We buy new clothes all the time – a lot on impulse – filling our wardrobes with stuff we wear rarely, if ever. We buy more food than we can eat, chucking it out when it's no longer fresh so we can buy another lot. Why do we keep buying and buying? Short answer: because we can afford to. Long answer: because, for a host of reasons, we've become addicted to consumption, whether or not it provides lasting satisfaction. We suffer from "affluenza". Many of us engage in "conspicuous consumption" so as to impress other people with our wealth – with how well we're doing in the materialist race. Can't have the neighbours thinking we can't afford the latest model. Other people use their hairstyles or the clothes they wear to express their individuality or, paradoxically, to signal their membership of a particular tribe.

I heard about a partner in a law firm remarking with disapproval that whenever any young person was made a partner they immediately went out and bought a black Volvo. But, someone asked, don't you have a black Volvo yourself? Oh, no, he said, mine's blue. In his new book Curing Affluenza, Richard Denniss, chief economist of The Australia Institute, observes that, these days, much consumption is done for symbolic, signalling reasons, not because we actually need the stuff. And then there's retail therapy – stuff we buy purely for the fleeting thrill we get from buying some new thing. If something's telling you all this needless consumption can't be a good thing, you're not wrong. What's less obvious is why: because of the damage it does to the natural environment. Not only the extra emissions of greenhouse gasses, but also excessive use of natural resources – both non-renewable and renewable, when usage exceeds the rate at which they can be renewed (think fish in the sea).

The richest 15 per cent of the globe's 7.6 billion population can continue living the high life only for as long as we have the wealth to commandeer more and more of the other 85 per cent's share of the world's natural resources. But as the world's poor, led by India and China, succeed in raising their material living standards towards ours, this will get ever harder. It is not physically possible for all the world's population to live the wasteful lives we do. Nothing like all the world's population. How can we stop using more than our fair share of the globe's natural resources? Denniss says we can start by distinguishing between consumerism, which is bad, and materialism, which isn't. Huh? He defines consumerism as the love of buying things, whereas materialism is just the love of things. Meaning the latter is a cure for the former. The more we love and care for the stuff we've already got, repairing it when it breaks, the less we're tempted to buy things we don't need. It's true the capitalist system invests heavily in marketing and advertising to con us into believing we need to buy more and more stuff.

But we're free to resist the system's blandishments. Indeed, I often think the people most successful in the system are those who most resist. Unusually for an economist, Denniss argues that much of what we do – and buy – we do for cultural reasons. Because it's the normal, accepted thing to do. But, just as our grandparents weren't as spendthrift as we are, culture can change. And you need less than a majority of people changing their behaviour to reach the critical mass that prompts most other people to join them and, by doing so, cause an improvement in the culture. If we all stopped buying stuff we don't need, however, wouldn't that cause economic growth to falter and unemployment to shoot up? Yes it would – if that's all we did. The trick is that every dollar we spend helps to create jobs. So we need to keep spending, but we don't need to keep spending wastefully.