Livestock emits the largest amount of greenhouse gasses out of all food sources, roughly 7.1 gigatonnes of carbon dioxide (GtCO₂) per year. This is because livestock, such as cattle, emit a large amount of methane. As a result, switching away from a meat-based diet to a plant-based diet can reduce a significant amount of greenhouse gas emissions.
Helping farmers grow more crops on the land that they already have will allow more people to be fed. This will allow less land to be turned into farmland, meaning there will be more natural habitats and fewer greenhouse gasses emitted. Livestock, however, emits the most greenhouse gas emissions, so even if more crops were grown on land, it would not decrease greenhouse gas emissions as much as eating less meat.
Reducing the price of meat will encourage more meat to be consumed and increase the demand for meat. As a result, more livestock would be raised and therefore would increase greenhouse gas emissions because there would be more animals (like cattle) to emit methane.