Despite three decades of burgeoning eco-awareness, we are still busy creating and consuming, as well as flying and driving, more than ever before. In response to our eco-fears, all we have done, in effect, is to shift our social rhetoric, create new markets for "green" goods and make gestures at recycling. The problem is that the human brain is instinctively resistant to the kind of self-limitation required if we are to save our planetary bacon.
New advances in medical brain-scanning technology are helping to show how the problem lies deep in our ancient primitive wiring. They show, too, how we've built a modern culture that pings these old instincts into a frenzy. Our brains evolved to deal with millennia of scarcity, not today's unprecedented abundance. They dose themselves with reward chemicals when, for example, we see a chance to acquire possessions that might boost our mating status, or encounter foods laden with fat and sugar. When we feel anxious, we get driven by an urge to gather even more possessions.
Our armoury of "want-more" instincts got us through the Stone Age period of famine and threat. We never had to evolve an "enough" button; however, early human civilisation recognised the dangers of our ever-wanting, never-satisfied nature and built social constraints around it. Aristotle, for example, devised the concept of the "golden mean", where the path of contentment lay between the evils of having too little and having too much. Self-constraint was perpetuated in the Middle Ages with the practice of "Christianity writ plain". The Edwardians encapsulated their idea of non-consuming cool in the polite table-saying, "I have had an elegant sufficiency and any more would be superfluous."
Consumer society dumped elegant sufficiency for the doctrine of "more means better": more stuff, more work, more information, more achievement. There is no cachet in declaring "enough". Now we need to return to an appreciating of self-limitation - and not only for the sake of our planetary ecology, but for our personal ecologies. Amid all our abundance, we see more stress, burnout, anxiety and depression, all diseases of affluence.
The concept of "enough" may also enable us to start acknowledging the elephant in the ecological living room: the question of whether we can develop a viable economic alternative to exponential industrial growth. The way the global numbers are stacking up, we may soon hit the point where our planet cannot sustain ceaseless economic expansion by our species. But unless we revive the concept of "enough" as socially admirable, our political leaders will never feel able to broach this great green taboo in any meaningful way.
John Naish's "Enough: Breaking Free from the World of More" is out now, published by Hodder & Stoughton (£16.99)