Not so long ago I found myself explaining what I meant when speaking of 'food miles' - but that's all changed. The realities of global warming are becoming apparent and forcing us to examine the journeys that create the most carbon emissions. As the transportation of food is one of the main culprits, the term 'food miles' is an accepted part of our vocabulary now.

The frightening thing about all this is that agriculture and food account for nearly 30 per cent of the goods transported on our roads, added to which we are now importing nearly 95 per cent of the fruit and vegetables we consume.

This is not something that we can change overnight, but we can do our bit to reduce carbon emissions by changing the way we shop for food. It used to be considered quite trendy to serve strawberries in the winter and green beans from Kenya throughout the year - we embraced these luxuries with ease. Now people are beginning to question these extravagances and ask what seasonal local fruits and vegetables they can buy instead.

The word 'seasonal' is as important as the word 'local'. It's not going change a thing if we buy locally produced vegetables grown in a greenhouse. The energy needed to heat a greenhouse is significantly more than the energy needed to transport vegetables grown in a hot climate.

Then there's the problem of food labelling. The label may tell us it's British, but how do we know that it hasn't travelled hundreds of miles from farmer to the supermarkets centralised packing sheds, before making a return journey to the district in which it was grown?

It comes down to buying it from a farm box scheme, a pick-your-own, farm shop or farmers' market if we are to make a change. By purchasing fruit and vegetables direct from a farmers' market, we are definitely cutting food miles as these markets only sell food from a defined area, which is usually within a radius of 30 miles.

It is nine years since the first farmers' market opened in Bath. Now there are more than 500 in the UK, providing about 9,000 market days a year which produce an annual combined turnover of some £220m.

Earlier this month, traders and their customers raised their glasses to the first birthday and the continued prosperity of the Shrivenham Farmers' Market, which takes place at the town's Memorial Hall from 3pm to 7.30pm on the first and third Fridays of each month. It's not large but it's certainly popular.

Suzanne Crafter, the market manager, says the success of this vibrant little market, on the Wiltshire-Oxfordshire border, is due, in part, to the fact that it's open on a Friday evening and can cater for those who work during the week.

She also feels they have the balance just right, as between them the traders provide nearly all the basic foodstuffs a shopper requires - eggs, bread, preserves, meat, honey, wine, fruit and vegetables. The fact that several producers have won national awards for their products helps too.

There's an interesting mix of producers at Oxford's latest farmers' market as well. The new East Oxford Farmers' and Community Market was launched in August at the Asian Cultural Centre, in Manzil Way. It opens every Saturday from noon until 3pm and is doing extremely well. It was inspired by the popular farmers' market at Wolvercote, which has proved its worth by specialising in fresh organic produce that's sold every Sunday at the village school from 10am to 1pm. East Oxford market secretary Jessie Marcham said that there was much to be gained by opening every Saturday, as this was the time when most people came out to do their shopping. Opening each week rather than once a month has helped, too, by allowing people to get into a shopping routine.

Opening at the weekend, rather than during the week, is now seen as the way farmers' markets should go if people who work through the week are to be catered for.

Deddington' Farmers' Market, set up in 2001 as the result of a community initiative, opens on the fourth Saturday of every month. Chipping Norton has gone for the third Saturday in every month, which is working well too and the Wantage market, which opens on the last Saturday in the month, is proving to be one of the most vibrant in the county.

The Local Food Group are making their presence felt at farm shops and farmers' markets with a promotional pack they have produced entitled Local Food For Christmas, which retails at £4.50 and provides festive recipes, cooking tips and names of local producers. Farmers' markets are listed, too, along with a guide detailing all the vegetables in season during the next three months.

Tamara Schiopu, the manager of the Berkshire, Buckinghamshire and Milton Keynes and Oxfordshire Food Groups, has produced this guide, which she is confident will promote local food and drink producers at this critical time.

She said: "With all the talk of climate change, now's the time for all of us to do our bit to reduce carbon emissions and buy local food this Christmas. Fresh local food in season is much better for us and for the planet. We don't need to have our food shipped halfway round the world when there is so much available here on our doorsteps."

Another group promoting local food is the National Farmers' Retail & Markets Association (FARMA,) which is currently running a Friends of Local Foods campaign. You will spot the FARMA leaflets detailing their concerns at most outlets selling local produce.

To learn more about the association and become a Friend of Local Foods, go to www.farma.org.uk By becoming a friend you will receive a regular e-newsletter, which includes invitation to food and farming events and an annual guide to farmers' markets, farm shops, pick-your-owns and farmers' box schemes.