Why is food waste considered a major environmental problem?

Because the emissions are not primarily from the food rotting, they are from everything that went into producing it. Land cleared, water used, fertiliser manufactured and applied, fuel burned in farming, processing, refrigeration and transport. When food is discarded, all of that was spent for nothing, and roughly a third of food produced globally is never eaten.

That makes food waste a large share of total emissions, comparable to entire industrial sectors, and it is unusual among environmental problems in that reducing it requires no new technology.

The disposal stage adds a second effect. Food sent to landfill decomposes without oxygen, producing methane, which traps far more heat than carbon dioxide over short timescales. Food waste collected separately and composted or digested anaerobically in a controlled facility avoids this, and the digestion route can capture the methane as usable gas.

Where waste occurs differs by region. In lower income countries losses concentrate earlier in the chain, through inadequate storage and transport. In higher income countries the majority occurs in households and retail, which is why consumer behaviour matters more here.

The household reductions that make the most difference are unglamorous: planning purchases, storing food correctly, and understanding date labels. Use-by dates concern safety and should be respected. Best-before dates concern quality, and a great deal of edible food is discarded because the two are conflated.

Freezing is underused as a pause button, and most foods freeze better than people assume, including bread, milk, cheese and cooked leftovers.

One structural contributor is worth naming: cosmetic standards. Produce rejected for size or appearance never reaches sale despite being perfectly edible, and that loss happens before any consumer has the chance to waste it.