When a politician is accused of being “foolish”, “ill-informed” and not having “a clue what he's talking about”, you might expect the complaints to be legitimate. But such venomous language could also betray a different explanation: the politician may have rattled someone's cage. So it was last week, when aviation boss Michael O'Leary reacted furiously to comments made by Ian Pearson, the British government's hitherto low-key environment minister.

Pearson had accused Ryanair, the Irish budget airline that O'Leary runs, of doing too little to tackle climate change, memorably branding the airline “the irresponsible face of capitalism”. The fact that O'Leary protested rather too much was down to more than his well-earned reputation as a self-publicist. As pressure grows on the aviation industry, Ryanair and other airlines find themselves in an increasingly uncomfortable position.

The problem lies with two diverging industry trends. On the one hand, flying is more popular than ever before. British passenger numbers are predicted to double to 475 million per year by 2030, for example, and in China, according to the World Bank, passenger numbers grew by a whopping 28% from 2003 to 2004.

Progress in improving the fuel efficiency of aircraft is, by contrast, gradual. Current trends suggest that gains of 1–2% per year will be the norm for the foreseeable future. Only a step change in aeroengine design might increase this, but with current approaches being so safe and reliable, and change so expensive, that seems improbable.

As a result, the growth in aviation emissions, if left unchecked, is liable to wreck attempts to reduce greenhouse-gas emissions. In Britain, for example, airlines' emissions are growing by around 7% each year, even as the government prepares to set in law a commitment to cut national emissions to 60% below 1990 levels by 2050. According to the Tyndall Centre for Climate Change Research, the rest of the economy would have to move to zero emissions in order to sustain aviation growth and meet the target.

It is clear that something will have to give. If real cuts are to be made in carbon emissions, aviation growth will certainly have to level off. The number of trips may even need to be cut. These are truths that the airline industry does not want to hear.

The first moves towards such a future are now being made. The European Commission announced in December that it plans to include domestic flights in its carbon emissions trading scheme by 2011, with intercontinental flights joining the scheme the following year. This is a critical first step towards a future in which consumers start to pay for the environmental cost of flying.

For now, several European airlines say they are in favour of emissions trading, perhaps because they anticipate being eased gently into the scheme with relatively generous emissions targets. The full test of their support will come in the years after the scheme starts, when emissions will need to be capped tightly enough to reduce the growth in airline traffic.

But some, led by O'Leary's Ryanair, are opposed from the start. US airlines are sending an equally indignant message behind the scenes, Pearson says. This opposition may lead to a legal challenge from US airlines to the proposed inclusion of intercontinental flights.

European Commission officials say they are confident of the legality of their approach. But if the US legal action or non-cooperation of the airlines make emissions trading unworkable, more radical alternatives may have to be considered. One such approach would be to review European adherence to the 1947 Chicago Convention, the international agreement that prohibits the taxation of aviation fuel, and hence gives the industry a permanent advantage over its competition, such as rail travel. That would really give O'Leary and his allies something to squeal about.