The population of Earth has doubled since Paul Ehrlich first warned the world that there were too many humans. Three and a half billion people later, he is more pessimistic than ever, estimating there is only a 10% chance of avoiding a collapse of global civilisation.

"Among the knowledgeable people there is no more conversation about whether the danger is real," Ehrlich told the Guardian. "Civilisations have collapsed before: the question is whether we can avoid the first time [an] entire global civilisation has given us the opportunity of having the whole mess collapse."

The idea sounds melodramatic, but Ehrlich insists his vision only builds on famine, drought, poverty and conflict, which are already prevalent around the world, and would unfold over the "next few decades".

"What it would look like is getting to the situation where more and more people are living in uncertainty about their future, subject to all kinds of disease," he said. "The really big discontinuity you can't predict is even a small nuclear war between [say] India and Pakistan.

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