 The carbon used in the factory that makes the fertiliser to grow the straw that lines the sheds. There's the emissions from growing any food that they eat. The carbon in the fuel for the tanker that ships the feed across the ocean. The carbon in the packaging process. The fuel used to transport the chickens to slaughter. And of course the carbon footprint of any fertilisers or pesticides that may have been used. You get the picture. The carbon webs Mike calculates are mind-bogglingly complicated. How on earth do we figure out whether eating chicken can ever be good for the environment?