A new report has warned that the new £60bn 185mph London-Manchester rail line could be less eco-friendly than the same air route over 60 years.
The report comes a few days after the UK transport secretary Lord Adonis expressed his desire to see the country's domestic air travel "progressively replaced" by a high-speed rail network.
The government-commissioned report, compiled by Booz Allen Hamilton, said that the construction and operation of a new north-south rail network will emit more CO2 than travelling by air for a 60-year period.
According to the report, commissioned by the government in 2007 but only published this year, the additional carbon emitted by building and operating a new rail route is larger than the entire quantity of carbon emitted by the air services.
The report said that the rail link will only achieve a net carbon saving if it wins a 62% market share against airlines. At present rail controls 15% of the rail/air market between London and Scotland and around 50% of the air/rail market from London to Manchester.
The report adds that the high-speed rail will also be much harder to justify if the number of trains doubles from four to eight an hour. In this scenario rail would need a market share of between 73% and 85% to achieve a net carbon saving, thanks to the increased energy use.
A spokesperson for the Department for Transport (DfT) said that the report admitted to using an overly simplistic model and had not factored in the market share rail would claim from car drivers.
Meanwhile, High Speed Two, the company set up by Lord Adonis and the DfT, will submit its own report containing an environmental study at year end.