This means that if you want to reduce the environmental footprint of your diet, substituting beef and lamb with chicken and fish gets you really far. In fact, this has a much larger impact than switching from eating moderate amounts of chicken to a vegetarian or vegan diet. That’s the recommendation I give to most people. Eat less meat overall, but also replace the beef steak with chicken or tuna. In fact, it’s the diet I choose for myself: I’m a pescatarian because of the low environmental footprint of fish.

Problem solved, right? Well, not quite. This recommendation has a darker side. It’s completely at odds with animal welfare. We often ignore this fact, but it’s nonetheless true. The most environmentally-friendly meat choices mean condemning a greater number of animals to live miserable lives. There are several reasons for this.

First, low-impact meats tend to be the smallest animals. In fact, it’s the very fact that they are small that makes them so efficient. Look again at our ranking of meats by environmental impact: beef is worst; then pork; then chicken; then fish. Largest to smallest. Unfortunately, this means killing 134 chickens to get the same amount of meat you’d get from one cow.

Globally we slaughter 320 million cows for meat each year. If we sourced all of that meat from chicken instead, we’d be killing an extra 41 billion animals. But, we’d also shave off around four billion tonnes of CO2-equivalents from global emissions. That’s equivalent to the emissions of the EU and UK combined.