The Climate Bathtub Model

While it is true that the burning of fossil fuels currently emits more greenhouse gases than animal agriculture, it would be misleading to state that "fossil fuels are the main cause of climate change" without qualifying the statement. If the goal is to reduce emissions, then what matters is not the greenhouse gas emissions of the activity but the net reduction in emissions that would occur if that activity were to cease. If the burning of fossil fuels were to cease, then the net reduction in emissions would be approximately equal to the current emissions - pretty straightforward. But animal agriculture not only emits greenhouse gases, it also comes with an opportunity cost: it occupies a vast amount of land for grazing and production of feed crops. The end of animal agriculture would mean that much of that land would be able to regrow into forest and other natural ecosystems, which would capture a huge amount of carbon dioxide. Animal agriculture can be considered the leading cause of climate change in light of this opportunity cost, as the net reduction from ending animal agriculture would be greater than that of ending fossil fuel use.