You're at the airline checkout, ticket nearly bought, when a tidy little box appears: Add £4.20 to offset your flight. Tick it and a small green tick appears next to your name. Conscience clear, boarding pass printed. The trouble is, the plane you're about to board burns precisely the same amount of jet fuel whether you ticked that box or not. The forest the offset paid into may or may not exist in twenty years. The maths quietly assumes a lot of things that aren't always true. None of which makes offsets useless — but it does mean the checkout-tick version of climate action is a much smaller gesture than it feels.
This is worth unpacking properly, because flying is the part of most travellers' lives where the gap between "I care about the planet" and "I am physically increasing the amount of carbon in the atmosphere" is biggest. Understanding what an offset actually does — and what it doesn't — is the first step to making smarter choices, both at the booking page and beyond it.
What a carbon offset is actually doing
An offset is, in plain terms, a financial instrument. You pay someone else to either avoid emitting carbon they would otherwise have emitted, or to remove carbon from the atmosphere — typically by planting trees, protecting forests, capturing methane from landfills, or distributing cleaner cookstoves. In return you get a certificate saying one tonne of CO₂ has been "offset" on your behalf.
The crucial word in that sentence is elsewhere. The carbon from your flight goes up into the atmosphere on the day you fly. The compensating action happens in another place, often on a different timescale, and sometimes only on paper. A well-designed offset programme genuinely results in a tonne of carbon either staying in the ground or being pulled out of the air. A poorly designed one results in a certificate and not much else.
Independent reviews of the voluntary carbon market over the past several years have repeatedly found that a meaningful share of offset projects, particularly older forest-based ones, overstate their climate benefit. That doesn't mean offsets are a scam. It means quality varies enormously and the label "carbon neutral flight" should be read with the same scepticism you'd apply to "natural" on a packet of biscuits.
The physics problem nobody on the booking page mentions
Even a perfect offset has a timing problem. The carbon from a flight enters the atmosphere immediately and starts warming the planet now. A tree that's planted to absorb that carbon takes years to mature, decades to lock away a meaningful amount, and could be lost to wildfire, drought, disease, or a future government deciding to log it.
So the equation isn't really "one tonne emitted, one tonne absorbed." It's more like "one tonne emitted today, one tonne possibly absorbed over the next forty years, assuming nothing goes wrong." For a pollutant that has its strongest warming effect in the years just after release, that's a meaningful mismatch.
Aviation makes this worse than other sectors. Burning jet fuel at altitude doesn't just produce CO₂; it produces water vapour, nitrogen oxides, and contrails that have their own warming effect — sometimes reckoned to roughly double the climate impact of the CO₂ alone. Offsets only ever address the CO₂ part. The contrail part, currently, is just there.
Why the underlying flight is what matters
The honest framing is this: an offset is a way of taking responsibility for an emission that has happened. It is not a way of preventing the emission. The plane still flies. The fuel still burns. The atmosphere still gets a slug of carbon and a smear of contrail. If the goal is fewer emissions in the air, the only thing that genuinely delivers that is fewer flights, shorter flights, fuller flights, or cleaner flights.
This is why climate scientists tend to talk about offsets as the last step in a hierarchy, not the first. The order roughly goes: avoid the emission, reduce it, replace it with something cleaner, and only then compensate for whatever's left. Skipping straight to compensation is a bit like skipping diet and exercise and going straight to liposuction. It might tidy up the visible result, but the underlying behaviour hasn't changed.
The mental-accounting trap
There's a behavioural wrinkle worth flagging too. Studies of consumer behaviour around offsets have found that the option to offset can sometimes increase the amount people fly — what researchers call "moral licensing." Once flying feels guilt-free, the marginal weekend break becomes easier to justify. The offset, intended as a brake, ends up acting as an accelerator.
You don't need a peer-reviewed study to recognise the feeling. Anyone who's ticked the box and immediately felt slightly less bad about a flight has experienced it. It's not a moral failure; it's just how human cognition deals with abstractions. A four-pound add-on at checkout is more emotionally salient than a tonne of invisible gas. The brain accepts the trade.
So how do you actually reduce a flight's emissions?
The frustrating, useful answer is that the highest-leverage decisions are made before you reach the airline website at all.
- Fly less, stay longer. One two-week trip emits roughly the same as one four-day trip if the destination is the same. The carbon is almost entirely in the take-off and landing, not in the extra nights at the destination. Longer, fewer trips is the single biggest lever most travellers have.
- Choose direct routes. Connections multiply the emissions-heavy take-off and landing phases. A non-stop flight to a single hub almost always beats a two-leg journey to the same place.
- Fly economy. Business and first class take up far more space per passenger, which means each premium seat carries a much larger share of the flight's total emissions. The same plane, the same fuel, divided across fewer people.
- Pick the train where it works. For trips under roughly six hours of rail travel, the train is usually faster door-to-door than flying once you factor in airports, and dramatically lower-carbon. Most of Europe is well served. Increasingly, parts of Asia are too.
- Pack lighter. Marginal, but real: weight is fuel. A lighter cabin is a slightly less thirsty plane.
None of these are glamorous. None of them give you a green tick at checkout. All of them outperform an offset in terms of actual atmospheric outcomes.
Where sustainable aviation fuel fits in
You'll increasingly see airlines talking about sustainable aviation fuel, or SAF — fuels made from used cooking oil, agricultural residues, municipal waste, or, eventually, synthetic e-fuels produced from green hydrogen. SAF is genuinely promising. It can drop into existing engines and, depending on the feedstock, cut lifecycle emissions substantially compared with fossil jet fuel.
The catch is volume. SAF currently makes up a tiny fraction of global aviation fuel use. Production is constrained by feedstock availability, refining capacity, and price — SAF typically costs several times more than conventional kerosene. Some airlines now offer the option to pay extra to allocate SAF to your booking, which is closer to actually cleaning up your flight than a traditional offset, because it displaces fossil fuel that would otherwise have been burned. It's still not perfect — lifecycle accounting for SAF has its own debates — but it's directionally a more honest product than a forestry credit half a world away.
How to read an offset claim without rolling your eyes
If you do choose to offset, or if you're evaluating a company's "carbon neutral" claim, a few questions cut through most of the noise:
- Who certified it? Look for standards like Gold Standard, Verra (VCS), or Climate Action Reserve. Self-certification is a red flag.
- Is it removal or avoidance? Removals (the carbon is taken out of the air and stored) are generally higher-quality than avoidance credits (something bad was prevented from happening).
- How permanent is it? A forest stores carbon for as long as the forest exists. Geological storage measures permanence in centuries. Cookstove projects don't really store anything; they reduce future emissions.
- Is it additional? Would the project have happened anyway without the offset money? If yes, you've paid for nothing.
- Is it being double-counted? Particularly important for international projects, where the host country might also be claiming the same reduction toward its own targets.
Most checkout-page offsets won't tell you any of this. That alone tells you something.
The honest place offsets belong
None of this is an argument against ever offsetting anything. High-quality carbon credits, properly sourced, do real work. Used as the last step in a serious effort to reduce emissions — not the first, not the only — they help close the gap between what we can avoid and what we can't yet. The problem is the marketing, which has spent years selling them as a substitute for the harder work, when they're really a complement to it.
The traveller who flies twice instead of four times this year, takes the train where the train works, picks economy and direct routings, and then offsets what's left with a credit they actually researched, has done meaningfully more for the climate than the traveller who flies six times and ticks every green box on the way.
That's also roughly the philosophy behind how IMPT thinks about its hotel booking platform: every booking on IMPT.io triggers a tonne of CO₂ retired on-chain, paid out of our commission rather than added to your bill — so the climate accounting happens in the background of a trip you were already taking. Pair that with smarter choices about whether and how to fly, the IMPT Shop for everyday purchases through partner brands, and the IMPT Card and Token for joining the dots between travel and the rest of your life, and the offset becomes what it should always have been: the small last piece, not the whole story.