MOST of us are aware that if we burned coal, drove a petrol or diesel car or flew on holiday we would produce carbon dioxide and methane, so ensuring the climate will change markedly this century. However I suspect few will understand the damage caused by buying products it would have been cheaper to make at home – like sandwiches.

In the past I have pointed out that the emissions from a cheese or beef butty clearly involve the CO2 produced by growing the wheat, using milk to make the butter and cheese, plus that from the methane associated with a cow’s four stomachs.

However an important additional factor is where the sandwich originates – in our kitchens it’s better, but from a supermarket shelf it’s worse because of the larger volume of climate change gases involved.

It may well be that the principle of making food at home rather than buying it ready made is a general one because of the transport, refrigeration, the cardboard and plastic packing, and the way that much food is dumped because of the best by date when normally it’s still edible.

Annually sandwich making produces over ten million tonnes of CO2, with most of it arising from those sold in shops, particularly if they involve beef because of the methane from all those stomachs. A home made ham or cheese sandwich only involves 620 grams of CO2, the equivalent of driving five miles, while a shop bought one is 1,350 grams, and 12 miles in the car.

Making each of the top ten shop sandwiches produces over 1,000 grams of CO2, that is they are responsible for one litre plus of CO2, and it doesn’t say that on the supermarket shelves. Nor does it mention that refrigeration produces a quarter of the CO2 and the packaging another tenth.

So it’s homemade sandwiches from now on.