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".
"This is not saying that disaster occurs the next day", Rothman told MIT News.
"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 hard to predict", Professor Rothman writes. According to Rothman, the massive amounts of Carbon dioxide emissions produced around the world are in line with previous mass extinction events in the planet's history. These mass extinctions involved processes that turned the normal cycling of carbon through atmosphere and oceans upside down.
In all scenarios the study found by the end of the century the carbon cycle will either be close to, or well beyond, the threshold for catastrophe.
That's mainly because it's hard to relate ancient carbon anomalies, occurring over thousands to millions of years, to today's disruptions which have taken place over little more than a century.
"It became evident that there was a characteristic rate of change that the system basically didn't like to go past", Rothman says. The other, a critical size or mass, corresponds to the total carbon added to the oceans. 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.
For the figure of 310 gigatons is just 10 gigatons above the figure expected to be emitted by 2100 under the best-case scenario forecast by the Intergovernmental Panel on Climate Change. He plotted both the mass and timescale of each event.
What Rothman's analysis doesn't mean is that everything on Earth will die immediately the day after we reach that threshold.
For the modern era, the "threshold for catastrophic change" is related to the amount of carbon present rather than its rate of increase. "Decreasing carbon emissions", Rothman says, simply.
In other words, unless humanity does something to drastically turn around our carbon situation - and there's cause for real optimism on that front, friends - we could lock in a risky extermination. The full effect of the disrupted carbon cycle could take 10,000 years to become apparent, he noted.