Leading article: We all have an interest in the outcome of this battle

The battle over Stansted airport has been rumbling on for several years now. But from yesterday it reached a new intensity. Last year, Uttlesford District Council rejected a planning application by Stansted's owner, BAA, to expand the airport's capacity. BAA appealed and now the issue will be decided by a local public inquiry. There will be no quick decision. The inquiry will run until October. But with evidence mounting that climate change is already beginning to bite, the result of this inquiry will send out a significant message about our national priorities.

BAA's argument is uncomplicated. It wants to increase its passenger numbers by 10 million a year, and justifies this on the grounds that the expansion will boost the UK's economic growth. The environmental arguments on the other side are just as simple. The expansion would be a threat to local wildlife, increase pollution, and, most damagingly, help to accelerate global warming.

It is undeniable that aviation helps the economy in the short term. Some 200,000 jobs in Britain are directly or indirectly related to aviation. And the sector contributes around £11bn annually to our national income. The Stansted expansion alone would create an additional 5,000 jobs. Aviation also underpins tourism, another vital contributor to Britain's economy. Around 30 million overseas visitors came to the UK in 2005, spending £14bn. More than two thirds arrived by air. But, as last year's report by Sir Nicholas Stern made clear, the economic costs for Britain of a substantially warmer world will outweigh such economic benefits.

The aviation industry points out that aviation accounts for only 3 per cent of global emissions. But this ignores the formidable rate of growth we have witnessed in recent decades. The number of people around the world taking flights more than tripled between 1978 and 1999, from 45 million to 150 million. If aviation traffic continues to expand at this rate, as it will unless checked, it will wipe out all the emissions savings we might squeeze from other sectors.

So we must hope that BAA's proposals are rejected by this inquiry. At the same time we must remember that Stansted is merely one climate threat among many. Some 30 airports in the UK have major expansion plans. What is needed is a national policy from the Government to curb the growth of air travel.

At the moment, ministers are giving out perilously conflicting signals. The Government has pledged to reduce emissions by 60 per cent on 1990 levels by the middle of the century. It has also begun to raise airport tax (although timidly). But a White Paper on air transport in 2003 seemed to approve a significant expansion of Britain's regional airports. Another policy document last week proposed centralising planning inquiries for major projects - a category that would include airports.

There are worrying signs that the Government is hoping to bypass democratic inquiries of the sort we are seeing over Stansted. Unveiling the White Paper on planning last week, the Communities Secretary, Ruth Kelly, tellingly bemoaned the fact that the fifth terminal at Heathrow had been delayed for so long by such an inquiry. Meanwhile, civil servants are working on the assumption that the number of passengers passing through UK airports will rise from 228 million to 490 million by 2030.

This is the opposite of joined-up government. Ministers cannot have it both ways when it comes to aviation growth and climate change. And nor can we, the public. It is us driving the demand for all these extra flights. The battle over Stansted may seem parochial, but it is a fight in which we all have a stake.