"I'm not a plastic bag" reads this week's must-have, a designer tote sold by the not-especially-designer Sainsbury's. All 20,000 were gone within hours, sold at a fiver each to shoppers keen to prove that they could consume as fervently as ever and yet be green too. The limits of such an approach was illustrated by reports that some of the bags were handed over in the conventional sunbed-orange carriers. Buying yet another product to demonstrate one's concern for the environment smacks of self-contradiction. The approach that many companies and consumers take, however, fits the same pattern by participating in various schemes to offset their carbon emissions.

As we report today, the senior scientists on the Intergovernmental Panel on Climate Change (IPCC) are set to conclude that the best way to halt global warming lies above all else in existing technology that can directly cut emissions. President Bush's fantasies of launching giant sunlight-blocking mirrors into space are swiftly despatched as "largely speculative, uncosted and with potential for unknown side effects". Instead, the IPCC is likely to call this Friday for something more prosaic but far more useful: greater energy efficiency in our cars, buildings, power plants and elsewhere. It pinpoints developing countries as the focus for change, arguing that they can leapfrog over the environmentally harmful technologies previously used in the industrialised world. So while Britain has advanced from oil lamps to tungsten lights and is now considering the adoption of greener light-emitting diodes (LEDs), rural India can go straight from kerosene lamps to LEDs. That is the possibility, although even the prospect of greater global warming may not be enough to turn it into reality.

Certainly the threat has had little impact on the way rich countries go about business. Instead of cleaner technologies, the British are largely relying on market mechanisms that allow them to carry on as before. The boom in carbon offsetting, which should really be called carbon outsourcing. The same volume of greenhouse gases are emitted in the same way as before, but are compensated for by some third party - for instance, by buying more efficient stoves for African villages. It is a painless way of contracting out your problem. No wonder, then, that the practice has been (noisily) adopted by so many, from big businesses to politicians to pop stars. The most lasting legacy of defunct Scouse girl group Atomic Kitten will surely be a clump of trees in the Ribble Valley planted in their name to make up for the CO2 emissions from their touring. It is heartening, therefore, when companies announce a green strategy, as Eurostar did this week, in which offsetting is only a last resort. Not only is carbon offsetting a too-easy solution to a profound problem, its mechanics are too often wanting. There is no harmonised standard of practice for voluntary offsets, which means that some of the credits being traded in this £2bn market are of negligible environmental value.

Big publicity and bad practice: this is surely a recipe for popular cynicism, just as the public is taking a real interest in environmental issues. Following the Stern review, the IPCC reports and an increased emphasis from politicians, there is a greater pressure in this country for businesses and government to take action. But the interest could be fleeting. Pollsters at Ipsos Mori point out that back in July 1989, against the backdrop of a benign economy and green speeches by that former chemist Margaret Thatcher, the environment was cited by survey respondents as the most pressing issue facing Britain. It held pole position for all of a month and, by the early 90s, the economy was the only issue in town. This time round it is crucial to build on public concern and turn it into a consensus for real reform. That cannot be done by schemes that, without proper rules, risk looking like little more than wheezes.
© 2007 The Guardian