I only think factory-farmed meat is the problem. I use "eat less meat" as a shorthand, since nearly all meat is factory-farmed meat.

Factory-farmed meat converts photosynthetic energy (grass) to food much more efficiently than free-range farming. Factory farming requires less inputs in terms of arable land and water, and emits less CO2. If everyone in the world ate non-factory farmed meat, we would have to cut down the Amazon many times over, thereby drastically reducing earth's capacity to convert CO2 back to carbohydrates.

When you decide whether your meat should be factory farmed or not, , there are consequences on two scales that are negatively correlated: Animal welfare and global warming. Which of these scales you give most weight to, will depend on your prior for anthropogenic global warming, on your beliefs about the consequences of global warming, and on the priority you give animals in your aggregation scheme over individuals with moral standing.