The basic idea
A carbon offset is a payment that funds a project somewhere else which is meant to avoid, reduce or remove an amount of greenhouse gases. The buyer then claims to have balanced out some of their own emissions, for example from a flight, a business trip or running a car. Offsets are usually measured in tonnes of carbon dioxide equivalent, a way of putting different greenhouse gases on a common scale.
The reasoning is that the climate cares about the total in the atmosphere, not where each tonne comes from. That logic is sound in principle. The difficulty lies in the details: whether the project really delivers the reduction it claims, and whether it would have happened anyway.
Types of projects
Offset projects fall into a few broad groups:
- Avoiding emissions: Protecting forest that might otherwise be cleared, or replacing a polluting cooker or power source with a cleaner one.
- Reducing emissions: Capturing methane from landfill or farms, or improving energy efficiency.
- Removing carbon: Planting trees, restoring wetlands or peatland, or newer approaches such as capturing carbon from air and storing it.
Natural projects work with carbon sinks such as forests, soils and oceans, which store carbon but can also release it again. Technological removal is less dependent on land but is typically costly and still limited in scale.
Common criticisms
Offsets are widely debated, and understanding the main criticisms will help you judge any scheme.
Additionality. Would the project have happened without the offset money? If a wind farm was already going to be built, paying for its credits does not cause any extra reduction. Proving what would have happened otherwise is hard.
Permanence. Carbon stored in trees can return to the air through fire, drought, disease, pests or later logging. A tonne stored for a few decades is not the same as one kept out of the atmosphere for much longer, while fossil carbon emitted today stays in the climate system for a very long time.
Leakage. Protecting one area of forest could push logging to another, cancelling some of the benefit.
Measurement. Estimating avoided emissions requires assumptions about a baseline, and different methods can give different numbers. Some projects have been criticised for overstating their effect.
Double counting. The same reduction could be claimed by more than one party, such as a project developer, a buyer and a country, unless the accounting prevents it.
Moral hazard. Cheap offsets can make it feel acceptable to carry on emitting, delaying changes that would cut emissions at the source.
Timing. Planting trees now may take years to capture the carbon that was emitted today, so there is a time gap between cause and cancellation.
None of this means every offset is worthless. Quality varies a great deal, and it is difficult for a buyer to check without detailed knowledge.
How the schemes are checked
Some offsets are assessed against published standards, and verified by independent auditors, and records are held in registries so that each credit is retired once and not sold again. Standards differ in strictness, and a label does not guarantee a good result. Wording such as “carbon neutral” or “climate positive” has no single agreed meaning and, as with other greenwashing claims, deserves a closer look at what is actually being promised.
Questions to ask
If you are considering an offset, or a company offers you one at checkout, these questions help:
- What exactly does the money fund, and where?
- Is the project verified by an independent body, and against which standard?
- How is the climate benefit measured, and what assumptions are used?
- Would the project have gone ahead without this money?
- How long will any stored carbon be kept, and what happens if it is lost?
- How is double counting avoided, and are the credits retired?
- How much of the price actually reaches the project?
- Does the provider publish clear information, including the limits of the claim?
Clear, specific answers are a good sign. Vague answers, unexplained percentages or a lot of marketing wording are a reason for caution.
Where offsets fit with other choices
Reducing emissions at the source is generally considered more certain than paying for someone else to reduce theirs. That usually means asking first whether a journey is needed, then whether a lower-impact mode is possible, and only then thinking about offsets for what remains. This ordering applies to flying emissions in particular, since air travel is hard to avoid for some trips.
Estimating how much to offset depends on a footprint estimate, and footprint calculators vary in method and result, so numbers should be treated as approximate. Prices also vary a lot, which may reflect real differences in quality or simply different claims, and a low price is not proof of a poor project, nor a high price of a good one.
A cautious summary
Offsets are a contested tool. At best, well-run projects can deliver real benefits in addition to cutting your own emissions; at worst, they provide reassurance without much effect. If you decide to buy them, treat them as a modest extra, choose providers who are open about their methods and limits, and keep making the changes you can in your own travel. Supporting broader collective action, such as better public transport, may also do more than any individual purchase.