If marine extinction is not a reality for many species by the end of this century, scientists say, it will certainly be a strong probability.
Mass marine extinction may be inevitable. If humans go on burning fossil fuels under the notorious “business as usual” scenario, then by 2100 they will have added so much carbon to the world’s oceans that a sixth mass extinction of marine species will follow, inexorably.
And even if the 197 nations that agreed in Paris in 2015 to take steps to limit global warming in fact do so, then by 2100 humans will have added 300 billion tons of carbon to the seas. And a US scientist has calculated that the critical threshold for mass extinction stands at 310 billion tons.
So in either case, the world will be condemned to, or at imminent risk of, a “great dying” of the kind that characterised the end of the geological period called the Permian, in which 95% of marine species vanished, or the Cretaceous era that witnessed the last of the dinosaurs.
Daniel Rothman, a geophysicist at the Massachusetts Institute of Technology, reports in the journal Science Advances that he worked through hundreds of scientific studies to identify 31 occasions of significant change in 542 million years in the planet’s carbon cycle – in which plants draw down carbon from the atmosphere and cycle it through the animal community and back into the atmosphere.
For each event, including the five great mass extinctions in the geological record, he estimated the record of carbon preserved in the rocks, to find a predictable threshold at which catastrophe might be an outcome. Four of the five great extinction events lay beyond this threshold. He then considered the timescales of such extinction events to arrive at his modern-day danger zone figure of 310 billion tons.