From the Friends of the Earth website:
"Sign-up to take part in Meat Free May now and start your journey towards reducing your environmental impact through what you eat.
Food, fundraising, and fun!
Meat and dairy production is responsible for 14.5% of all global greenhouse gas emissions and overfishing is damaging our marine ecosystems.
It would be better for ourselves and the planet if we ate less meat and fish, and a more plant based diet. To show you that it is more than possible to reduce your consumption, Young Friends of the Earth is challenging you to cut out meat and fish from your diet for an entire month.
We will support you with information and fundraising packs."
If they are concerned about the effects of dairy production, then logically they should be exhorting everyone to adopt a vegan diet.
Good luck with that one!