The Big Question: Does Heathrow Airport really need another runway and terminal?

Why are we talking about this now?

Hundreds, perhaps thousands, of activists are gathering at Heathrow at the "Camp for Climate Action", which opened yesterday. They're protesting against the damage aviation is doing to the planet and in particular to object to the planned expansion of Heathrow, with the new Terminal 5 due to open next year and a third runway to be installed by 2020. A roughly equivalent number of Metropolitan Police officers are expected to keep an eye on the radicals.

Who's trying to stop it?

The gathering is taking place against the wishes of the Government and BAA, who have taken legal action. The owners of the land, Imperial College London, have declared the protest illegal. Sunday will see a day of "direct action". There is much speculation about tactics, with plans for disruptive bomb hoaxes denied by protesters. Impersonation of passengers and flight crew is more likely. Even minimal disruption could prove to be frustrating for genuine users. BAA, which owns Heathrow, recently gained an injunction banning protest group Plane Stupid from the airport and its environs, but other groups were allowed to demonstrate provided they do not disrupt operations.

Are the protesters right?

Leaving aside the desirability of ruining family holidays, they have a point. Aviation accounts for a small (7 per cent in the UK, 2 per cent globally) but rapidly growing proportion of our carbon dioxide and other harmful emissions. This year 50 times more people will travel by air than 50 years ago. Liberalisation ("open skies") and cheap, no-frills operators such as Ryanair are two more engines of growth.

What are governments doing?

Not that much. Aviation fuel is not taxed, by international agreement, and air travel is not yet within the EU's carbon trading scheme and it lies outside the Kyoto protocol. It appears that while sectors such as the auto industry and the electricity, oil and gas companies are being targeted by governments to clean up their act, airports and airlines are allowed to indulge their dirty habits.

Why Heathrow?

Heathrow Airport, squalid as it is, remains the world's busiest international airport, with 67.7 million passengers passing through it each year on 469,560 flights. It accounts for almost 30 per cent per cent of UK air passenger activity. In 2005, more than 35 per cent of Heathrow's passengers were business travellers - according to the Government "directly supporting the international competitiveness of London and the wider economy" - and 55 per cent by volume of all air freight comes via Heathrow.

Why do they need another runway?

Demand at Heathrow is now far in excess of runway capacity. So passenger growth at Heathrow in past few years has been artificially limited to just 5 per cent compared to 27 per cent at UK airports overall. Heathrow is in an increasingly uncompetitive position in relation to other major European airports. Although it handles more passengers per year than any other European counterpart, it has less runway capacity than competing major European hub airports

What's to be said for Heathrow expansion?

Plenty. The economic importance of Heathrow can hardly be overstated. It supports the economy generally and in particular London's status as a great city. The airport is economically significant in its own right, employing about 100,000. The aviation industry accounts for about 200,000 jobs. Notwithstanding terror attacks (and climate protesters) the long-term growth of air travel, globally, is about 5 to 10 per cent a year. Does the UK want its share of that action?

What happens if Heathrow stagnates?

We lose out as other EU countries may prove less scrupulous about green concerns. Airports in Amsterdam (Schipol) and Paris (Charles de Gaulle) now operate five and four runways respectively, and a fourth runway is planned for Frankfurt (Main). It's an international business, too. Over the next five years, China plans to invest $17.5bn (£8.7bn) on launching 71 airport-expansion projects, relocating 11 airports and building 49 new airports. Some Gulf states are also building up their role as transcontinental hubs. Many believe that whatever happens in the UK or the EU, our pollution is a fleabite by comparison with what's happening in east Asia.

What about expanding other airports?

The 2003 White Paper "The Future of Air Transport" set out the Government's plans to expand Stansted, with one additional runway, as well as some regional airports. Ministers are clearly committed to increasing capacity at Heathrow because it "would have a higher economic value than at any other UK airport". But "only if we can be confident of meeting the strict environmental conditions". The anti-aviation lobby claims that the Government's plans for air travel are inconsistent with their targets for reducing CO2 emissions. A Manchester University study for Friends of the Earth suggested that the total CO2 discharges from air traffic would offset all the reductions in carbon emissions scheduled under British Government policies to comply with Kyoto.

Will technology help?

Slowly. Rolls-Royce, a British company with a good deal to lose from any contraction in demand for their aero engines, say that jet engines are becoming more fuel efficient at a rate of 1 per cent a year. Hydrogen fuel cells could also help, but these are barely practical in cars let alone aircraft.

Any other ideas?

The Conservatives' leader, David Cameron, has suggested a "green air miles allowance" for each citizen which, if exceeded, would attract taxes. The Conservatives also want to charge fuel duty and/or VAT on domestic flights; replacing air passenger duty with a per-flight tax based on actual carbon emissions. The Liberal Democrats have long favoured a carbon tax. The Government has doubled air passenger duty (to £10 per flight) and plans to increase it still further for longer-haul flights. Reading between the lines of the policy documents it seems that this solution will eventually be implemented. Failing that there's always the Flight Pledge Union (www.flightpledge.org.uk) where you can simply promise not to get on a plane.

Do the environmental protesters have a case?

Yes...

* Aviation is the fastest-growing source of carbon emissions, and has to be curbed

* Pollution in the atmosphere is far more damaging than that at ground level

* Heathrow Airport is already too big, too noisy and too disruptive of life in the South-east

No...

* The damage to the planet is exaggerated; cars and coal-powered stations in China do more harm

* Heathrow is vital to the British economy; 100,000 jobs depend upon it

* If we don't expand Heathrow, the business will simply go to Amsterdam or Paris

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