Even if a whole raft of measures was introduced – including car sharing, some road charging, workplace travel plans, more public transport and increased home working – on an unlimited budget and as soon as possible, carbon emissions from transport in 2020 will only remain similar to present levels.

Currently, 24 per cent of Yorkshire's carbon emissions come from transport, with the region committed to reducing its total levels of CO2 by 25 per cent by 2015, and 80 per cent by 2050.

A new study by the Yorkshire and Humber Assembly attempted to show how this may be achieved but in a startling conclusion, its strategists admit that, even with unlimited funding for new schemes and with projects being fast-tracked, the best that can be hoped for is that by 2021 carbon emission levels return to the 2008 rate.

Arthur Barker, chairman of the assembly's sustainable development committee, said: "To all intents and purposes this is a very challenging report.

"It will inspire an awful lot of thinking in this region but these problems will be addressed. There are a lot of suggestions in the report that we can implement now, and we can bring in some of the harder things as and when we get the finance from central government.

"There are some things, however, that will not be politically or publicly acceptable, which this report makes clear. And it may be that we have to start looking at alternative ways of reducing carbon in this region, perhaps through making sure every home is insulated."

The assembly study concludes that it is impossible to reduce the region's emissions through transport to the target 2021 level, the equivalent of 2.5 tonnes per person, and the best that could be hoped for is the current level of 2.8 tonnes.

But with limited money available and an unwillingness from the Government to fund major public transport schemes, a far more likely scenario is that carbon emissions from transport continue to grow as they have been, with the levels projected to reach four tonnes per person by 2021.

The report shows that no one option would result in a radical reduction in emissions and that the only way to cut carbon would be to introduce a wide-ranging package of up to 26 measures.

There are, however, wide discrepancies between the popularity of the different options; while some would prove cheap and popular, others would be widely reviled and could have catastrophic effects on the region's economy.

Most popular would be to bring in better planning rules so that new development actively reduced the need to travel far. Other favoured measures include introducing school and work travel plans; encouraging more walking and cycling; and improving bus services.

Least popular were plans to ration the amount of carbon each person could emit; constrain housing growth and air travel; bring in road mileage and congestion charging; and introduce car-free zones.

But the report's authors say that it is only by introducing all 26 measures, popular or not, that Yorkshire's carbon emissions from transport could be brought down.

Even that would not necessarily stop the region's emissions from increasing.

People might spend the money saved by walking or cycling to work instead of using their car on consumer items which might be produced overseas and air-freighted into the country.

Or people may put the money saved towards a short-haul flight for a weekend break.

Even if all 26 measures were to be introduced, the carbon emissions from transport would still increase dramatically from today's levels in some rural areas, most notably Selby, Ryedale, Richmond, Hambleton, Craven and the East Riding.

However, the report adds: "The picture is not universally bleak, as the interventions do make an impact on carbon emissions."

With large-scale implementation, action in the region could make a difference, it adds.