We live at a critical moment in history. Our actions over the next 30 years will define whether humans are a successful or unsuccessful species, and we will be ill judged by the future if we don’t take bold steps now.

By 2050 we must have cut carbon emissions by 80 per cent. This will need a social and technological change within the lifetime of today’s children equivalent to the leap from the beginning to the middle of the Industrial Revolution.

Yet most of the world has not bought into the need for this scale of change. People behave as though faced with lifestyle choices, rather than fundamental decisions about the way we live.

The environmental movement has created an awareness that societies around the world are profligate with resources and not living with the grain of nature. But today’s challenge for environmentalists is to realise that idealism alone cannot deliver solutions on the scale and in the time frame we need.

My dear friend Richard Sandbrook, who set up Friends of the Earth with Jonathon Porritt, gave me this understanding. He left the NGO movement because he felt the world’s problems were too critical to be left to idealists without a sense of how practically to resolve them.

The trouble is that environment- alists are, quite rightly, trying to be a critical friend of big business, without understanding that there are lots of people in business who think as they do. By not realising this, they are wasting the chance to change the world quickly.

My view profoundly shifted when we built the Eden Project in the late 1990s. We worked closely with big contractors and observed the pleasure they took in contributing to the environmental debate. We saw how efficient these top professional people were at delivering things on a scale we could never achieve. Short of turning all the lights out and having a Luddite regression, the only way I believe we can change the world quickly is for doubters to get involved with big business, and change its focus.

In that sense we, at Eden, have got our hands dirty. Our first partner was Rio Tinto. Our relationship with it began in 2002 when Richard Sandbrook started working with Eden. Eden is the ultimate symbol of the regeneration of a mining project, so we were in a great position to talk to the big mining companies.

Rio Tinto has made significant environmental strides because, first, it’s good for business and its brand and second, because the people who work there want to be proud of their legacy. That is about more than profits.

This is an attitude that is starting to influence people in terms of the jobs they choose. Companies need to change, not to produce good corporate responsibility reports, but because good people tend to have good ethics and can work wherever they like. Woe betide the company that doesn’t see this.

One of our next partners was equally surprising: EDF Energy. We bought our green tariff electricity from EDF, which led to discussions about an education project. The energy provider sponsored a big array of solar cells that give us about 30 per cent of the power we need for our education building.

The more we spoke to EDF, the more we became aware of its ambition to be a clean energy giant. Not just for altruistic reasons, but because EDF genuinely believed in the vision of a low-carbon world.

The company could see that the future might lie in new energy technologies and managing energy supplies to communities, rather than charging for energy use. This idea formed the basis for a new business model, but that model required the support of both the Government and wider society. A Rubicon had to be crossed, the company realised, which involved serious social change.

New technology and new government policies would follow on from that desire for change — that was the crucial point. Whole communities would need to look after their waste and obtain energy differently. It wasn’t just about individual actions such as turning lights off and flying less.

Our ambition was to create a moment of collective awareness, when everyone learns for themselves what it’s like to be a bit greener. Once the population has bought into a greener culture, government must step in to move things on.

We were planning an event called The Big Lunch on July 19 to improve neighbourliness by encouraging people to have lunch in the street. EDF Energy had a similar idea: Green Britain Day.

Green Britain Day is about small cultural changes that people are happy to make, but that collectively make a big difference. If everyone turned their computer off for one day, they’d get some idea of the control we have over our resources. We are not just flotsam and jetsam tossed about on waves beyond our control.

If everyone cut their consumption by 20 per cent and saw the results, they would be amazed to find how easy it was, and want to go the rest of the way. That’s why it’s important we all start to do it together.

Green Britain Day, which takes place tomorrow, is merely a kick-start. It’s like a metaphorical New Year’s Day to give people the chance to say, “OK, it’s just one day; we’ll turn our lights off.” Once people have done it one day, they think, why not do it every day?

If Britain cannot seize this opportunity for cultural change, we will end up dependent on others for our energy and technology. It is outrageous that a nation long famous for scientific invention is dithering about investing in the next generation of technologies.

Mark Twain said reasonable men bend themselves to the ways of the world, therefore it stands to reason that only unreasonable people can change it. From tomorrow, let us all be collectively unreasonable.

Tim Smit is chief executive of the Eden Project in Cornwall

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