the National Academy of Sciences, he described developing a simple mathematical model to represent the carbon cycle in the Earth’s upper ocean and how it might behave.

The carbon cycle is the process in which carbon circulates in various forms through nature. In one part of the cycle, carbon is exchanged between the ocean’s surface waters and the atmosphere, or is stored for long periods of time in the ocean depths.

Using the model, Rothman said in the study, he found that disruptions to the carbon cycle are “caused by perturbation of a permanently steady stable state beyond a threshold.”

“This paper suggests . . . that the magnitude of many disruptions is determined not by the strength of external stressors but rather by the carbon cycle’s intrinsic dynamics,” he wrote.


In the university statement, Rothman said, “When you go past a threshold, you get a free kick from the system responding by itself.”

He also warned in the study that the effect of the unprecedented injection of carbon into the ocean currently being caused by humans spewing carbon dioxide into the atmosphere could be similar to that of the injection at a lower rate over a much longer period of time caused by massive volcanic activity millions of years ago.

“The unusually strong but geologically brief duration of modern anthropogenic oceanic CO2 uptake is roughly equivalent, in terms of its potential to excite a major disruption, to relatively weak but longer-lived perturbations associated with massive volcanism in the geologic past,” Rothman wrote.

Changes in the amount of carbon stored by the ocean have happened periodically over Earth’s history. Most disruptions have been relatively benign, but all previous mass extinction events have been accompanied by such disruptions, the study said.

The rising levels of carbon dioxide in the atmosphere since the Industrial Revolution are causing climate change, with effects including global warming, severe weather, and rising seas. But the rising carbon is also having an impact in the oceans, which absorb about 30 percent of the carbon dioxide released in the atmosophere, according to the National Oceanic and Atmospheric Administration.

The extra carbon dioxide is causing the ocean to become more acidic, harming the ability of marine organisms to build their shells and skeletons.


Rothman’s model incorporated a feedback mechanism that researchers have said happens when those organisms decline — which leads to even more extreme ocean acidification.

The study, which he called a work of “exploratory theory” and a “first attempt,” suggests that, once the threshold has been reached, “the effects could be larger and longer-lasting than people think,” Rothman said in a telephone interview.

“The emissions trajectory that we’re on appears to be bringing us to a level that’s consistent with past thresholds. What happens after that is unclear,” he said.

The takeaway?

“We should limit carbon dioxide emissions,” said Rothman. “The carbon cycle is a nonlinear system, and if you perturb it, surprising things may happen.”

Jeremiah Manion of the Globe staff contributed to this report.