SOARING car and air travel must be tackled if the world is to stop greenhouse gas emissions from transport rising rapidly over the next few decades, according to a leaked draft report by the United Nations' climate panel.
The document, to be issued on 4 May in Bangkok by the Intergovernmental Panel on Climate Change (IPCC), says governments are running short of time to avert big temperature rises, threatening more droughts, heatwaves, floods and rising seas.
It highlights transport as a particular problem area, saying efforts to curb emissions "are faced with many barriers", despite options such as new engine technologies or biofuels.
Transport, mostly cars and lorries, accounted for 26 per cent of total world energy use in 2004.
Unless there is a major shift in policies, the report says "projections foresee a continued growth in world transportation energy use by 2 per cent a year, with energy use and carbon emissions about 80 per cent above 2002 levels by 2030".
The 101-page technical summary warns: "Transport activity is expected to grow robustly over the next several decades."
In some industrialised nations, car ownership is already five to eight for every ten people - ten to 100 times more than in developing states.
The study projects that biofuels could rise to 3 per cent of total transport fuel by 2030 or to 10 per cent if a penalty for emitting heat-trapping carbon dioxide was set at $25 (12.70) a tonne.
Measures such as tighter vehicle efficiency standards, lighter materials and better aerodynamics could double the fuel economy of new vehicles by 2030, roughly halving their emissions.
The report also foresees more use of hybrid cars, but says that the outlook for hydrogen powered vehicles is uncertain. The rise in aviation emissions was also raised. Currently about 2 per cent of total carbon dioxide emissions from human activities come from aviation.
Emissions from this sector are likely to rise by 3 to 4 per cent a year given projected annual traffic growth of 5 per cent, outpacing annual improvements in aircraft fuel efficiency of 1 to 2 per cent, it says.
But planes also damage the climate in other ways, partly by emitting heat-trapping nitrous oxides at high altitude.
"These effects are estimated to be about two to four times greater than those of aviation's carbon dioxide alone," it says.
Other estimates have put aviation's share of greenhouse gases at about 5 per cent, or roughly 2.4 times the carbon figure. The report says extra charges for fuel or the inclusion of the aviation sector into a greenhouse gas trading system "would have the potential to reduce emissions considerably".
It suggests that viewing the fight against global warming as an economic problem and not purely an environmental issue would help to achieve greater progress.
Dr Richard Dixon, of WWF Scotland, said he hoped the IPCC's emphasis on transport would send a "very strong message that transport really is the sector that's running away without control".
He continued: "We really haven't got a grip on transport and this is exactly the dilemma you see in all the manifestos of the main [Scottish political] parties."
The manifestos talked about the need to take action to address climate change, he said, but "then you read the transport bit and see 'we'd like more roads and for people to fly to Scotland on holiday'.
"There are clearly civil servants in governments who know this is an issue, but there are ministers who have been turning a blind eye or perhaps don't know."
Dr Dixon said he had been stunned to find out that one in five international flights in the world touch down in the UK and pointed to plans at airports across the country to expand.
"We are actually the nation which should really be getting a grip on what do to with aviation," he said.
"Glasgow and Edinburgh airports are growing in double figures - 10 per cent a year - so we really are at the heart of aviation growth.
"Aviation has really had no attention put on it. Probably it's about 5 per cent of the problem and it is growing very rapidly.
"In ten years, people are going to look back and say 'hang on, we knew aviation was small, but growing very rapidly - why didn't we do something... look where it is now'.
"We'd be insane to ignore the warnings."