The impending extinction of tigers, the melting icecaps and the ravaging of the rainforests are symptoms of an emerging global crisis. A new World Wildlife Fund report out maps its scale and concludes that if we don't change course by 2030, we will need a second Earth to meet our needs.

But does all this ring true? After all, in the UK we are greener than ever. Our air quality has improved dramatically – "pea soup" killer smog has been consigned to the history books. We have cleaned up power stations and banned ozone-destroying chemicals. We have nature reserves and some of our most polluted rivers have enjoyed a dramatic renaissance. We are planting more trees and many toxic pesticides have been banned. We have even made progress in improving household recycling rates. So what is the problem?

Part of the trouble is that we have simply exported a lot of the environmental damage we cause. In the age of globalisation, we can live greener here because we have sent the pollution and habitat destruction somewhere else. For the past few years, it has become fashionable to close down conversations about what we need to do to protect the environment by asking: "What about China?", the implication being that China is causing such vast environmental impact as to render our efforts pointless.

There is no doubt that China's footprint, and those of several other fast developing economies, has increased hugely and in a short time. But a lot of the pollution and environmental damage is being done in order to supply us, and other western countries, with consumer goods, chemicals, ships, steel and other modern essentials. The point is underlined by the fact that Denmark, to many eyes a "green" country, comes out in the WWF report as third in a world league table of the highest impact countries. Like us, they look greener because they have exported their environmental problems elsewhere.

There is a harsh reality behind all this that people everywhere, and in the west in particular, need to get their collective minds around. It is the fact that the Earth is finite and that our current patterns of consumption and waste generation are overwhelming its ability to cope. We are confronted with a choice: either change how we live or face grave consequences arising from a kind of ecological credit crunch.

The emerging crisis has three main parts. The first relates to the vast quantities of greenhouse gases we are releasing. We need to cut these by about four-fifths in the next 40 years or so, starting now. If we don't, the impact of climate change and ocean acidification might lead to massive economic damage. The second crisis is linked to the loss of nature – animals, plants, ecosystems, and all the things they do for us, caused by habitat clearance and farm pollution. On top of this is a third crisis of rapid resource depletion. Fisheries, oil reserves, fresh water and soil are among key assets now facing planet-wide depletion.

Projections on how these different aspects map out under business-as-usual scenarios later in the 21st century do not paint a pretty picture, especially when one considers the vast momentum added by population increase and the effects of economic growth. There will be more people and they will be richer, with more cars and flights, demanding more products and eating more meat. There are 200,000 more of us each day and the vast majority want to live more like most Europeans and Americans than most Africans. If the developing world takes on our lifestyle, where will it export its environmental problems?

So much for the problem; what is the solution? Technology is vital, but will not be enough on its own. There is a need for culture change and to look hard at how we measure economic progress. At the moment, we judge success basically in terms of how much economic growth we can achieve, which in turn is often a proxy for how much stuff we are using up. It's a big challenge, but then it is a big problem. By doing small things, we will get only small improvements and small improvements will still lead to disaster.

We need leadership for big change from all quarters and we need it fast. And we especially need leadership from the richer and better-off countries to show how it really is possible to do things differently. There is no point telling China it is behaving badly while continuing to import its pollution. That will take us nowhere.

Tomorrow, governments will again gather for another of their crucial environmental summits. This time it is in Japan and is about biodiversity. Having failed to meet earlier targets to cut the rate of biodiversity loss, it is to be hoped that they will set new ones. But if these are to be met, then the changes agreed must go far beyond how many national parks we can designate. When natural resources really start to get scarce, such lines on maps will be worthless as a final scramble for the Earth's resources gets underway. If there is to be salvation from the eco-crunch, then deeper change is required.

Some gloomily conclude that the impending collision of the big environmental crunches is part of humanity's natural destiny. Like a global analogue of Easter Island, we will simply use up all the resources and degrade the environment until collapse becomes inevitable. Many of us take a different view, however, pointing to humans' unique ability to co-operate and to use inventiveness to overcome the most challenging problems.

The response to the eco-crunch is not only about stopping things we like doing. There is huge energy going into how a greener economy could work. Part of it is about creating jobs in the cutting-edge clean technologies of the future. Social scientists are also beginning to better understand how the human psychology that so readily lends itself to consumerism might be harnessed instead for sustainability. It can be done.

There is, however, a danger that the size of the task can create paralysis and we end up doing nothing. But in thinking big and seeking major change there is nothing to be lost, only to be gained. And we must all be part of the solution, because this is everyone's job, not just governments. Culture can change from the bottom up and all of us can be leaders. For our children's sake, we really do need to promise the Earth and to start living like we mean it. What else do we have to offer the future? I don't think too many history books will praise us for continuing with business as usual.

Harmony by HRH the Prince of Wales, Tony Juniper and Ian Skelly is published by Harper Collins