SCHEMES used by environmentally conscious consumers to cut their “carbon footprint” could take up to a century to deliver the promised benefits, a study has suggested.

Researchers found it takes that length of time for “carbon offsetting” — which often involves the planting of trees in the developing world — to absorb the greenhouse gases emitted by a single flight.

Dozens of fortunes have been made in recent years by entrepreneurs offering people and businesses the chance to neutralise their carbon emissions for a fee.

The new research, carried out by scientists at the Tyndall Centre, based at the University of East Anglia, and Sweden’s Lund University, suggests that such schemes may, in fact, do little more than salve the consciences of those paying for them.

“What we are seeing here is the emergence of a new and completely unregulated financial market,” said Lund’s Professor Stefan Gossling, who led the study.

“These schemes may eventually recapture the carbon people emit now but will only finish the job after most of them have died. That is too long.”

The schemes studied by Gossling included one offered by British Airways to its passengers through Climate Care, a British carbon offsetting company.

It found that an offset bought through the scheme would take about 100 years to recapture the carbon emitted by a flight.

This is because Climate Care includes forestry in its offsetting portfolio, meaning that carbon emitted can be recaptured only as fast as a tree can grow.

The research coincides with a sharp rise in the political temperature over climate change. Last week EU leaders agreed to cut European carbon emissions by 20% from 1990 levels by 2020.

The voluntary carbon offsetting market has sprung from the same global concern over carbon emissions.

There are now dozens of companies charging fees to help people and organisations deal with their carbon emissions. One of the richest is Climate Change Capital, a merchant bank specialising in low-carbon investments, which controls funds of more than £500m and has made millionaires of its founders, James Cameron and Lionel Fretz.

The firm specialises in big industrial projects. Most offsetting companies prefer, however, to support smaller energy-efficiency projects and renewable energy schemes.

A favourite is to buy low-energy lightbulbs for distribution in developing countries. Such schemes can take years to recover the carbon emitted by, say, a flight, but when forestry is the chosen offset mechanism this can stretch into decades.

“When companies offer to offset a single flight over a period of 100 years then the schemes lose credibility,” said Gossling. “How can anyone predict the fate of a forest? A hundred years from now it could burn down and all that carbon would be released.”

Some forestry projects have ended in spectacular failures. Coldplay, the rock group, sponsored 10,000 mango trees in southern India to offset the environmental impact of its 2002 album, A Rush of Blood to the Head.

By last year, however, the trees, supplied by Future Forests, now The CarbonNeutral Company, had withered and died.

Jonathan Shopley, chief executive of The CarbonNeutral Company, said the firm had since moved out of forestry and in to schemes such as wind farms and low-energy lighting. “Any offsets taken out with us in future will recover the relevant carbon emissions within four years,” he said.

The turnover of the CarbonNeutral Company has risen sharply to £4m a year and it has just signed up Silverjet, a new air-line dedicated to business class passengers. It charges an average £999 for a return flight between New York and London — of which £11 goes towards offsetting each passenger’s carbon emissions.

David Wellington, managing director of Climate Care, said: “Many of the criticisms raised over offsetting were valid. This is a young industry and it is still settling down, but the standards are improving very fast. For example, we have already moved out of forestry into renewable energy projects that reduce the time over which offsets take effect.”

But others believe that carbon offsetting is deeply flawed. Dieter Helm, professor of energy policy at Oxford University, said it was little more than a mechanism to allow rich westerners to ease their consciences.

“What we are really doing is paying poor people to reduce their carbon emissions so that we can maintain our luxury lifestyles. If we really want to live sustainably we are going to have to accept the knocks and give up things like flying. In the end they are unsustainable,” he said.

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