Hell hath no fury like a sheep farmer told that his favourite stew is killing the planet. There is a backlash in Wales after a World Wide Fund for Nature report placed lamb cawl top of a list of British dishes ranked by carbon footprint.

A single bowl of the traditional meat and veg affair produces 5.9 kilos of CO2 emissions, equivalent to 71 plastic bottles, 65 days of an LED lightbulb being switched on, 258 kettle boils, 31 miles in a car, or 722 smartphone charges – and way more than the other dishes the study looked at (fish and chips, chicken tikka masala and a ploughman’s).

The big problem in the cawl is, sure enough, the lamb, which the report says accounts for more than three-quarters of the dish’s impact, largely due to farting sheep (hello methane). The National Farmers’ Union Cymru said it was “astonished” at the findings, claiming the report makes unfair comparisons.

Three-bean soup. Photograph: Alamy Stock Photo

While that row simmers, what are the dishes we can eat safe in the knowledge of their baby-sized carbon footprints? The WWF study offers some general guidance, including a call for eating less meat. Lamb and beef are the worst offenders, thanks to their methane emissions and high demands on land. So more plants, and alternative sources of proteins such as peas, beans and nuts. “It’s basically about eating less processed food, less meat, and more local food,” says Tony Juniper, head of campaigns at WWF. “We’re not trying to preach but to lay out the facts and explain our choices.”

There is no definitive ranking of the dishes with the lightest footprint, but Bon Appetit, an American chain of sustainable cafes, worked with the Ecotrust charity to suggest dishes based on assessments of the impacts of their ingredients over their life cycles (including the energy used in production and transportation, as well as fertiliser use).

The results, available at the Eat Low Carbon website, are as wholesome as you might imagine. Top of the list: a three bean soup, with CO2 emissions of just 54 grams per portion. Then comes lentil soup, homemade crisps and – a rare meat appearance – grilled wild salmon (locally sourced, naturally). Falafel, steamed veg and hummus also feature. Lamb cawl, however, does not.