Tom Otley looks at how offsetting works, and whether it mitigates the damage caused by aviation.

By now, we’ve all heard that climate change is happening. Whether we agree that it should be termed a climate emergency or not, we will also be aware that it is being caused by human activities, and those include transport and aviation. Whether it’s bush fires, floods, melting ice or the extinction of species, the planet is warming and the vulnerable are suffering as a result. So what should we do about it? 

Carbon offsetting seems to offer one answer, and is certainly one that the airlines are pushing, with Easyjet offsetting all flights since the beginning of this year, and British Airways and Air France offsetting domestic flights. There’s a catch, however, because – as with most complicated things – offsetting starts simple and quickly gets more complex.  

How it works

First, the simple bit. Offsetting is achieved by calculating the volume of emissions from a flight. For every 1kg of jet fuel burnt in the operational phase of the flight, approximately 3.15kg of carbon dioxide is released into the atmosphere. Using one of the many different online calculators, you then pay to offset these emissions. Whichever programme you use will take your money and purchase carbon credits to that amount. Carbon credits are then used by projects – typically, planting trees – that reduce the emission of greenhouse gases. 

The 3.15kg of carbon dioxide per 1kg of jet fuel quoted above is an average. Most tools now take into account the aircraft you are flying on, the distance travelled, the average wind speeds, the loading of passengers, baggage, and the cargo on the aircraft. Calculators use historic fuel consumption to derive a figure for carbon dioxide per passenger kilometre. They also take into account what class you are travelling in because the in-flight facilities provided for first class, business class and premium economy differ from those in economy in terms of weight and space, so this is factored into the calculation.  

International trade body IATA says that about 1 per cent of flyers offset their journeys, although in our own survey conducted on, some 18 per cent said they were planning to offset them. The money you pay then (eventually) goes to projects, such as planting forests, restoring peatlands, subsidising efficient stoves in Africa and helping poor communities in developing countries. It would seem, therefore, on the face of it, to be a good thing to do. But is it? 

The case against 

There are many arguments against carbon offsetting (and not all of them are made by climate change deniers). Here is a selection: 

  1. It is better to not travel at all. This is true if viewed narrowly on the question of carbon emissions, and the recent phenomenon of “flight shaming” has seen demand in a few countries slow slightly. Nevertheless, every estimate indicates that aviation is continuing to grow and so will make up a larger share of emissions as time goes on. IATA forecasts a doubling of passengers by 2036 to 8.2 billion, so no matter how much more efficient the aircraft become, that will still mean a huge increase in emissions. There’s also the small matter of businesstravellerswho are expected to fly as part of their job function. 
  2. Offsetting is a dangerous distraction; the real issue is we need to cut emissions very quickly. 
  3. Offsetting also shifts responsibility for carbon emissions from rich individuals, corporations and countries on to the poor. 
  4. Many carbon offsetting projects, such as planting trees, will take years, if not decades, to have any effect on emissions, since trees don’t reach their average carbon storage capacity until 15 to 25 years after planting. 
  5. The EU is not convinced that carbon offsetting works, and from 2021 will stop allowing offsets to count towards emissions reductions targets. This follows a report which found that 85 per cent of offset projects under the Kyoto Protocol’s Clean Development Mechanism (CDM) had failed to reduce emissions.
  6. If offsetting was effective, then the same logic would imply that paying double the offset for your flight would make it “carbon negative” so we could all fly more and more, and simply plant more and more trees.

So what should I do? 

You could cut down on your travel, if you are able. You could use video-conferencing or the phone for non-essential meetings, but assuming you do all of that and yet still fly a lot, then carbon offsetting is a way of doing something. If you decide to offset, you have a choice of calculators to work out how much to offset (see opposite). Some offer the choice of choosing what proportion of your emissions will go into an offsetting project, and what proportion will be used to buy sustainable aviation fuel (SAF). Obviously, the SAF won’t be used for your flight, but by deciding, for instance, that 80 per cent of your journey will be offset in SAF, you are effectively offsetting your flight in the present rather than the future.  

Please note, however, that while choosing to “buy” SAF is probably the most immediately sustainable way of offsetting a flight, it is much more expensive – SAF costs two or three times more than traditional aviation fuel.  

Tell me about SAF/biofuel… 

They are non-petroleum-based fuels that are blended with conventional fuels up to an industry-standard limit (currently 50 per cent, although in practice significantly less). The fuel must be resourced in a manner that avoids depletion of natural resources and mitigates its contribution to climate change. It must also meet current certification requirements for use in turbine-powered aircraft engines.  

SAF can be derived from various sources, such as cooking oil, plant oils, municipal waste, industrial off-gas, sugars and agricultural residues, and be processed in alternative ways, including thermochemical and catalytic production processes. You can read more about it on – search “Fuelling change”. One problem (and there are several) is that there won’t be enough non-food farmland to meet the demand for both the fuel we’ll need and all of the trees we need to plant. 

Shouldn’t airlines be the ones to offset? 

Some of them are doing so – British Airways, Air France, Jetblue and Delta are all offsetting a proportion of their flights (normally short-haul). However, many view this as not coming close to the true cost of the flights. 

Why are carbon offset calculators so different? 

As you can see from the box on the right, we compared a range of calculators for a nonstop return flight in premium economy between London and Hong Kong. We specified an aircraft type (B777-300ER) because both BA and Cathay Pacific, which serve the route, use that aircraft for some of the flights.  

As you’ll notice, the results vary by a lot. Dr Roger Tyers, a research fellow at the University of Southampton, explains why. “There are two parts to this. First, there are the emissions that the calculators feed into the model. There are different ways of counting these emissions. For instance, they might count only the carbon emissions, or include the non-carbon emissions as well. Do they count radiative forcing, and, if so, what multiple should you use? Some say it should be double the ground base equivalent, while some say triple, and some don’t use any because there’s no hard consensus on what it should be.  

“Then there’s the price attached to each tonne, and this depends on the offset project. Why? Because some are cheaper than others. An airline might say that its offsets are cheaper because they are buying them at scale and so are achieving economies of scale. There’s also differences in how they are accredited. Of course, you want accreditation, but there are different levels, and they come with different levels of expense, and depending on what your aim is, you’ll decide what level of accreditation is necessary for your purpose.” 

He adds: “If you are cynical, then there are sliders that airlines can move up and down in all of this until the price suits them. What they want to achieve is saying that they are offsetting a lot of carbon emissions but for a low price, so then people continue to fly with them without the price of the flights going up but at the same time thinking that the flight is offset. It’s important to realise that there are no global regulations of carbon offsetting so there is room to manoeuvre on both counting and emissions. Beware of claims that your flight will magically become carbon neutral.” 

The way forward

Most business travellers will understand the truth of this. But it returns us to the question at the start of our article. What should we do (other than change jobs)? The opinion of Andrew Murphy, who works for Transport and Environment, a European research and campaign group for clean transport, is clear: “Offsetting was invented 20 years ago out of nowhere by those who wanted to delay action on climate change. The longer we keep it going, the longer we legitimise the concept that we can continue to pollute the atmosphere.” 

So what does he suggest? “What each industry has to do is begin a tailored path to cutting its own emissions. Individuals should support and vote for politicians who are supporting action on climate change. Keeping climate at the top of the agenda is more important than buying offsets. Any money spent on carbon offsetting would be better given to charities in the developing world to help protect the vulnerable who are being affected by climate change.” 

Tyers agrees. “If the end goal is to alleviate human suffering from climate change, then I’d donate directly to disaster relief. You’d get far more for your money.”  

It’s notable that while some airlines have come late to the offsetting game, it now has gone mainstream. Nearly every major airline offers some way of offsetting. As we went to press, Finnair announced a new initiative to offer “green tickets” alongside regular ones. Details are yet to be revealed but it will offer passengers the opportunity to pay an extra surcharge on top of the ticket price at the time of booking. Finnair will match whatever surcharge the passenger is prepared to pay, and this will apply whether the passenger chooses a carbon offset programme or a proportion of the fuel to be SAF. 

For the rest of us, it is a question of whether we should trust the mechanisms of carbon offsetting while trying to reduce our travel, or instead donate directly to the relevant charities. 


How does Compensaid calculate emissions from your flight? 

“We collaborated with Myclimate to evaluate more than 43,000 individual flights to provide a detailed picture of the CO2 consumption. From small regional jets to big long-haul aircraft, we analysed the entire fleet to determine the total jet fuel consumption of a given flight from gate to gate. The objective is to record the different meteorological conditions as well as the rolling procedures on the ground and the holding patterns and detours in the air. Using this information, Myclimate developed an algorithm that calculates the corresponding CO2 emissions for each flight. The selected flight class is also taken into account and assigned a value. The algorithm is regularly updated with new flight data, most recently in 2018.”  

Why no radiative forcing? 

“Along with CO2, air traffic causes other emissions – in particular, nitrogen oxides and water vapour – which are considered to have an impact on the climate. At this time, the scientific community is still unable to conclusively determine the exact influence of these factors. This is why the CO2 calculator does not consider any other emissions apart from CO2.” 


Carbon credits 

A carbon credit is the “right” to emit one tonne of carbon or equivalent greenhouse gas. It will be generated from some verified abatement project.  

Carbon commodities 

The catch-all term for both emissions allowances and carbon offsets.  

Carbon price 

Depends on where a project is and the benefits in carbon reduction it offers. 


The Carbon Offsetting and Reduction Scheme for International Aviation, proposed and championed by ICAO (the International Civil Aviation Organisation). 

Offset certifiers 

These organisations both certify the projects, charging a fee, and then may act as a broker for the carbon emissions being offered from the projects.  

Radiative forcing 

An attempt to include the impacts of non-CO2 aircraft emissions at high altitudes. Some calculators allow you to factor this in by multiplying the carbon emissions by a recommended radiative forcing factor of 1.891, which has been set by the Department for Environment, Food and Rural Affairs. Others argue the multiplier should be higher. 

Voluntary or Verified Carbon Standard 

The VCS Standard lays out the rules and requirements that all projects must follow to be certified.