Check out this staggering graphic from the World Resources Institute. Global emissions from 2011 and 2012 figures show that if food loss and waste were its own country, it would be the third-largest emitter of green house gases globally!
"Global food loss and waste generate annually 4.4 GtCO 2 eq, or about 8% of total anthropogenic GHG emissions. This means that the contribution of food wastage emissions to global warming is almost equivalent (87%) to global road transport emissions." (FAO 2015)