Scientists at the Massachusetts Institute of Technology (MIT) have predicted that increased carbon dioxide emissions since the 19th century could trigger the feared sixth mass extinction, a widespread extermination of living species on our planet. Scientists warn that by 2100, oceans may hold enough carbon to launch mass extermination of species in future millennia.
Daniel Rothman, a professor of geophysics at the Department of Atmospheric and Planetary Sciences and co-director of the Lorenz Center at MIT, has identified “catastrophe thresholds”: a critical amount of 310 gigatonnes of carbon introduced into the oceans.
If it is exceeded, it will lead to an unstable environment and, ultimately, to mass extinction.
“This is not saying that disaster occurs the next day,” Rothman says.
“It’s saying that, if left unchecked, the carbon cycle would move into a realm which would be no longer stable, and would function in a way that would be hard to predict. In the geologic past, this type of behavior is associated with mass extinction.”
Professor Rothman has previously worked on the extinction event of the Permian, the most severe extinction in Earth’s history, in which more than 95% of marine species worldwide disappeared due to a massive increase in carbon dioxide levels.
On this occasion, he wanted to answer the question of whether current emissions of this greenhouse gas could have similar consequences today.
Soon the problem arose of comparing a geological event, which lasted for thousands or even millions of years, with a phenomenon whose duration does not reach the two centuries in which the planet has been industrialized.
To try to compare both, he devised a mathematical formula based on physical principles related to the functioning of the carbon cycle.
This natural cycle depends fundamentally on the balance between photosynthesis (the production of sugars and other molecules from carbon dioxide by plants and microbes) and respiration (the set of phenomena developed by living beings that are destined to obtain energy and produce carbon dioxide in turn).
Rothman wanted to check whether his formula worked or not, so he put it to work with historical data already collected.
Professor Rothman analyzed hundreds of geochemistry articles already published and identified 31 events in the last 542 million years in which there was a significant change in the carbon cycle of the Earth from natural causes.
Rothman measured the nature and duration of changes and associated them with the amount of CO2 that dissolved in the oceans at that time.
Soon he found a threshold common to most of the 31 events.
Almost all of them were very benign and could not destabilize the planet.
The chilling fact is that four of the five mass extinctions, which drove the carbon cycle out of control, did surpass this threshold.
In light of these data, the researcher calculated how much time it will take to reach this threshold today.
According to data from the Intergovernmental Panel on Climate Change (IPCC), this will occur by the year 2100.
As noted by MIT, The best-case scenario projects that humans will add around 300 gigatons of carbon to Earth’s oceans by the year 2100, while more than 500 gigatons will be added under the worst-case scenario, far outpacing the critical threshold. In all situations, Rothman shows that by 2100, the carbon cycle will either be close to or well beyond the threshold for catastrophe.
“There should be ways of pulling back [emissions of carbon dioxide],” Rothman says. “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.”