People should give up eating meat to save the planet. That's the advice from a leading expert on climate change.
Cows and pigs produce a large amount of a greenhouse gas called methane, which is thought to cause global warming.
The animals also need places to live, which can lead to forests being cut down to make room for them, and to grow food for them to eat.
Climate chief Lord Stern told the Times newspaper that "a vegetarian diet is better."
He reckons eating meat "puts enormous pressure on the world's resources".
But farmers disagree. A group called the National Farmers Union says: "Going vegetarian is not a worldwide solution."
There is a big meeting of world experts in Denmark in December to try to come up with a deal that might reduce greenhouse gases and tackle climate change.