Planet Earth appears to be on course for the start of a sixth mass extinction of life by about 2100 because of the amount of carbon being pumped into the atmosphere, according to a mathematical study of the five previous events in the last 540 million years.
Professor Daniel Rothman, co-director of the Massachusetts Institute of Technology’s Lorenz Centre, theorised that disturbances in the natural cycle of carbon through the atmosphere, oceans, plant and animal life played a role in mass die-offs of animals and plants.
So he studied 31 times when there had been such changes and found four out of the five previous mass extinctions took place when the disruption crossed a “threshold of catastrophic change”.
The worst mass extinction of all – the so-called Great Dying some 248 million years ago when 96 per cent of species died out – breached one of these thresholds by the greatest margin.
Based on his analysis of these mass extinctions, Professor Rothman developed a mathematical formula to help predict how much extra carbon could be added to the oceans – which absorb vast amounts from the atmosphere – before triggering a sixth one.
The answer was alarming.
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. The worst-case scenario would result in more than 500 gigatons.
Some scientists argue that the sixth mass extinction has already effectively begun. While the total number of species that have disappeared from the planet comes nowhere near the most apocalyptic events of the past, the rate of species loss is comparable.
Professor Rothman stressed that mass extinctions did not necessarily involve dramatic changes to the carbon cycle – as shown by the absence of this during the Late Devonian extinction more than 360 million years ago.
Writing in the journal Science Advances, he noted that events such as volcanic eruptions, climate change and other environmental factors could also play a role.
But he said changes to the carbon cycle – such as the burning of vast amounts of carbon in the form of oil, coal and gas laid down over millions of years – should also be considered.
“The history of the Earth system is a story of change. Some changes are gradual and benign, but others, especially those associated with catastrophic mass extinction, are relatively abrupt and…