A quarter of all those in Europe who are affected by aircraft noise live under the Heathrow flight-path. If there is a single statistic which underlines the failure of British aviation policy it is this. For decades, a combination of powerful lobbyists and weak decision-making has led ministers to slavishly accept the hodgepodge expansion of Heathrow. There has been very little vision, and very little evidence-based policy making.

The previous Labour government, for example, decided to build a third runway at Heathrow, and only then asked the independent Committee on Climate Change (CCC) to figure out how the UK could meet its 2050 carbon reduction target. They didn't allow the facts to affect their policy. But the CCC did some very useful work, and calculated that, based on increased plane loads, new technology and fuel improvements, our carbon budget allows for about a 60% increase on current passenger numbers, bringing us to around 368 million passengers per annum. This is still a very large increase in the proportion of our carbon emissions due to aviation – the industry would emit 37.5MtCO2 a year by 2050. It is harder to decarbonise aviation than other sectors. But this 60% increase represents a lot of opportunities for new destinations and new travellers - within our carbon cap.

So, how much new capacity do we need to build to take us up to this limit? The answer is none. We can reach that 60% increase with no third runway at Heathrow, no new Thames Estuary airport, no second runway at Gatwick or Stansted. And Department for Transport forecasts suggest that we won't get to that point until about 2030. In particular, Gatwick is already expanding into new markets with routes to China, South Korea and Vietnam. Stansted is only around 50% full, and it makes no sense whatsoever to build a second runway at either. Indeed, rather than pushing for new runways, both airports are campaigning for rail links and improved surface access to help their growth, which brings environmental gains too: up to half of emissions from aviation actually come from surface movements, rather than the planes.

It’s clear that Heathrow plays a very important role - it is our only hub airport, and caters for transfer passengers, particularly business users, and that enables flights to emerging markets to become economically viable. It’s also true that Heathrow is almost totally full. While in the short term there are a few tools available to encourage flights to transfer to Gatwick or Stansted, if we are to retain a successful hub airport and all the benefits it brings, we need to look at longer-term solutions. Mixed Mode operation and a large increase in night flights have been proposed, but they fail the same test as the third runway - they affect far too many people who already suffer massively from noise pollution. And it has a huge effect on London’s air quality. Heathrow is, simply put, in the wrong location for our current needs.

Boris Johnson, I suspect for electoral reasons, recognises that Heathrow is not the answer. But his solution is perhaps even more wrong. Located east of London in the Thames estuary, 'Boris Island' would be largely inaccessible for anyone living outside London and the south east, making it even harder to spread economic growth to the north and west of the country. It would essentially be a transfer hub for foreign travellers (paying no APD) and the City. Before construction could even begin, you'd have to somehow move or defuse the remains of the SS Richard Montgomery, a wartime liberty ship whose detonation would cause a small tidal wave up the Thames and possibly one of the world's largest non-nuclear blasts. The chance of bird-strike is also 12 times higher here, let alone the crippling effect it would have on this vital migratory route. The RSPB claimed it would be one of the worst environmental decisions the country has made. Finally, the expense of this project would be astronomical and it would take far too long to construct. You'd have to start the infrastructure from scratch. It's simply not a goer, and I am delighted that I and the Lib Dems rejected it so promptly.

Is there a better option? We have to be clear that total UK aircraft movements in 2050 cannot be above the limit suggested by the CCC. So there is no point in building capacity which would allow us to vastly exceed that limit. Our 2050 carbon reduction target is not some figure that can be fiddled if a future government realises they can't meet it. The effect on our children's economy and their environment would be immense. We must not burden them with an environmental debt from which they cannot escape. But that still leaves us with a 60% increase in passenger movements which is allowed within UK carbon budgets.

For now, we can meet it with the runways we have, using the capacity at Manchester and Birmingham, for example, but it makes sense to consider the option of having a new hub, bringing together runways in one place to link with all the transfer passengers and new routes they bring to bear. That new hub could only happen with the closure of other runways and airports to ensure a future government doesn't exceed the available carbon budget. And this new hub couldn't be just anywhere - it would have to be accessible to north and south of the country, and be somewhere which would pose minimal impact to the local population and to the local environment.

The Labour Party is at best vague on this - they "accept the Government’s decision to cancel the third runway at Heathrow" - but fail to say whether they actually support it or don't - and many of their backbenchers (and frontbenchers) still argue for the third runway. They also argue for more expansion of aviation in the south east, threatening to breach our environmental constraints.

Some Tories, such as the Transport Secretary, Justine Greening, understand the need for environmental considerations to play a key role in aviation policy, in keeping with the Coalition Agreement, but there is a growing band of pro-third runway MPs, including George Osborne. Few seem to take Boris Island that seriously.

This autumn, the Liberal Democrats will vote on a conference motion that presents a proper policy to the public, outside of the vested interests in the aviation industry. The public deserve an airport policy which balances the benefits from aviation with the harm it can do to the environment globally and locally. That is exactly what we’ll deliver.