The study, by an Oxford University team, monitored the travel patterns of nearly 500 people in Oxfordshire over a year. They excluded business travel.
They found aviation was the biggest single source of greenhouse gases emitted by the sample. It is responsible for 47.7% of emissions, followed closely by car use which is responsible for 44.7%. All other forms of transport including rail, bus, and ferries only account for 7.6% of total emissions.
These figures do not take account of the additional warming caused by aviation emissions. The Intergovernmental Panel on Climate Change has estimated that the release of emissions and water vapour high in the atmosphere results in radiative forcing between two and four times higher than aviation’s carbon dioxide emissions alone.
When the Oxford team applied a radiative forcing factor of 2.9 to the aviation emissions, it found that its share of climate impacts increased to 70.4%. Travel by car accounted for just over a quarter of emissions and all other sources combined were responsible for less than 5%.
The average climate impact from the sample was equivalent to 5.25 tonnes of CO2. But the researchers found that a few high emitters were responsible for the lion’s share.
The top 20% of emitters were responsible for over 61% of emissions and emitted an average of over 16tCO2e. The bottom 20% were responsible for less than 1% and had average emissions of just 0.2tCO2e. Most of the rest of the sample emitted between 1-3tCO2e. This pattern was the same across all modes of transport with a small number of people emitting far more than the rest of the sample.
The study found that people on higher incomes tended to have higher emissions and average emissions from high income groups were 11.2tCO2e - twice as high as the sample as a whole. The top 10% of emitters were responsible for 19.2tCO2e of emissions from their flying alone.
Conversely, lower income groups like pensioners tended to emit less than average.
The figures, particularly for car and air travel, matched well with national datasets suggesting that just a few travellers could be responsible for most of the UK’s transport emissions. This could have implications for government attempts to rein in transport emissions.
The study suggests that incremental rises in green taxes will do little to reduce car use and flying because the worst polluters will be able to absorb the modest price increases they represent.
"The doubling of the air passenger duty we saw recently won’t do anything," said Christian Brand, one of the researchers behind the report. "The only way to reduce demand [for flying] is to increase it a lot so that prices are closer to where they were in the 1980s."
He thinks that a better approach would be to target measures at high emitting groups to persuade them to change their transport behaviour.
"Individualised marketing, and providing information to households who might change their behaviour is resource-intensive, but very effective," said Dr Brand. "Projects have been running in the States for 10-15 years and have achieved a modal shift of 10-15%. In terms of carbon that’s a huge effect."
The paper also makes a strong case for personal carbon allowances as floated by Environment Secretary David Miliband last year (ENDS Report 383, p 13 ). This would not only raise awareness among high emitters, but would also benefit less well-off groups.