Carbon labels providing information about the carbon footprints associated with food products might influence consumer purchases, which would have a differential effect on producers throughout global food chains. We first discuss why any labels work and then describe the mechanics of carbon labels. The novelty of the paper is an examination of the issues members of the WTO have raised about all types of labels since 1995. Although carbon labels are voluntary standards for now, their increasing use could become effectively mandatory. Difficulties for exporters will include the lack of an international standard and the challenge, especially for developing country exporters, of dealing with complex carbon footprint procedures.