And sure enough, Mathur found that among the nearly 800 participants she tested, those with higher levels of methane (three or more parts per million over 90 minutes) and hydrogen gases (20 or more parts per million) in their breath also tended to be heavier, with a BMI about 2.4 points greater than those with normal levels of the gases and about 6% more body fat on average.

CNN: Can you smell obesity?

Stopping the increase at 450 parts per million when the climate is generally expected to be no more than two degrees warmer than in pre-industrial times is the world's ambition.

ECONOMIST: Energy