Composting
Food in a landfill rots without oxygen and makes methane. The same food in a compost heap rots with oxygen and makes soil. That is the entire difference.
The effect is immediate. This stops an emission that is happening right now.
Project Drawdown classifies this as Emergency Brake.
Origins
Composting is not a technology. It is what happens, and humans have been steering it for as long as they have been farming.
The Chinese were composting three thousand years ago. Roman writers described it. Every peasant farm in Europe had a muck heap, and every gardener knew that the black crumbly stuff at the bottom of it was the most valuable thing on the property. The word humus is Latin for ground, and it gives us human, which tells you what our ancestors thought we were made of.
Then, in the twentieth century, two things happened. Synthetic fertiliser made the nutrients in compost seem redundant — why turn a heap when you can buy a bag? And the sanitary landfill, one of the great public health achievements of the age, gave us somewhere to put everything else. So we stopped composting, and we started burying our food waste in an anaerobic hole in the ground.
Which turned out to be the worst possible thing to do with it.
The organic matter in a landfill is compressed, sealed, and starved of oxygen. It does not turn into soil. It ferments, slowly, for decades, and what it exhales is methane. We took the oldest recycling system on Earth and replaced it with a methane factory, and we did it for good hygienic reasons and without noticing what we had done.
What it actually is
The whole thing turns on oxygen.
Organic matter decomposing with oxygen — in a turned heap, an aerated pile, a garden bin — is broken down by aerobic microbes. They produce carbon dioxide, heat, and eventually a stable, carbon-rich material that holds water, feeds soil biology and returns nutrients to the ground.
The same organic matter decomposing without oxygen — compacted under twenty metres of other rubbish in a sealed landfill — is broken down by methanogens. They produce methane, which is roughly eighty times more potent than CO₂ over twenty years.
Same food. Same microbes, roughly. Entirely different climate outcome, decided by whether air can get in.
And the compost itself does a second job. Applied to soil, it increases organic matter, improves water-holding capacity, feeds the soil food web, and reduces the need for synthetic fertiliser — which, as the nutrient management page explains, is its own significant emissions source. A study of compost applied to California rangeland found the effects persisting for years from a single application.
It is a solution with almost no downside, and the reason it is not universal is entirely a matter of logistics: somebody has to collect the stuff separately, and somebody has to have somewhere to put it.
The numbers
The methane. Rotting food in landfill contributes up to 14% of global methane emissions. Organic waste in landfills, dumps and wastewater together account for nearly 20% of all human-caused methane.
The potency. Methane is roughly 80 times more potent than CO₂ over a twenty-year horizon. This is why diverting organics from landfill acts fast: you are shutting off a very powerful gas at the source.
The volume. Roughly a third of all food produced is wasted, and a large share of it goes to landfill. Household food waste alone exceeds a billion meals a day.
The soil. Compost adds stable organic matter, improves water-holding capacity, and reduces synthetic fertiliser demand — which cuts nitrous oxide, a gas 300 times more potent than CO₂. The carbon benefit is therefore double-counted at your peril, but it is real on both sides.
The honest limit. Composting is a diversion solution, not a prevention solution. Not producing the waste at all is far better. Composting is what you do with the waste you failed to prevent, and treating it as the primary answer lets everyone upstream off the hook.
Why it matters
There is something almost theological about a compost heap, and gardeners know it even if they would not put it that way.
You put in the peelings, the coffee grounds, the leaves, the things that are finished. You wait. And what comes out the bottom is dark and sweet-smelling and alive, and you put it back on the garden, and it grows the next thing. Nothing is wasted and nothing is lost; it simply goes around. Every farming culture that ever lasted understood this, and the ones that forgot it did not last.
What we built instead is a straight line. Grow it, ship it, eat some of it, and bury the rest in a hole where it can do nothing useful for anyone ever again, except quietly cook the atmosphere. It is not just wasteful. It is a category error about how the living world actually works.
Your grandmother had a heap at the end of the garden. She did not think of it as climate action, and it would have amused her to be told that it was. She thought of it as not being stupid with things that were still good.
She was right, and it turns out she was right about the atmosphere too, which she never mentioned, because she was busy.
What it actually takes
Separate collection, which is a municipal decision. This is the whole bottleneck. Food waste mixed into general rubbish goes to landfill and makes methane. Food waste collected separately can be composted or digested. Everything else follows from that one logistical choice, and it is made by city councils, not by individuals.
Somewhere for it to go. A separate collection with no processing facility is theatre. Municipal composting sites and anaerobic digesters have to exist, and they cost money up front.
A market for the output. Compost that nobody buys piles up. The most successful programmes connect municipal compost to nearby farms and landscapers, which closes the loop and pays part of the bill.
Contamination, which is the practical killer. Plastic in the food waste ruins the compost. Compostable plastics that do not actually compost at the facility’s temperature are a genuine and under-discussed problem. Clear rules and clear labelling matter more than enthusiasm.
And a ban, honestly. The jurisdictions that have moved fastest simply prohibited organic waste from going to landfill. It works, and it forces the infrastructure to exist.
Where it matters most
Cities, everywhere. This is one of the few solutions on this list that is fundamentally municipal. It is decided by waste contracts and collection schedules, not by farmers or forests.
South Korea is the standing proof: near-universal food waste separation, charged by weight, with recycling rates that embarrass everyone else. It is not a technological achievement. It is an administrative one.
The Mediterranean and Iberia have soils chronically low in organic matter and drying further. Compost there is not primarily a waste solution; it is a soil-survival solution.
The California coast and Western rangelands are where compost applied to grassland has been most rigorously studied, with effects on water-holding and productivity persisting for years from one application.
Rapidly urbanising Asia and Africa are where the decision is being made right now, as waste systems are being built for the first time. Building them with organics separation from the start is dramatically cheaper than retrofitting it.
How to tell it’s being done well
Is it preventing or diverting? Composting food waste is far better than landfilling it and far worse than not wasting it. A programme that leads with composting is solving the second-best problem and should say so.
Is it actually aerobic? A badly managed, unturned, compacted heap goes anaerobic and produces methane, which is the thing you were trying to avoid. Turning matters.
Where does the compost go? If it piles up unused, the loop is not closed and the programme will eventually be cut.
How is contamination handled? Plastic ruins compost. A programme with no contamination strategy will produce a product nobody wants.
What you can do
Anyone
- Compost at home if you can. A bin, a heap, a worm bin in a flat: all of them keep methane out of a landfill and put carbon back in soil.
- If your city does not collect food waste separately, that is the thing to campaign for. It is a municipal decision and it is winnable at the local level.
- Keep plastic out of it. Contamination is what kills municipal composting programmes.
Households and gardeners
- Compost is the best soil amendment available and it is free. Buying compost while sending your peelings to landfill is a small absurdity most of us commit weekly.
- Turn the heap. An unturned pile goes anaerobic and makes methane, which defeats the purpose.
Policymakers
- Ban organic waste from landfill. It is the single highest-leverage action here and several jurisdictions have proven it works.
- Separate collection is the bottleneck. Nothing else is possible without it.
- Connect municipal compost to local agriculture. It closes the loop and pays part of the cost.
Business and food service
- Restaurants and canteens produce concentrated, clean organic waste, which is the easiest possible feedstock. Most of it still goes to landfill.
- If you are building waste infrastructure in a growing city, build organics separation in from the start. Retrofitting costs many times more.
Who is working on this
We are researching which organizations in our directory of 8,493 actively work on this solution, and we only list an organization once we have verified it. That research is ongoing. In the meantime, search the directory yourself:
Questions
Why is composting better than landfilling food waste?
Oxygen. Organic matter decomposing with oxygen, in a turned heap, produces carbon dioxide, heat and stable soil-building compost. The same material compacted and sealed in a landfill decomposes without oxygen and produces methane, which is roughly 80 times more potent than CO2 over twenty years. Same food, entirely different climate outcome.
How much methane comes from food in landfills?
Rotting food in landfill contributes up to 14% of global methane emissions. Organic waste in landfills, dumps and wastewater together account for nearly 20% of all human-caused methane emissions.
Is composting really a climate solution, or just good gardening?
Both, and the climate case is stronger than most people assume. It shuts off a potent methane source at the origin, and the compost itself builds soil organic matter and reduces the need for synthetic fertiliser, which is a major source of nitrous oxide. It also acts fast, which is rare.
Isn't it better just to waste less food?
Yes, considerably, and this is the honest limit of composting. It is a diversion solution, not a prevention solution. Not producing the waste is far better than composting it. Composting is what you do with the waste you failed to prevent, and treating it as the primary answer lets everyone upstream off the hook.
What is the main obstacle?
Separate collection, which is a municipal decision rather than an individual one. Food waste mixed into general rubbish goes to landfill and makes methane. Food waste collected separately can be composted or digested. Everything else follows from that single logistical choice.
Do compostable plastics actually compost?
Often not, at least not in the facility they end up in. Many require industrial temperatures that municipal composters do not reach, and they contaminate the output when they do not break down. This is a genuine and under-discussed problem, and clear labelling matters more than good intentions.
Sources
- Project Drawdown - Deploy Composting (Drawdown Explorer) Framework and classification. Cited, not reproduced.
- UNEP Food Waste Index Report 2024
- Global Methane Assessment - UNEP and Climate and Clean Air Coalition
- Marin Carbon Project - compost application to rangeland
- US EPA - Sustainable Management of Food
The solution taxonomy follows the framework popularised by Project Drawdown. The analysis above is our own; for their carbon modeling and rankings, visit them directly.