The barbecue season has arrived. I went to my first cookout of the year a couple of weeks ago and, while I really enjoyed a few cold beers and plenty of delicious food, I couldn’t help thinking about the smoke that came from my friend’s charcoal grill.

Does that smoke contain high levels of greenhouse gases? For insight, I contacted Eric Johnson, an environmental consultant based in Switzerland who wrote a study comparing the carbon footprints of charcoal and gas grills.

Mr . Johnson said charcoal grills typically generate three times as much greenhouse emissions than gas for the same cooking job. “People tend to overuse charcoal,” he said. “But when you use gas or propane, you turn the grill on and off.”