It's an estimate of premature deaths based on CO2 emissions.

"Pearce and Parncutt found the peer-reviewed literature on the human mortality costs of carbon emissions converged on the "1,000-ton rule," which is an estimate that one future premature death is caused every time approximately 1,000 tons of fossil carbon are burned.

"Energy numbers like megawatts mean something to energy engineers like me, but not to most people. Similarly, when climate scientists talk about parts per million of carbon dioxide, that doesn't mean anything to most people. A few degrees of average temperature rise are not intuitive either. Body count, however, is something we all understand," said Pearce, a Western Engineering and Ivey Business School professor.

"If you take the scientific consensus of the 1,000-ton rule seriously, and run the numbers, anthropogenic global warming equates to a billion premature dead bodies over the next century. Obviously, we have to act. And we have to act fast.""