If you want to be green - kill a cow Stop, stop. I can feel the guilt building up already. I can feel the self-loathing welling in my skull, the horror at my appallingly affluent consumerist lifestyle. In just a few short months, I will be taking the whole family off on holiday again, and once again our plane will contribute to the cat's cradle of CO2 that is swaddling the globe. Out of the nozzles of the Rolls-Royce turbo jets the lethal vapours will spew into the defenceless stratosphere, and, far beneath us, a startled look will pass over the features of another poor polar bear as he plops through the deliquescing floes. I must atone! I must make a sacrifice! I must offset my emissions and appease the great irascible Sun-god as he prepares to griddle us all. I had heard somewhere that you could be "carbon-neutral" by planting trees before you fly. That's right. Shove in a few poplars, I was told, and bingo, you can feel all good about your skiing holiday or your winter break in Tunisia. So I dialled up the eco-websites and -- what's this? It turns out they have got it all wrong! Guilt-stricken Western holidaymakers and others have so far paid £300 million to have trees planted in their name by carbon offset companies, and the whole thing turns out to be a complete nonsense. It now appears the scientists think the trees just make things worse. Far from soaking up your share of CO2, most trees in non-tropical areas are thought to trap heat and thereby increase global warming. Aaaargh! Bad trees! Killer trees! But what can I do to exculpate my sin? Here I am, a caring, modern, green politician, proposing some time before the end of this year to take about six people in a plane for no better purpose than simple recreation. Like Tony Blair, I must deal with the hate and rage of the new green puritans; and also, it goes without saying, I genuinely want to make amends for any damage I am doing. So I have done my homework, and I have come up with a far more effective solution. As ever, I have consulted the ancient texts, and have been reminded that the Greeks and Romans were also convinced of the importance of making a sacrifice before any tricky voyage. You will recall that the Greek task force for Troy actually killed Iphigenia, daughter of Agamemnon, in the hope of guaranteeing good sailing weather -- with bad consequences for Agamemnon's conjugal relations. Now we are only taking a family holiday, and I don't think Zeus or Jupiter would desire anything so extreme. A single cow would be about right. If I were an ancient Roman setting out on a family holiday, I would get some old milker and do her up as if for a party. She'd have her hair washed and combed and cut, and there would be ribbons and purple woollen fillets about her horns. Then my chums and I would decently cover our heads and we'd drone loads of stuff in Latin and chuck some sacred meal about the place; and then one of us would hold a handful of food under the poor old girl's nose, and as she bent her head to snuffle it up we would take this -- praise be! -- as a sign that she had assented to her death, and at that auspicious moment she would be whopped hard on the side of the head and her throat would be cut; and then Jupiter would nod, and Olympus would tremble, and the whole family would be able to go off on holidays with a clear conscience. And the funny thing is that, if we wanted to pay our debt to the great green earth-goddess Gaia, and neutralise the ill-effects of going up in a plane, then, as far as I can see, killing a cow is still exactly the right thing to do, two thousand years later. I mean it. There are 1.3 billion cows on this planet, and every year each cow produces about 90kg of methane, and as greenhouse gases go, methane is about 24 times worse than CO2 in sealing the heat in the air. According to a recent report by the UN's Food and Agriculture Organisation, agriculture produces 18 per cent of the world's greenhouse gases, as measured in CO2 equivalent -- and that, my friends, is more than is produced by the entire human transport industry. Think of it: for every cow you killed, you would be ridding the world of 90kg of methane a year -- easily enough, surely, to justify an Easyjet flight. Now it may be that you are repelled by the idea of killing a cow, and you may think that the poor farmers will only be driven to breed a new one to replace it. But there are still plenty of other things you could do that would make more sense than planting trees with these carbon offset companies. You could make sure that your house was properly insulated. You could turn down the central heating and wear more sweaters; and if you really wanted to tackle global CO2 emissions, you would campaign for nuclear energy, since power production is responsible for 24 per cent of global emissions. Or better still you could help do something to stop Third World countries from burning the forests, which produces 18 per cent of CO2. But, of course, people aren't interested in these kinds of facts. They want the religion. They want the sweet moralistic feeling of telling someone to stop doing something. They want to be able to rage about Chelsea Tractors and Tony Blair's flights, and they want to give vent to their feelings of disgust at the whole triumph of Western consumerist capitalism; and what worries me is that, in the end, the moralising mumbo-jumbo becomes more important than the scientific reality. We face huge decisions, such as whether or not to allow scientists to use human genetic material in animal cells; and I want those decisions taken on the basis of whether or not the advance can help cure disease, not on the basis of "Frankenbunny" headlines. We should cease our pagan yammering for sacrifice, and look at what the science really demands. It is a sign of our terrifying ignorance that so many would still prefer to plant a heat-producing tree than see the wisdom of the ancients, and kill a flatulent cow.