If the mail I get from readers is any indication, the issue of climate change is a dastardly conspiracy to “redistribute global wealth,” as one memorably explained to me. Now greenhouse deniers can imagine another conspiracy: it is all a plot to get rid of fat people.

The link between obesity and climate change has come up before, although subtly. An AP story last year noted that people could combat both of these problems by walking or bicycling rather than driving (so they burn calories, not gasoline). And writing in the Huffington Post, filmmaker Bryan Young (“Killer at Large”) cited a scientist who told him that “for every pound the average American is overweight, we use an additional 938 million gallons of gasoline per year. That's enough to fill 2 million cars with gasoline every year.” It’s straightforward physics: it takes more energy to move a lot of weight than it does to move a little weight (which is also why, everything else being equal, big cars get worse gas mileage than subcompacts).

Now a paper in The Lancet today puts a scientific stamp on this. The logic goes like this: Fat people consume more food than thin people, it takes energy to grow and transport food, ergo fat people are responsible for more global warming than thin people. Or, more precisely, for 18 percent more food energy than normal people, calculate Phil Edwards and Ian Roberts of the London School of Hygiene and Tropical Medicine.

The standard definition of “overweight” is having a body mass index of 25 or greater (you can calculate yours here). A population with BMIs of 24.5 consumes, on average, 1550 calories of food per person per day just for basic metabolism and another 950 calories for daily activities. That’s 2500 calories each. A population with BMIs of 29 needs 1680 calories per person for basic metabolism, plus 1280 calories for daily activities, or 2960. That’s 18 percent more food energy.

In addition, it takes more fuel to move an obese person than a slender one, the authors note, something that “will increase further if, as is likely, the overweight people in response to their increased body mass choose to walk less and drive more.” The authors therefore advocate policies that promote walking and bicycling to reduce obesity and, hence, global warming.

But I can’t help reading in their paper the latest pretense for feeling greener-than-thou: it won’t be enough to drive a Prius, air-dry your laundry, become a vegan and ditch your air conditioning to feel smug about your tiny carbon footprint. Now you’ll have to be waif-thin, too.