Planned your summer break yet? Four out of five people are refusing to let the recession deter them from taking a holiday, saying they are essential rather than a luxury, according to a survey.

For many people, that means jetting off somewhere hot and sunny. But how does taking a flight square with your green conscience these days?

For anyone concerned about climate change, flying is increasingly becoming the kind of guilty secret, such as picking your nose, they don't like to admit to others.

It is increasingly something to be ashamed of, because we know how damaging it is to the environment.

Air travel contributes 13 per cent of the UK's CO2 emissions, according to Government figures. Pretty low, you might think, compared with housing – responsible for almost a third.

But in terms of damage to the climate, flying is much worse than, for instance, taking the train, say campaigners. More worrying still, aviation is one of the fastest growing contributors to climate change.

Between 1990 and 2050, emissions from aviation are set to quadruple and scientists say that will negate all our attempts to save emissions in every other sector.

Indeed, so serious is the threat posed by aviation that some observers believe the only solution is to ration the number of flights we are allowed to take.

Short-haul flights, in particular, are singled out for criticism.

While you could argue you need to fly if you are travelling to Australia, the arguments are far less convincing when you're going from Bristol to Manchester. Last year, 25 million people took domestic flights in the UK.

Two years ago, the Conservatives suggested giving individuals an annual allowance of short-haul flights, with further flights heavily taxed. But the policy was quietly dropped after widespread criticism.

However, the idea has come up again – and this time from Lord Turner, chairman of the Government's Committee on Climate Change.

Speaking to the Commons environmental audit committee last month, he said people would have to accept personal flight limits: "We will have to constrain demand in an absolute sense, with people not allowed to make as many journeys as they could in an unconstrained manner." Neatly positioned right at the heart of this highly topical – and very controversial – issue is Bristol International Airport which plans to increase passenger numbers from 6.22 million last year to 10m by 2016.

Although fewer people used airports in Britain last year, Bristol saw a rise in passenger numbers of nearly six per cent. While those numbers fell sharply in December, January and February, it is confident of the future for air travel and next month, it intends to lodge a major planning application for its expansion with North Somerset Council, followed by a three-week consultation.

Preparing to vehemently oppose the plans is the Stop Bristol Airport Expansion (SBAE) alliance, composed of Bristol Friends of the Earth, the Campaign to Protect Rural England, the Parish Councils Airport Association and other groups in the area.

SBAE is worried about the pollution and noise caused to people living nearby by an extra four million passengers a year, as well as the need to build on greenfield sites. It also believes expanding the airport will damage the local economy, particularly tourism, because more people will be enticed abroad.

But the main reason for SBAE's objection is the very serious damage to the environment caused by increasing flights.

SBAE says the airport's emissions will nearly double from 430,000 tonnes of CO2 (more than all the road transport in Bristol) in 2005 to 730,000 tonnes by 2019.

That is simply unacceptable at a time when everyone else is being asked to help the Government meet its target of cutting the UK's emissions by 80 per cent by 2050, according to spokesman Jeremy Birch.

He said: "Flying is the most carbon-intensive form of travel. Over a single 1,500km (932-mile) journey, an aircraft emits twice as much greenhouse gas per passenger-kilometre as a high-speed train.

"Shorter journeys produce even higher emissions per kilometre."

He points out that Bristol airport's emissions already exceed those of developing nations such as the Gambia, Grenada and Chad.

He added: "Many of these countries will suffer some of the harshest impact of climate change – yet they are powerless to tackle the growing impact of cheap flights."

Bristol airport's planning and environment director Alan Davies accepts aviation has an environmental impact but says it is about balancing the benefits of air travel while addressing the green issues.

He said: "The industry is working to targets for planes to be 50 per cent more fuel efficient by 2020.

"On the ground, our objectives are to ensure airport emissions do not exceed 2007 levels and 20 per cent of the additional energy required by the proposed development is sourced from on-site renewable sources."

He adds that UK flights are responsible for less than 0.1 per cent of aviation's global contribution to carbon emissions.

Whatever the outcome of this battle between Bristol airport and anti-expansion campaigners, there is no doubt that flying poses increasingly difficult questions for all of us.

We've come to see our holidays abroad as practically a human right.

Indeed, a 2006 Government survey found 90 per cent of people thought they should be free to fly as much as they wanted.

But when the phrase "even if this harms the environment" was added to the question, the number dropped to just over 40 per cent.

Flying is no longer a simple way of getting from A to B. It is now an ethical issue we all must face – or deal with the consequences.

For more information, visit www.bristolairport.co.uk.