Responsible travel:
Now there’s an eco-friendlier way to compare flights

The world has changed in the past few years, and travel with it. Trips have become events to look forward to with a renewed sense of wonder and appreciation. And now there’s a new way travel – one that’s gentler on the places we’ve been missing.

Next time you search for flights, try the Least CO₂ sorter. It sorts flights by their CO₂ emissions, so you get a more transparent view of your options and can make more sustainable travel decisions.

Find your next lower-emission flight now

Brits want to live more sustainably

We conducted a survey revealing that for most of us, sustainability is top of mind in our daily lives. But as travellers, we simply don’t have enough information to make sustainable decisions.

Crunching the numbers with the experts

Calculating a flight’s CO₂ is not for the faint of heart. There are so many factors that it’s next to impossible to figure out. Plus, flying also creates non-CO₂ pollutants like nitrogen oxides, ozone, soot particles, condensation trails and ice clouds that should be taken into account. That’s why we teamed up with German non-profit atmosfair, one of the world’s leading climate consulting organisations, to develop the Least CO₂ sorter.

Airline rating

An overall rating of how well an airline is performing on multiple CO₂-reducing factors.

Passenger load

Fully booked planes have more passengers, which means less CO₂ per passenger.

Cabin class

More passengers can fly in economy class seats because they take up less space, which means less CO₂ per passenger.

Aircraft type

Modern aircraft are up to 30% more fuel-efficient than older models.

Flying direct

Take-off and landing use the most jet fuel on every flight. Flying direct means you only do this once.

A clear way to fly on less CO₂

With the Least CO₂ sorter, you can immediately see how flights stack up environmentally. It shows the average amount of CO₂ and non-CO₂ emissions for all flight routes in your search result, plus how much each individual flight emits and how those compare to the average.

We’ve included more transport alternatives to our flight search engine, so in routes where trains and buses are also available, these options will appear in your search results. We also added campervan and ferry options to give you even more ways to get more places on less CO₂.

The prices and percentages shown are for illustrative purposes only.


Tips on how to travel sustainably

Choosing the right flight is just the start. As travellers, we can make choices to reduce our travel impact throughout the entire journey – from planning to transport to activities on location. Get some help with these sustainable travel tips.

Economy seats are the smallest and lightest seat option, so more of them can fit on a plane – meaning less CO₂ emissions.

Reduce plastic and save money to boot – bring your own meal in a reusable container.

Visit outdoor markets, drink locally-made beer and wine, avoid chain restaurants and buy souvenirs made in the area.

It takes energy to make every gram of weight airborne, so ask yourself if what you’re packing is really necessary.

And fill it up after you’ve passed security to stay hydrated on the plane. Practical when exploring your destination too!

Instead of jet-skiing, paragliding or four-wheeling, try alpine-skiing, snorkeling and bicycling.

Choose tours owned and operated by locals, who also have an interest in the well-being of their communities.

Before heading to the airport, unplug your electronics (especially TVs and computers) and turn down the heating and refrigerator.

No one likes hanging out on a littered beach. Clean up – especially non-biodegradable rubbish – so you can relax with a good conscience.

Avoid all-you-can-eat food buffets and ask for your leftovers “to go” – perfect for a midnight snack.

9 ways to make your flight more environmentally friendly

Dreaming of going whale-spotting in the Pacific? Go on and book that tour. Or do you fancy trekking the Brazilian rainforests? Make it happen. How about driving dune buggies in the Sahara? Let’s go!

7 ways to have a more sustainable hotel stay

What’s the biggest reason why we book hotel rooms? To get pampered, of course. Just picture those linens changed daily, the petite toiletries, the dozens of towels in every imaginable size. Time to sit back and get spoiled.

Hit the road with an eco-friendly car hire

Eco-friendly cars like hybrids and electric cars are gaining in popularity as the technology gets better and better – not to mention the style!

Now it’s your turn

Create your own eco-travel guide for your favourite destinations here.

Create a Guide

Frequently asked questions: 

CO₂ and responsible travel

In 2017, global flight traffic emitted more than 859 million tonnes of CO₂, which accounted for approx. 2% of global man-made CO₂ emissions. But flying also emits non-carbon emissions like ozone, soot particles and nitrogen oxide that, when emitted at altitudes over 9 km, account for 4% to 5% of global warming.

How much CO₂ a single plane emits depends on factors like aircraft type, distance travelled and passenger load. You can see how much your flight will emit by using our Least CO₂ sorter in your search.

Source: International Air Transport Association, Carbon Brief

Flight compensation is a way to “make up for” the CO2 emissions that were used to fly a passenger to their final destination by allowing the passenger to contribute to projects that will either remove existing CO2 from the atmosphere (e.g. planting trees) or reduce future CO2 emissions (e.g. solar farms or research into sustainable aviation fuel).

Many organisations and companies – including some airline companies – have CO2 calculators that let you calculate how much CO2 your flight has emitted and then offset your portion of those emissions. The most important thing to remember is that if you choose to offset your flight, make sure your money is helping fund a validated project. Look for projects that have e.g. the CDM Gold Standard and VCS certification labels, which means their environmental effects are closely monitored.

You can read more about flight compensation in this article.

Taking most of the common forms of transportation into account – plane, train, car, cycling and walking – it’s no surprise that biking and walking are the least CO2-intensive ways to get around. Some say that cycling actually emits less than walking because we require less food-fueled energy to go the same distance by bike than by foot, which translates into fewer CO2 emissions that went into growing, packaging and transporting the food. (If you want to dig even deeper, you can also factor in CO2 emitted from our bodies during the walk/bike ride, which would be fewer on the bike ride because, even though we may be breathing harder, we would still be breathing less overall in that distance than walking.)

Of course, it’s hard for most people to bike or walk longer distances. Between planes, trains and cars, trains emit the least CO2 by far. According to one study, a trip from London to Edinburgh emits 128 kg CO₂eq by plane, 100 kg CO₂eq by car and only 21 kg CO₂eq by train.

Say you do a flight search on KAYAK and see two good possibilities: one that emits 2,260 kg of CO₂ and one that emits 1,885 kg CO₂ (19% less). So how does this 375 kg of difference in CO₂ compare to the rest of your carbon footprint? According to this calculator, a 375 kg (19%) CO₂ reduction is the equivalent of driving a passenger car 1,500 km.

    Tell us what’s on your mind

    Do you have a great sustainable travel tip or improvement suggestions on our Least CO₂ sorter? We want to hear it. Write to us at



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    We are travellers who care about the planet

    The well-being of this planet involves us all. That’s why, just as KAYAK creates transparency on flight prices, we’re also giving you transparency on the environmental impact of flights.

    But we know there is no simple solution. We will continue to develop more eco-travel initiatives to help protect our planet for future generations.

    Start your travel planning here

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