My daughter faces a dilemma.  Should she take advantage of the present scrappage scheme to trade in the old van that she and her circus artist partner have used for the last few years - and in which they have travelled the length and breadth of Europe - for something that is new and greener?

She has always been of an ecological persuasion, even campaigning on crutches for some green purpose, six weeks after a major road accident.  It was a long time before she bought a car at all and she still winces whenever she fills it up with fuel.

The problem is - as she never ceases to tell me - that with the miles they do in the van it will take a large number of years to save enough energy to make up for the carbon cost of manufacturing a new vehicle.

I had something of a similar problem the other day: I had an old refrigerator which undoubtedly was less efficient than a modern machine. Refrigerators don’t use much energy so how could I know that buying a new one would actually save enough to make up for the carbon load incurred in making it?

I mean think of all the steel - iron ore mined and smelted and rolled and coated, ditto the plastics and the motor (think energy-intensive copper or aluminium smelting) before we even get to the factory where the refrigerator (or the car) is made.  And then there is the energy cost of making the machines that make the steel and cut and press it into the required shapes.

Yet when you ask people what carbon costs have been incurred in manufacturing a product most simply don’t know.  I suppose it depends how you do your sums.  But I wonder if the authorities are not missing a trick here.

We are extolled from every quarter to change our carbon-wasteful behaviours.  Campaigns such as 10:10 ask us to pledge to reduce our emissions by 10 per cent in 2010.  ‘Think green!’ is the message from every billboard.  Save energy and save the planet from climate change!

But if we are going to move towards behaviours that are greener and have less of a planetary impact then surely one part of this must be to highlight the energy we spend - or rather the emissions created - when we choose to buy product ‘x’ over product ‘y.’  

This is not just a question of whether the product uses energy efficiently - whether it qualifies for an Energy Star sticker for instance - but whether the manufacture of the product itself is emission friendly.

At present, we the public have very little information as to what is good and what is bad.  Articles we read in magazines tell us not to buy food with a high air miles content - beans from Africa, for instance - or plastic toys from Asia.  But are these significant in the general scheme of things?

When you consider many packs of beans you can put on an aeroplane - or how light the plastic toy is and how many such toys you can carry in a great container ship - you start to think that had you walked to the supermarket, instead of making a short journey in your car, you might be eating air freighted beans every day of the year and still make a carbon saving.

That is you might, if there was any easy way of knowing just what emission load these products carried or some labelling scheme that allowed you to compare the inherent emissions cost of various products.

While you were in the supermarket you might well have found yourself visiting the chiller cabinet or the deep freeze and buying a joint of beef and perhaps a leg of lamb for the weekend.  You would have passed by the air freighted beans with a smug too-many-airmails smile and instead you are now filling your trolley with meat.

Nowhere, however, will it say what emission load that meat carries.  It is by no means certain that the label will even tell you whether the meat comes from naturally grass fed animals, or whether your beef has been fattened up with oils and cereals grown on land that was once virgin forest.

Neither will it tell you the emission cost of the transport, the refrigeration and the packaging of the beef or how much of the animal will be thrown away before your joint goes into the oven (more emissions in the cooking).  And then there is of course the vast amount of methane - each animal in emission terms has more effect in a year on climate than a car - that the cow or sheep produces as a result of its own digestion.

So what is needed is some simple system of product labelling that is as applicable to cars and refrigerators as to plastic toys and joints of beef.  Something that will tell us - approximately - what carbon emission equivalents have been generated in bringing this product to the retail outlet.

So here is my suggestion: Little Green Trees!  Stickers that can be placed on products that indicate their level of ‘emission load.’  Let’s say that one Tree would represent 100 kilograms of CO2 emissions. Roughly the amount of CO2 that a mature tree can absorb in a year. So the fuel used by an average car during a year would represent 30 ‘Trees.’   

Clearly a unit of that size wouldn’t be of any use when it comes to judging toys, or joints of meat.  So we would need subsidiary units, let’s call them, Branches and Twigs such that 100 ‘Branches’ (each worth 1 kilogram of CO2 equivalent emissions) made up one ‘Tree’ and 100 ‘Twigs’ - each worth 10 grams of CO2 - made up one ‘Branch.’  

As a practical example, the fuel to take a car one kilometre would be approximately 15 ‘Twigs.’

Such a labelling system could be voluntary.  It would encourage manufacturers and food suppliers to ‘green’ their products.  Moreover, it would have the advantage of being a simple and easy graphic.  Two and a half trees - little brown trunks with green tops - is more comprehensible and visually striking than a label that says 250 kilograms of CO2.

So there you have it.  A visual reminder of the emissions you are causing every time you go shopping or fill up your car or buy an airline ticket (Atlantic crossing - 25 ‘Trees’).  If you buy beans perhaps - even air freighted ones, or that little light plastic toy - the label might say with a yellow smiley. ‘Emissions generated in bringing you this product were less that one ‘Twig’ (100 grams of CO2 equivalent).’

My daughter might then know - in Trees, Twigs and Branches - whether she really should buy that new fuel efficient car.