Several governments are considering a food carbon tax to tackle climate change. However, this could invertedly increase animal suffering. If consumers substitute carbon-intensive beef with meat from smaller animals (like chicken), producers will slaughter more animals to produce the same amount of meat. This is called the Small Animal Replacement Problem. This thesis develops a market model of substitution between animal products after a carbon tax and calibrates it with data for the United States. While it predicts a slight decrease in slaughtered animals, a slaughter or meat tax is a better option when society even slightly values animal welfare.