Michael McCarthy: Low-carbon consumerism - a new ethical choice

When, as a careful consumer, you read the label on a packet of crisps, what do you look for? How much salt it contains? How many additives, E-numbers, artificial colouring or preservatives? Perhaps you look for all of those.

But consider this. What if the label also told you how much carbon dioxide had been emitted in its manufacture? What if it informed you just what part in causing global warming had been played by the process of putting this snack in your hand? And furthermore, what if a comparison of labels showed you that X Crisps were responsible for fewer emissions of CO2 than Y Crisps? Would it not affect your buying decision - and would not X Crisps get your vote?

This is a new, powerful and radical idea that is just starting to take off - the idea of embedded carbon. How much emitted CO2 is embedded in those crisps, that is, how much was involved in making them? How much in that instant chicken tikka you're having for dinner, or that sofa you covet, or those new trainers you want to buy? This is not fanciful - it can be calculated. Indeed, the Carbon Trust has been calculating it with Walker's Crisps.

When it is calculated more widely, the embedded carbon in a retail product may become as big a turn-off as artificial sweeteners. High carbon content may get the same thumbs-down from careful consumers as high salt.

You doubt it? Well. the first stirrings of this quite remarkable trend - to view carbon in the retail sector as a pariah material, socially - are already visible. Sales of 4x4 cars, desperately trendy until only very recently, are now falling through the floor. That has been prompted by widespread feelings that the amount of fuel they use, and thus the amount of greenhouse gases they emit, are quite obviously egregious, and unnecessary, even to live a busy family life with children to be taken to school in London or other major cities. The 4x4 is becoming socially unacceptable because of its carbon.

But the 4x4 is indeed obvious. The Carbon Trust's breakdown of the UK's carbon footprint into consumer sectors shows just how far the idea can be taken. Virtually everything we wear, sit on, clean with, heat with or eat contains embedded carbon - which can be reduced if the manufacturing companies concerned try hard enough. And, of course, the companies get a powerful incentive to try, they are looking at a high street marketing advantage.

Hitherto we have tended to look at the great heavy industries, especially energy generation and manufacturing, as the places where we must seek to make our greenhouse gas emissions cuts. That is natural, because they are the biggest single emitters.

But when the traditional view of CO2 emissions is turned on its head, and the emissions are reallocated to the point of consumption rather than the point of manufacture, we can see just how much a part we as individuals could play in cutting emissions by the purchasing choices we make.

It just goes to prove the truth of a couple of sayings that the environmental movement has always held dear. The first is, The Personal is Political. And the second is, Think Globally, Act Locally.

Believe it or not, that may become an appropriate way to view your future purchases of Cheese 'n' Onion (or Smoky Bacon, for that matter).