In the new study, scientists studied mitochondrial DNA extracted from well-dated fossil bear skeletons to work out how population size changed over time.

BBC: Early human 'squatters' drove cave bears to extinction

But unlike finite fossil fuels, this resource continues to grow, driven by increasing GDP, population, and service loads.

FORBES: Log Baby Log: The Race to The Big New Resource Play You Haven't Heard Of

In the years since, the population has grown from 3 billion to 7 billion and consumption of fossil fuels has only accelerated.

FORBES: Meditation On A Shrinking Planet

Rampant population growth and changes to the environment caused by humans, including the burning of fossil fuels and the conversion of nearly 43% of the planet's land to farms or cities, threaten to cause an abrupt and unpredictable shift in the global ecosystem, 22 scientists from five countries said in their paper.

CNN: STORY HIGHLIGHTS