Diverting food waste, yard trimmings, and other biodegradable trash into a compost bin instead of a landfill can reduce emissions of the potent greenhouse gas methane. Plus, you end up with some great dirt.
The US Environmental Protection Agency says 30% of what we throw away can be composted. (You can find the EPA's list of what to compost, plus lots more information on composting, here.) When stuff that can rot gets dumped in a landfill and covered, it produces landfill gas, which is about 50% methane.
Methane is the simplest hydrocarbon. A pound of biodegradable waste can generate anywhere from 3 to 18 cubic feet of methane. If food waste were a country, it would be the third-largest emitter of greenhouse gases, behind only China and the US.
So why is it better to put waste in a compost bin rather than a landfill? Because when it's buried in a landfill, it's cut off from oxygen. Anaerobic (oxygen-hating) bacteria generate methane as they break down the waste.
A compost bin or pile exposes the waste to oxygen. Methane-creating bacteria can't live in an oxygen environment, but other bacteria love it. When those aerobic bacteria break down your vegetable peels, coffee grounds, leaves, and other compostable materials, they generate carbon dioxide.
Carbon dioxide is a greenhouse gas. But the EPA says that in terms of trapping heat in the atmosphere, methane is 28 to 36 times worse.
So compost those eggshells, grass clippings, and wads of dryer and vacuum cleaner lint. You can even do it indoors. In reducing carbon emissions, every bit helps. For an incredibly comprehensive how-to guide, check out the Gardening Mentor.