Our oceans may hold enough carbon in 80 years’ time to trigger a sixth mass extinction, a scientist has warned based on his mathematical prediction.
Daniel Rothman, geophysics professor at MIT, said he made the calculation based on the significant changes in the carbon cycle over the last 540 million years and everything we know so far about the previous five mass extinctions that occurred during this time.
In his paper, Rothman proposes that mass extinction occurs when one of these two thresholds are crossed – one, where changes occur at rates faster than our ecosystems can adapt in a long-timescale carbon cycle and, two, where changes are of a significantly large magnitude for carbon perturbations that take place over shorter timescales.
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.
Rothman calculated the critical amount of carbon to be about 310 gigatons, which would be enough to trigger the events that could lead to a mass wipe-out of all the major species on Earth.
But it doesn’t mean mass extinction will follow immediately. Rothman believes it will take another 10,000 years for the ecological disasters to play out but warns that by 2100, the world would be tipped into “unknown territory”.
“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.
Having previously done some work on the end-Permian extinction, Rothman identified 31 events in the last 542 million years where a significant change occurred in our planet’s carbon cycle after looking through hundreds of scientific papers.
Looking at the geochemical record, Rothman noted changes in the relative abundance of two carbon isotopes – carbon-12 and carbon-13 – for each mass extinction event.
He then created a mathematical formula based on the total mass of carbon that was added to the oceans during each event and the timescale of each event.
“It became evident that there was a characteristic rate of change that the system basically didn’t like to go past,” Rothman said.
“Then it became a question of figuring out what it meant.”
The research is published in Science Advances.