Passing the threshold Rothman has calculated could mean abrupt environmental change — abrupt in biological and geochemical terms meaning within 10,000 years, Rothman said.
“It’s not that the date 2100 is a magic date,” he said. “It’s that the projection of the amount of carbon that will have been added by anthropogenic means — fossil fuel burning — for the most part suggest that 300 gigaton limit will have been surpassed by end of the century. But it may happen sooner. The question in the end is: What happens next?”
The study was published Wednesday in the research journal Science Advances.
Rothman isn’t alone in warning of a potential extinction. Some scientists argue a sixth such event is under way already, with about two species a year disappearing and thousands seeing their populations and ranges shrink. And scientists have long warned that an increase in global average temperatures beyond 2 degrees Celsius (3.6 degrees Fahrenheit) could have catastrophic consequences.
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The study doesn’t necessarily identify carbon dioxide or other greenhouse gases as a culprit — but he said four of the five mass extinctions in the fossil record have been accompanied by “serious disturbances” in how carbon flows through the environment.
In Rothman’s calculations, only the strictest projections of emissions cuts would come in under the line — and with a wide range of uncertainty, that margin isn’t guaranteed. But that’s all the more reason “for trying to slow down the additional carbon in the atmosphere and oceans,” he said.
“I personally do not subscribe to a one-cause explanation for even a single mass extinction,” he said. “It’s more that many processes are at play, each of which is coupled to the other. And when they start to go in a direction that is amounting to a disturbance, one disturbance begets another, begets another one.”
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