LONDON Air travelers may be fooling themselves with a feel-good green glow from offsetting their carbon emissions, according to critics of the system.
A lack of rigor in the calculation of greenhouse gas emissions from air travel is undermining carbon offsetting as an approach to fight climate change, one expert said.
Supporters say carbon offsetting allows travelers to fight climate change without altering their behavior, by paying others to cut emissions of greenhouse gases on their behalf.
Travel company Expedia Inc on Thursday added its voice to those urging offsetting as a tool to fight climate change, allowing its customers to continue flying to exotic holiday destinations with an easier conscience.
But airlines calculate the carbon emissions from their flights differently, underlining uncertainty about the credibility of offset calculators.
The United Nation's International Civil Aviation Organization (ICAO) in June launched a carbon calculator which aimed to standardize airlines' efforts, but can still yield misleading results, according to a supplier of fuel data.
"Producing a single number is crude," said Dimitri Simos, director at Lissys Limited, supplier of an aircraft performance model previously used by the UK government and the basis for the ICAO estimate of airline emissions.
"If you go from Heathrow to Athens, ICAO gives 217 kilograms (kg) of CO2. That hides huge variations - fly in a full (Boeing) B767 and it's nearer to 160 kg per person, or fly in a half-empty (Airbus) A340 and it's more like 360 kg."
"It's the variations that are missing and that are important."
For the same trip to Athens, a carbon calculator on the British Airways website calculates CO2 emissions at 314 kg per person from London Heathrow, while Lufthansa calculates 260 kg of CO2 from London Stansted.
Carbon offsetting has also had to contend with critics who say that it only creates an illusion of fighting climate change, focusing on marginal efforts such as planting trees or building wind turbines rather than tackling the underlying problem, for example by flying less or burning less coal.
Expedia published on Thursday a survey showing that ignorance among the general public was adding to offset woes.
One in ten in the survey of 2,000 Britons thought offsetting meant walking to work instead of driving. One percent of men thought that it meant putting out a barbecue properly. Only one third understood the term.