None of us are as good as we want to be about wasting food, and if you're like most people, that food waste ends up in your trash. This organic matter usually makes its way to a landfill where it is buried and decomposes anaerobically, which produces methane (CH4). Methane is a very potent greenhouse gas so even a little bit contributes a lot to climate change - especially in the near term.
You can get a traditional backyard composter or even a vermicomposter that uses worms to cut your carbon footprint, but there's a lot of organic material that doesn't break down well with these composting systems. That's where chickens come in! Chickens are excellent biorecyclers. Have breakfast cereal or chips that have gone stale? Chickens will take them. Left over bread and pasta can't go in a composter, but a chicken would be most appreciative. They're pretty heroic in what they can eat!
Besides reducing fuel use from transporting that food waste to a landfill and cutting methane emissions thanks to the diversion, chickens offer other co-benefits. They produce fresh eggs for you to eat - many types of chickens lay at least one egg almost every other day and that's great for your pocket book. Their manure can replace the fossil fuel-derived fertilizers you currently buy from the store and they also eat garden pests like snails and caterpillars so fewer pesticides too. A recent study suggests that chickens may also be a natural repellent to mosquitoes, which is important as our warming climate is increasing the areas where vector-borne diseases like malaria are found. Chickens are also social creatures, which means that even after they peak in egg production, they still offer all the other benefits listed above plus affection. I love my dogs and cats, but they won't eat snails and I can't use their waste to fertilize my plants.
Interested in having backyard chickens, there are lots of resources that can help you. Do try to build you coop out of left-over construction materials to save both money and further cut your carbon footprint.