Rebecca Tyrrel: Stuck in a traffic jam and I've got the carbon emission blues

I wondered how much of my life it would be possible to offset

Just how much of my life, I wondered bleakly, as I whiled away half an hour in a high-pollution, London traffic jam on Hammersmith Bridge last week, would it be possible for me to offset? I was, of course thinking of the way Mr Tony Blair so deftly dealt with any qualms he might have had over his Bee Gee-bound, Christmas holiday flight. What, in fact, the Prime Minister appears to have done is pay someone else to plant some trees to make up for the aeroplane's carbon emissions. This is a fabulous way to assuage middle-class guilt about high consumption, I thought, as I sat there in my Audi estate, turning the heater high and causing the petrol gauge to leap about with about as much excitement as a No 10 spokesperson who has just discovered that such a politically handy thing as offsetting exists.

So you can make a phone call, send off a relatively small amount of money - £20 or so per transatlantic flight - and travel with a clear conscience to the house of a pop star that hardly anyone's granny still listens to. And when you are not doing that you can run your children to and from their private, fee-paying schools - I'll get to Ruth Kelly in a minute - and get stuck in traffic jams in the process, without any guilt.

To undo the damage done by my daily school runs, my trips to Pilates classes and a decent butcher, I reckon only two dozen or so trees per year would have to be planted in Dorset. (I say Dorset specifically because a forest the size of this county would have to be created annually in order to deal with the UK's annual CO ^₂ emissions. This is according to a leading, official, offset expert - yes, these people do exist and what a brilliant bandwagon that is to have jumped upon.) I have family members in Dorset who say they wouldn't have a problem with living in a forest as long as there was eco-friendly signage so they could find their houses. My thoughts moved on to that other cause of crippling middle-class guilt: the private education versus state education question, the journey to my son's school being the very reason for my car's inclusion in this traffic jam.

It didn't take last week's Kelly controversy - the removal of her son from a state school to a handsome private one, to remind me how revoltingly middle-class and socially deviant my own child's education is. Instead of going to a state school within walking distance, he attends one five miles away that costs more than £15,000 a year, looks like a stately home and stands amid grounds large enough to be sequestered for major reforestation. Clearly there is some offsetting to be done. Kelly has more than one child, so the obvious thing for her to do is trade one against the other - one state- educated offspring for one privately educated one.

My single option, as the parent of an only child, would be to compensate by ceasing to pay for my other dependents - my dogs - to be walked privately. But that would only work if there were such a thing as a subsidised dog walker that I could send my animals to. But there isn't, although there should be with the proliferation of bull terrier-type dogs on our streets. If we destroyed all dogs we would be cutting down on methane emissions. I could do my bit by appointing myself dog-death warden. But I'd feel a burden of guilt for all those little animal deaths - farts or no farts.

So, my guilt cannot be easily assuaged. Suddenly I felt like George Bailey in It's a Wonderful Life, deciding whether to just give up and end it all. It was lucky the traffic moved on when it did - otherwise the Thames, flowing coldly and greyly a hundred feet beneath me, was beckoning.