Vox has an excellent story on annual global food waste. The climate specific stats are eye watering. 8 to 10% of carbon emissions are related to food waste and if it were a country, it would be 3rd in emissions, behind only the US and China.
Such waste takes a significant toll on the environment. The process of producing food — the raising of animals, the land and water use, and the subsequent pollution that goes with it — is horribly intensive on the planet. Food waste squanders those efforts, and then makes it worse: as it rots in landfills, it creates methane, a powerful greenhouse gas.