The gap between the carbon footprints of the highest and lowest-income people is growing wider, despite carbon dioxide emissions falling overall in some countries.

“From an ethical perspective, if those that are already better off get a larger share of a limited resource [CO2 emissions], then that’s clearly unfair,” says Edgar Hertwich at the Norwegian University of Science and Technology.

It is no surprise that richer people consume more, and so generally have larger carbon footprints. “The wealthier you get, the …