Ryanair has emerged as an unlikely model for sustainable travel in new research showing that low-cost carriers produce up to 35 percent less carbon emissions per passenger than their full-service counterparts, due to higher load factors and seat density, as well as newer fleets.

The new research from flight-comparison website Liligo.co.uk claims that a couple flying from London to Venice and returning a week later have a carbon footprint of 410kg with Ryanair, compared to 977kg for the equivalent journey with Alitalia. A flight from London to Zurich with easyJet has a carbon footprint of 277kg per couple, compared with 688kg with Aer Lingus.

The low-cost concept also leads to higher average load factors. In 2009, the average for an easyJet flight was 86 percent and for Ryanair 82 percent. This compares with an average of 68 percent on Europe’s full-service airlines, according to the Association of European Airlines. British Airways’ flights were 73 per cent full, on average, during the same period.

An easyJet spokesman told The Telegraph: “Our policy is to expand our fleet through the acquisition of the latest-technology aircraft, as these are more fuel-efficient than older models. The average age of an aircraft in our flight is 3.5 years. We also use these aircraft as efficiently as possible, by maximising load factors and seating density.”

On an Airbus A319, the average full-service airline has 124 seats, whereas easyJet has 156.

No-frills carriers also operate from smaller “point-to-point” regional airports, which allow shorter taxi times and have fewer delays for landing slots.

Gbenga Kogbe of Liligo.co.uk told The Telegraph: “Our analysis shows that the environmental stigma of budget travel may be unwarranted. Travellers can now assess the financial and environmental costs of travelling with low-cost airlines, traditional airlines and charter-flight companies.”

The research comes as full-service airlines continue to realign towards the low-cost model. BA has cut its baggage allowance and abolished free meals on short-haul flights, whilst this week BMI announced plans to remove business class from domestic flights.