Chardy
Sorry Callistemon that's a myth. If everyone were vegan, only a quarter of current farmland would be needed says The Economist
www.economist.com/graphic-detail/2022/01/28/if-everyone-were-vegan-only-a-quarter-of-current-farmland-would-be-needed
(I think the myth comes from rainforest bring cleared for soya production, omitting that 85% of soya production is for animal feed)
It is a very common myth. The soya being produced for animals is a huge problem. This shows the data on meat production (quite a long way down) ourworldindata.org/meat-production
For instance it takes 25kg of feed to produce 1kg of beef protein; 6.4kg to produce 1kg of pork.
You would therefore need far LESS land if more people ate only plant foods.

