Government plans to cut emissions of greenhouse gases by 60% by 2050 will be "impossible" if the huge airport expansion forecast by the Department for Transport goes ahead, a senior adviser on green issues warned today.

Sir Jonathon Porritt, chairman of the Sustainable Development Commission, issued the blunt warning in a report calling for urgent action by the department to deal with climate change caused by aircraft emissions.

He said there was a conflict between the department's Air Transport white paper, published last December, and the government's strategic commitment to dealing with the problem.

The SDC's report urges the government to safeguard its pledges on sustainable development and climate change.

Greenhouse gases, the main cause of climate change, are increasing due to the boom in air travel, and the growth of low-cost airlines has exacerbated the problem.

The white paper anticipates that up to 400 million people a year will pass through UK airports by 2020 and 500 million by 2030; fewer than 200 million do so today.

The SDC's report says that by no stretch of the imagination can increases of this kind be described as "sustainable".

The commission wants the Department for Transport to clarify the basis on which its forecasts of future greenhouse gas emissions from aircraft is based.

It says the department should also commission further research to resolve the substantial discrepancies between the different projections advanced by various organisations.

The Department for Transport, the SDC report said, should also reconsider its refusal to levy an emissions charge on all European flights pending the UK aviation sector's incorporation in 2008 into the EU emission trading scheme (EUETS), which is aimed at capping emissions.

The report calls on the department to explain more fully why such a charge would not be the best way of forcing the aviation industry to bear the full costs it imposes on the environment.

Sir Jonathon said: "The government has got to develop a far more joined-up approach on aviation, and that means the Department for Transport cannot pursue policies that cut across what the government is trying to achieve elsewhere...

"The huge expansion of airports and air traffic outlined in the white paper will render impossible government efforts to adhere to its own target of reducing carbon dioxide emissions by 60% by 2050."

The Department for Transport said it stood by its forecasts in its white paper.

"Our figures show that by 2050 UK international and domestic air transport greenhouse gas emissions could amount to about one third of all UK climate change impacts," a spokesman said.

"This is a large number, but nowhere near the 60% or 75% figures quoted in the report."