Climate change is mainly caused by the burning of fossil fuels (Oil, coal, natural gas). Why? because ancient sunlight caused photosynthesis in plants (like it does today), that process locks up carbon from the atmosphere and releases oxygen. As the plants (and some animals that ate the plants) dies, they were covered up by layers of rock, thus preventing the "fossils" from completely decomposing and releasing the Carbon back into the atmosphere. Millions of years this went on, storing carbon in the crust of the earth... and eventually generating the climate conditions that we have adapted to and flourished under for the last few hundred thousand years... until we came along and started digging and drilling the planet and using the ancient sunlight, stored as hydro-carbon that can burn in the presence of oxygen and create... CO2... That CO2 is like a blanket that prevents sunlight now striking the earth from being reflected harmlessly back into space. That, in turn, engages some feedback loops like melting snow and ice (Snow and Ice reflect MORE sunlight than ocean, rock, or grass).

In any event, while we could do with reducing the human and farm animal populations... these are not THE single major emitters of Co2. Methane is another issue... thus a reduction in farm animals would be good... it would also allow humans to live longer happier lives if we ate a more mixed diet. Meat was always used as a "flavoring" more than as the main ingredient in times past... even a few hundred years ago. Meat was reserved for royalty and for special occasions. There is a reason why the "Beefeaters" were a special force of guardsmen guarding the Tower of London were named "Beefeaters".

in any event, Vegans harping on non-vegans for being "fake environmentalists" is simply not the way to win the argument, in my humble opinion.