Believe me, even as a politician, I can see that there are extremely good reasons for asking the question above, and sadly some extremely good reasons for feeling a little bit dismal about the answer. Based on experience to date it's certainly true that politicians haven't got a very good track record of thinking beyond the next five year election horizon, of taking risks, of challenging corporations, of really standing up and taking real leadership. And that's the case even when, in theory at least, there are supposed to be politicians out there who genuinely know what the stakes are with climate change. Politicians like Tony Blair who, for all his many faults which we can spend a lot of time discussing, did at least commission that incredibly important conference in Exeter in February 2005, which told him in no uncertain terms that we essentially have ten years in which to act to make a real difference to climate change. And if we don't use that next ten-year period then we're going to have the nightmare scenario – of which we saw a glimpse with Hurricane Katrina.

We have a Prime Minister who knows all of this, he's heard what the scientists are saying, he says that climate change is the greatest threat that we face, he says that tackling it is going to be a priority for his government, he says that he's going to exercise international leadership on the subject. And yet we all know CO2 emissions have actually risen under this government, not declined; that this is a Prime Minister who had personally intervened on the side of the Department for Trade and Industry and against the Department for the Environment about how many emissions British industry could be allowed to emit under the European Union Emissions trading system. In fact, we've just had the dismal news yesterday that the European court has actually ruled in favour of Britain, so he's going to get away with it. The Guardian reported this with the headline 'UK victory rips hole in EU's pollution trading scheme'.

Furthermore, he is a Prime Minister who has backed a massive expansion in the aviation industry, knowing full well that aviation is the fastest growing source of greenhouse gas emissions. He has also embarked on a major new road building programme. As if this wasn't enough, we commissioned a report recently by the Association for the Conservation of Energy. This report was looking at how well the Government had implemented existing European legislation on energy efficiency issues, and they pointed out that this is a government that has delayed implementation of the energy performance of buildings directive, has failed to set binding targets for energy demand reduction under the energy services directive, and has failed to promote small scale combined heat and power in line with the Co-generation Directive. This doesn't sound very much like international leadership to me.

And so, yes, I can well understand why people ask the question, 'will politicians save us from climate change?'

And yet my answer has to be that they certainly could save us from the worst of climate change - given sufficient political will I think politicians could set the framework that would help us to avoid it. But it comes back to that political will, which means that public pressure has to be strong enough, and so we have a responsibility to generate that pressure. In the end, I think political action is an essential component, but not a sufficient one, and we need grass-roots actions as well.

The reason why political action is an essential component is that we need a policy framework including fiscal measures, tax measures, and including regulation, that will help us to get on a more sustainable path as fast as possible. Individual action is also essential, but without a binding legislative framework, I'm not convinced that we'll get to be where we need to be fast enough. And I would just underline the urgency of this debate. Sometimes when you hear politicians talking you would think we had forever to get it right. We don't have forever, we have a very short time, and that's why I think we need that legislative, binding framework to help us move in the right direction. Because as individuals, we're all of us, or at least most of us, too contradictory and too unreliable - we tend to fail to act if we think that our own actions might be offset by other people who aren't dong their bit. It sometimes feels that our contribution is going to be too small to be significant. So if individuals manifest that degree of paradox, then I think its clear that the sort of profound disconnection for which I've just been criticising Tony Blair, between what he says and what he does, doesn't demonstrate that he's in any way insane, it demonstrates in a sense, sadly, that he's all too human.

We can verify this, because in opinion polls around 85% of the British public regularly say that they're concerned about climate change, and yet domestic energy consumption still rises by about 2% a year, cars are getting bigger, people are flying further away on holidays more often. And so Mr Blair is, like so many of us, in a state of denial. One of the ways to recognise that we need to make change, one of the ways to get through this denial, is to make it clear that the policies that we need to deal with climate change are in fact positive changes that in many cases we need to see anyway. That the actions are desirable in themselves. That a low carbon future isn't about shivering around a candle in a cave, but its actually about a positive future – there is a positive vision that we can paint about what a low carbon future is going to be like. And it seems to me that if we can get that message across, then we stand at least a chance of persuading politicians to address this issue.

But let me just go back to the beginning, and the fact that every time you open a newspaper, there's another terrifying headline. A recent one in the Independent was headlined 'Melting Planet' and warned of erosion of polar ice, and of species dying out faster than we dared recognize. Other stories warn us of mass migration, mass starvation, and the spread of tropical diseases. And increasingly these headlines are found not just on the environment pages – there is a growing recognition that we're not just talking about an environmental crisis, but an economic crisis, a social crisis, and perhaps more than anything else, a development crisis as well. Because it's already quite clear that climate change threatens to tear apart most efforts towards development in some of the poorest countries of the world. The Intergovernmental Panel on Climate Change predicts:' The effects of climate change are expected to be greatest in developing countries in terms of loss of life, and relative effects on investment and economy.' It describes Africa, the world's poorest region, as the continent most vulnerable to the impacts of projected change because widespread poverty limits adaptation capabilities. And that's what makes climate change not just a scientific challenge, not even just a political challenge, but a moral challenge as well. Because what we're talking about is changing patterns of consumption and production now in order to reduce threats not just to ourselves, but perhaps even more to our children, to future generations, and to people living on the other side of the world. And I think the terms of that challenge can be expressed really very simply. Are we going to be able to build the public and political will to act fast enough, to be able to act in an equitable and radical way, or will we simply go down in history as the species that spent all its time monitoring its own extinction rather than taking steps to avert it?

The Intergovernmental Panel on Climate Change report of 2001 predicts that the world's temperature is likely to increase by 1.4 – 5.8 degrees centigrade minimum over the period 1990 to 2100. Since that's the projection for the average global surface temperature, which includes sea surface, its very likely that nearly all land areas will actually warm to a greater extent than that. Since that prediction from the IPCC in 2001, we've become much more aware of all the different possible feedback loops, and so it looks like in some parts of the world we could be seeing areas of land where the temperatures are rising by 10 degrees centigrade. If you bear in mind the global temperature difference between the last ice age and present time was around 5-6 degrees centigrade, then its clear that the sort of warming that we face is a terrifying prospect indeed. And it's one towards which we are sleepwalking. Most people, and almost all politicians, are in denial. The targets set by governments and the Kyoto protocol are hopelessly inadequate. Even worse, our own government seems to have given up the pretence of even trying to set future targets. Tony Blair was reported just a few weeks ago as saying: "Legally binding targets make people very nervous and very worried". Well I've got news for him. The absence of legally binding targets makes people pretty nervous as well.

And actually Blair's words aren't even true, because there are sections of business that are actually asking for a level playing field, that are asking for certainty, that are asking for some stronger regulation. Targets and technology are not two different options as Blair seems to suggest. It is precisely the targets that lead to the innnovation, which in turn spurs the new technologies. However, even the target that most governments give lipservice to, while being far from achieving, is a 60% cut of greenhouse gas (GHG) emissions by 2050. But that figure, drawn from that earlier IPCC report, is a global average. To make cuts in an equitable way, in recognition that we in the industrialised countries are disproportionately responsible for climate change and therefore have a disproportionate responsibility to do something about it, and to take into account more recent science, then it's very clear that we need cuts in the order of 80-90% of our GHG emissions by 2050.

To achieve that will require nothing less than a revolution in the way that we run our economy, the way we measure human welfare, and the way we produce and consume. And I use that word revolution, with its admittedly military overtones, with advisedness, as I believe that to build momentum for the changes we urgently need, we need to broaden our concept of security away from just military security, to recognising the broader concept of environmental security as well. Significantly even the Pentagon now admits that climate change is a far greater threat to our future than international terrorism, and government advisors on both sides of the Atlantic are recognising that climate change is itself a weapon of mass destruction. Certainly it's very clear that if George Bush and Tony Blair had spent just a fraction of the political commitment and resources than they expended on an illegal war in Iraq on tackling climate change, then we might have had a real chance of the world being a safer place.

So the steps that we need to take are I think very clear - and actually very straightforward. A massive investment in energy conservation, major investments in renewable energies, internalisation of environmental costs, a switch of funding into public transport instead of more roads and expansion, a more coherent planing and housing policy, more energy efficiency. This isn't rocket science, we just need to get on and do it.

Greenpeace has recently reported that the EU could save over 40% of its primary energy demand using existing energy efficiency measures, and that over half of our remaining energy demand could be met through renewable energies by 2050. This simply underlines that we do not need nuclear. Nuclear is uneconomic, its unnecessary, and its very clear that there is no way that it is going to get us out of this hole. But it's also clear that technical fixes alone won't be enough. Yes we need efficiency, yes we need technology, but the Government's Sustainable Development Commission itself reported recently: 'the overwhelming consensus amongst academics, is that resource productivity will not on its own deliver the desired reconciliation between the pursuit of economic growth, and the imperatives of learning to live within the earth's biophysical constraints and carrying capacities'. That's a very academic way of saying, basically, that the current economic model is stuffed. That we cannot go on growing our way out of the problem, because even if you make individual cars and planes more efficient, the increasing volume of them, in the skies and on the roads, will offset any increases in efficiency.

If you're in any doubt about that then just consider for a moment the extraordinary growth of a country like China, that's now overtaken the United States as the world's leading consumer of four out of the five basic commodities – on grain, meat, coal and steel. It will overtake the US in its consumption of oil by 2025. On current trends, by 2031, China will be consuming 99 million barrels of oil a day. That doesn't mean very much until you realise that the total world production today is only 84 million barrels per day.

By that same date, China would have 1.1 billion cars if it matches US current trends. If it had those 1.1 billion cars, that would be more cars in China alone than the total number of cars on all the roads in all the countries that there are today in the rest of the world. And to say that isn't to criticise China, it's simply to point to the same development model that we have, and that it is fundamentally unsustainable, and that we in the industrialised world have a greater responsibility to change.

And so to achieve those cuts of 80-90% reduction in greenhouse gas emissions by 2050, we don't just need different technologies, we need different cultures, different economies, different expectations - in short nothing less than a completely different way of life. Briefly, I want to suggest one of the policy tools that might help us get into that different way of life. There's increasing interest now around the idea of a system of domestic carbon rationing, or domestic tradable quotas as they're sometimes known. Basically, these domestic tradable quotas would mirror at a national level the logic of contraction and convergence at a global level. Under Contraction and Convergence methodology, equity, in terms of equal per capita emission shares, is built into a system where international agreement is reached about what level of total greenhouse gas emissions is compatible with a safe environment, then global convergence to equal per capita shares of that total amount is worked out towards a particular date.

That means that developed countries dramatically reduce the amount of CO2 emissions that they emit, while allowing poorer countries to emit more in the short term until we average out, in about 30 or 40 years time. Carbon rationing at a national level would mirror that system, looking in particular at personal transport and household energy. It could mean that people would simply be issued a carbon card, like a credit card, that they would swipe if they're buying petrol for their car, or if they're buying a rail ticket or an air ticket. At the same time energy bills would subtract the relevant rations from that individual's total allocation. The rations would be tradable, so that poor people who tend to use less energy, would benefit financially from selling their shares to those for whom cuts in energy use are harder to make initially. But crucially there would be fewer rations allocated each year, in order to bring consumption down to more sustainable levels. One of the major advantages of this system is that it's arguably fairer than energy taxation, as richer people can't forever buy themselves the right to pollute. At the moment it's very easy for richer people to carry on with business as usual, because essentially they can afford the green taxes.

It also, I think, engenders a sense of everyone making the changes together. Meyer Hillman, who's done a lot of work on this, deliberately uses the word 'rationing', which puts other people off, because he wants to summon the feeling that existed in the Second World War, when people were pulling together because everyone was rationing. There wasn't an outcry when food rationing came in, because everybody recognised the nature of the threat, and they recognised that there was a roughly fair way of addressing it. We need something similar to deal with climate change.

I realise that for some people this sounds draconian – like some kind of green Orwellian nightmare. To that, I simply challenge you to come up with another system, based on equity and social justice, that will change human behaviour effectively. All the evidence shows that we can't rely on goodwill and voluntary measures alone.

Of course the real challenge, which is what tonight is all about, is how we persuade the public and the politicians to face up to this reality. The fact that poverty campaigners and environment campaigners are working together in the Stop Climate Chaos campaign is a fantastic piece of news, that people are beginning to see the links in all their different campaigns that they're working on, and recognising that social and environmental justice are absolutely and inextricably linked. But there are many challenges ahead, and I think a very real problem is that by emphasising the apocalyptic vision of climate change, we simply frighten people into paralysis. For many people, all they can think to do, the only sensible response, is to go down the pub and forget about it. I passionately believe that we won't make progress if we talk about climate change only in terms of giving things up. Tony Blair was spectacularly guilty of this just a few weeks ago when he announced: 'the blunt truth about the politics of climate change is that no country will want to sacrifice its economy in order to meet this challenge'.

There are at least two immediate responses to this. Firstly, that the economic costs of not acting are far higher than the economic costs of investing in action today, and secondly that there's no good reason why anyone's economy has to be sacrificed. There are a great many win –win solutions out there, and its crucial that we highlight them. Energy efficiency for example isn't some sacrifice, energy efficiency is actually great for people living in poverty, its great for the environment, it's great for the economy. We simply won't be successful unless we sell a positive vision about the benefits of a low carbon future, and I think that's what we have to really underline. That our future vision doesn't have to be a bleak or a frightening one, if we work towards it constructively and hopefully. A low carbon world for example would be a very labour intensive world, there would be much less unemployment. Some jobs would almost certainly be lost, in some of the more energy intensive industries, but those would be more than made up for by jobs in an economy based on repair, recycling and re-use.

A low carbon world is one of strong local communities - there would be less long distance commuting, fewer dormitory towns and villages, greater local production and consumption, thriving local businesses. A low carbon future would be one where social and environmental justice could meet. People unable to heat their owns homes would find it easier to get their homes insulated. And, furthermore, a low carbon world would be a much safer world. We hardly need to be reminded that much of current foreign policy in the west is about securing access to fossil fuel resources which are often in very unstable parts of the world.

If we were far more self sufficient in energy resources there would be far fewer resource conflicts, and I think it likely that we would never have had the Iraq war. And perhaps more controversially, I think a low carbon world might just be a world in which we're actually happier. Now that might be a heretical thing to say, but I'd remind you of Andrew Marr's quote: 'if politics isn't about happiness, then what's the point of politics?' Clearly in poorer developing countries a certain quantity and quality of economic growth is still urgently needed. But in the richer countries once our basic needs are met, it seems that more money doesn't make us happier. There's plenty of research from groups like the New Economics Foundation and others, which shows that one of the reasons for this is that we're constantly moving the goalposts, so as we get richer we're simply comparing ourselves to other people. We're constantly in this state of dissatisfaction. So that the policies we need are those that allow us to reclaim our time, rather than working longer hours to produce more goods that don't make us happy. So much of us spend so much of our time working to earn more income, that we overlook the fact that some of us might be happier having the time for ourselves our family and our friends. Not many people, lying on their deathbeds, look back and think 'my god I wish I'd spent more time in the office', but they do wish they'd spent more time with friends and loved ones.

We need an education system that enables people to realise their full potential instead of training people for little boxes of jobs. We need policies to discourage materialism and promote authentic advertising. It's patently obvious that switching brands of soap, or buying a new car doesn't make us more sexy or attractive, and so its about time that the media generally and adverts specifically stopped using imagery that suggests that they do. That kind of materialism isn't only bad for the environment, its bad for us, undermining our wellbeing by feeding our sense of insecurity, building even greater dissatisfaction.

And so my first conclusion is that it is crucial for us as individuals, as campaigners, and as politicians, to motivate people to be for something as well as against something. We're very clear about the horrors of climate change, but we also have to paint the picture of what the alternative is, and realise that that alternative can be a positive one.

Martin Luther King had a dream, not a nightmare, and that is what compelled people and drove them forward. I was speaking to Bill Dunstan the other day - he's the architect responsible for BedZed, the Zero-Emission housing development in London. He said that the mark of success for him was not that lots of green people wanted to live there, but actually that ordinary people who don't give a damn about green things wanted to live there too, simply because they're really nice homes. They're beautiful, there's lots of sun, and they're easy to live in. Similarly with public transport, it doesn't have to be the sacrifice that it undoubtedly is today - you don't have to hold your nose when you use public transport in most countries in Europe. Strasbourg is a perfect example, the tram system there is wonderful, and yet I vividly remember being on Oxfordshire County Council and talking about trams, and everyone thinking that we were advocating going back to the Stone Age. So we need to accentuate the positive when it comes to the vision of what we need to see, in order to motivate people to work towards it.

So, in conclusion, I would argue that while the question 'Can Politicians Save Us from Climate Change?' seems to beg a negative answer, because that's where our experience has been to date, it doesn't have to be like that. Can they save us from it? No, but they can be partners with us to do it, and we need action both from the politicians and from citizens as well. Change happens not just through politicians and not just through direct action, but through a combination - that creative, imaginative combination that can push things forward. Alice Walker once said that 'being an activist is the rent we pay for being on the planet'. I really like that, and I think we all owe an awful lot of rent. Let's get moving.

Caroline Lucas MEP is is the Green Party MEP representing the South-East of England.

Climate Outreach Information Network is a charitable trust specialising in public education on climate change and its impacts. COIN works with individuals, households, small community organisations and progressive businesses to directly engage the public about climate change, and supply the means by which they can reduce their own emissions.