Environmentalism is often perceived as promoting a 'back to nature' viewpoint. However, with current population levels there's no way that there can be any realistic return to the agrarian societies of a few centuries ago. On the contrary, true environmentalism has to accomodate peoples needs while having the minimum disrruption to the enviroment, and that implies buildings which get the maximum benefit from a small land area - that is high rise buildings. Hence the exhibition 'Big & Green: Towards Sustainable Architecture in the 21st century' was conceived, to show how large buildings can go together with environmental benefits. This book shows the buildings which were exhibited, together with essays explaining the new ways of thinking.
I have to say that I wasn't entirely convinced that the buildings were doing a great deal to solve environmental problems. For instance my impression is that energy guzzling buildings were only in fashion for a short period of time - I guess around the 1960's. Before that there wasn't energy available to waste, and afterwards there were regulations mandating better efficiency. Hence the energy efficient buildings shown don't seem to be such a great leap forward. Also, the essays are evangelical on the subject of environmentalism, but don't discuss the difficult choices which have to be made in its pursuit. Mostly its a book for architects to show off their new ideas. That said, the book does give a useful summary of current views on how architecture can contribute to environmental improvement, together with visions of what buildings may be like in the future.