Via IFLScience (which is where science usually goes to die, but still, this is an exception):

Climate change is the greatest challenge to human health, according to the recent Lancet Commission report which calls for action to protect the global population. The report says that tackling climate change could deliver huge public health benefits, largely through phasing out coal, embracing renewable energy, and moving to a low-carbon economy. There is however one crucial issue the report fails to address: meat….

The livestock sector is a large source of global greenhouse gas emissions, with estimates of its overall contribution varying between 18% and 51%. Even in the smallest estimate, the livestock sector emits more greenhouse gas than the world’s transport networks.

According to one set of projections, by 2050 this sector will singlehandedly account for 72% of the total “safe operating space” for human-caused greenhouse gas emissions, 88% of the safe operating space for biomass use, and 300% of the safe operating space for the mobilization of nitrogen compounds in soils and elsewhere. This would lead to irreversible changes, irrespective of any efforts to mitigate climate change in other sectors of the economy.