Dominic Kennedy

Walking does more than driving to cause global warming, a leading environmentalist has calculated.

Food production is now so energy-intensive that more carbon is emitted providing a person with enough calories to walk to the shops than a car would emit over the same distance. The climate could benefit if people avoided exercise, ate less and became couch potatoes. Provided, of course, they remembered to switch off the TV rather than leaving it on standby.

The sums were done by Chris Goodall, campaigning author of How to Live a Low-Carbon Life, based on the greenhouse gases created by intensive beef production. Driving a typical UK car for 3 miles [4.8km] adds about 0.9 kg [2lb] of CO2 to the atmosphere, he said, a calculation based on the Governments official fuel emission figures. If you walked instead, it would use about 180 calories. You'd need about 100g of beef to replace those calories, resulting in 3.6kg of emissions, or four times as much as driving.

The troubling fact is that taking a lot of exercise and then eating a bit more food is not good for the global atmosphere. Eating less and driving to save energy would be better.

Mr Goodall, Green Party parliamentary candidate for Oxford West & Abingdon, is the latest serious thinker to turn popular myths about the environment on their head.

Catching a diesel train is now twice as polluting as travelling by car for an average family, the Rail Safety and Standards Board admitted recently. Paper bags are worse for the environment than plastic because of the extra energy needed to manufacture and transport them, the Government says.

Fresh research published in New Scientist last month suggested that 1kg of meat cost the Earth 36kg in global warming gases. The figure was based on Japanese methods of industrial beef production but Mr Goodall says that farming techniques are similar throughout the West.

What if, instead of beef, the walker drank a glass of milk The average person would need to drink 420ml three quarters of a pint to recover the calories used in the walk. Modern dairy farming emits the equivalent of 1.2kg of CO2 to produce the milk, still more pollution than the car journey.

Cattle farming is notorious for its perceived damage to the environment, based on what scientists politely call methane production from cows. The gas, released during the digestive process, is 21 times more harmful than CO2 . Organic beef is the most damaging because organic cattle emit more methane.

Michael OLeary, boss of the budget airline Ryanair, has been widely derided after he was reported to have said that global warming could be solved by massacring the worlds cattle. The way he is running around telling people they should shoot cows, Lawrence Hunt, head of Silverjet, another budget airline, told the Commons Environmental Audit Committee. I do not think you can really have debates with somebody with that mentality.

But according to Mr Goodall, Mr OLeary may have a point. Food is more important [to Britain's greenhouse emissions] than aircraft but there is no publicity, he said. Associated British Foods isn't being questioned by MPs about energy.

We need to become accustomed to the idea that our food production systems are equally damaging. As the man from Ryanair says, cows generate more emissions than aircraft. Unfortunately, perhaps, he is right. Of course, this doesnt mean we should always choose to use air or car travel instead of walking. It means we need urgently to work out how to reduce the greenhouse gas intensity of our foodstuffs.

Simply cutting out beef, or even meat, however, would be too modest a change. The food industry is estimated to be responsible for a sixth of an individuals carbon emissions, and Britain may be the worst culprit.

This is not just about flying your beans from Kenya in the winter, Mr Goodall said. The whole system is stuffed with energy and nitrous oxide emissions. The UK is probably the worst country in the world for this.

We have industrialised our food production. We use an enormous amount of processed food, like ready meals, compared to most countries. Three quarters of supermarkets energy is to refrigerate and freeze food prepared elsewhere.

A chilled ready meal is a perfect example of where the energy is wasted. You make the meal, then use an enormous amount of energy to chill it and keep it chilled through warehousing and storage.

The ideal diet would consist of cereals and pulses. This is a route which virtually nobody, apart from a vegan, is going to follow, Mr Goodall said. But there are other ways to reduce the carbon footprint. Dont buy anything from the supermarket, Mr Goodall said, or anything that's travelled too far. dkennedy@thetimes.co.uk

Shattering the great green myths

Traditional nappies are as bad as disposables, a study by the Environment Agency found. While throwaway nappies make up 0.1 per cent of landfill waste, the cloth variety are a waste of energy, clean water and detergent

Paper bags cause more global warming than plastic. They need much more space to store so require extra energy to transport them from manufacturers to shops

Diesel trains in rural Britain are more polluting than 4x4 vehicles. Douglas Alexander, when Transport Secretary, said: If ten or fewer people travel in a Sprinter [train], it would be less environmentally damaging to give them each a Land Rover Freelander and tell them to drive

Burning wood for fuel is better for the environment than recycling it, the Department for Environment, Food and Rural Affairs discovered

Organic dairy cows are worse for the climate. They produce less milk so their methane emissions per liter are higher

Someone who installs a green light bulb undoes a years worth of energy-saving by buying two bags of imported veg, as so much carbon is wasted flying the food to Britain

Trees, regarded as shields against global warming because they absorb carbon, were found by German scientists to be major producers of methane, a much more harmful greenhouse gas

Sources: Defra; How to Live a Low-Carbon Life, by Chris Goodall; Absorbent Hygiene Products Manufacturers Association; The Times; BBC