We've come to the historic city of Siena to seek the answer to a very modern dilemma - is our way of life sustainable and, if not, how can we change?

Professor Enzo Tiezzi is one of the pioneers of the concept of sustainability.

For 25 years he has been telling us that our relentless pursuit of growth will result in society's downfall.

In scientific papers, international lectures and more than 20 books he has argued for a new industrial and economic model.

We simply cannot continue to deplete the planet's resources as we have done. Nature, he says, will not allow it.

But the world took little notice until climate change, dwindling energy resources and an economic crisis forced us to listen.

Now, says Professor Tiezzi, it's a matter of urgency because time has run out.

EURONEWS

"How long can we continue the path we've been on now for more than a century?"

PROFESSOR ENZO TIEZZI

"I think that this period is ended, completely ended and it's necessary to change yesterday. The point is very simple: before we were living in an empty world full of resources. Now we are living in very full world with 6 billion people and resources are going down. So it's necessary to pass to a sustainable way of life. Sustainability is not based on growth, it's based on development. Development means quality not quantity. Growth means only quantity."

EURONEWS

"If we need a new economic model, can you propose one?"

PROFESSOR ENZO TIEZZI

"I really believe that the new model must be based on the general laws of nature. The laws of thermodynamics, for instance, the famous first and second principles are laws of nature. Of course, now there is a new actor. Before the actor was only political, cultural and so on. Now the problem is that the new actor is nature. You cannot joke with nature and the role of science is very important because the proper use of science is not to conquer nature, but to live with nature."

EURONEWS

"At the moment we get 85% of our energy from fossil fuels and it's causing climate change and also fossil fuels are dwindling. Are we going to be able to replace them?"

PROFESSOR ENZO TIEZZI

"This is a very difficult and important question. I think there is a period of about 100 years of passage. And during this period we will continue to use oil, but less and less and use methane. And then you have to develop seven, ten different energies. But you have to do this now. Photovoltaic, wind energy, biofuels, bioethanol, geothermal energy, hydro energy and everything is connected through the natural cycles. And also we must use thermodynamics to reduce consumption of energy. This is a new source of energy."

EURONEWS

"What happens if we don't change?"

PROFESSOR ENZO TIEZZI

"I would say if you don't change everyone is going to die. But I am not pessimistic and I don't think that in this beautiful planet and in this very beautiful history of life, of biological evolution there is the possibility of such a type of destruction. We may have terrible wars, for instance, for water in the future, terrible wars because there are too many people on the planet, terrible wars over energy. But finally I think that good things and beautiful things will have the possibility of winning. In the past, only growth was important, economics and social issues. Now we need ethics and aesthetics. We need beauty, we need common good. We need to be good and to be beautiful as much as possible."