Credit: Shuzhong Shen

In the past 540 million years, the Earth has endured five mass extinction events, each involving processes that upended the normal cycling of carbon through the atmosphere and oceans. Now Daniel Rothman, professor of geophysics in the MIT Department of Earth, Atmospheric and Planetary Sciences and co-director of MIT's Lorenz Center, has analyzed significant changes in the carbon cycle over the last 540 million years, including the five mass extinction events. Given the recent rise in carbon dioxide emissions due to human activity, he said we would reach this threshold by the year 2100 and once that happens, it could lead to an unstable environment, and ultimately, mass extinction. He thinks that given the rise of carbon dioxide over the last century, a sixth mass extinction could be on the way as estimates suggest that humans will add roughly 310 gigatons to the cycle by 2100. In this context, Rothman predicts it would take about 310 gigatonnes of carbon added to the world's oceans for us to pass the threshold – which is roughly the minimum amount expected to be contributed by the year 2100 at the rate things are going, at which point the researcher says we'll enter "unknown territory". We’re destroying all life, we have a huge problem’

“This is not saying that disaster occurs the next day,” Rothman said. "It's saying that, if left unchecked, the carbon cycle would move into a realm which would be no longer stable, and would behave in a way that would be difficult to predict. “In the geologic past, this type of behaviour is associated with mass extinction.”

The Earth has endured five mass extinction events, each involving processes that wreaked havoc on the the carbon cycle. His unique equation factored in the critical rate and magnitude of change in the carbon cycle to the timescale that separates fast from slow change from 31 events in the last 542 million years in which a significant change occurred in the carbon cycle. Following this, he devised a mathematical formula to determine the total mass of carbon added to the oceans during each event, after which “it became evident that there was a characteristic rate of change that the system basically didn't like to go past.”

Rothman estimates this to be 310 gigatons. According to Rothman, the massive amounts of CO2 emissions produced around the world are in line with previous mass extinction events in the planet’s history. "But this work points out reasons why we need to be careful, and it gives more reasons for studying the past to inform the present."
MIT physics professor Daniel Rothman's mathematical formula, published in the peer-review journal Science Advances, predicts a sixth mass extinction may be set to occur within 10,000 years if by the year 2100 current carbon dioxide emissions are not reduced, and a critical amount of carbon (310 gigatons) is added to the oceans.