Carbon offsetting is an infant industry that has made huge claims in order to establish itself. It is rooted in an assumption, which is still contestable, that the vast majority of the global warming since the late 19th century is due to man-made activity and, furthermore, that damage to the atmosphere can be cancelled by virtuous intervention. As late as 2005, almost no one chose to both pay for their air fare and then reach into their bank account again to contribute to schemes that would “pay” for their indulgence. Today, by contrast, a rapidly increasing number are ready to make that sacrifice.

Whether their honourable intentions are being rewarded as they might expect is debatable. For as we report today, the decisions made by the leading company in this sector, Climate Care, are open to legitimate criticism. One of the main offset plans pioneered by this company involves funding Indians to use “treadle pumps” rather than their diesel alternatives in agriculture. Most of those farmers would be too poor to use the mechanised alternative and in any case they would need to operate their pumps for two hours a day for at least three years to offset one return flight from Britain to India. Such implausible initiatives have not prevented the likes of David Cameron insisting publicly that their flights to the sub-continent were carbon neutral.

This is not the only example that stretches credulity. Other highly publicised offsetting proposals in Central America and South Africa are also vulnerable to the charge that they are either subsidising moves that would have occurred anyway or delivering far less than implicitly promised or, perhaps most damning of all, are bribing those in the Third World to engage in functions that will retard rather than enable them and their countries to join the developed and wealthier world.

In fairness, if there were schemes that did instantly offset air travel or other supposed sins Climate Care and other companies would certainly direct resources at them. The blunt truth is that the sort of quicky offsetting that salves the conscience of socially concerned tourists does not grow on trees. They might instead rely on trees, which take an awfully long time to grow and whose positive environmental impact (which does exist) is very difficult to estimate with the sort of pleasing precision that makes their customers feel satisfied. Like so much else related to climate change, much of what is declared to be science relies on faith.

It may make more sense for those who would like to offset part of their carbon emissions to look elsewhere. They might invest in particular projects in which, through their own research, they have confidence; or they might conclude that an old-fashioned donation to an established Third World charity was a better bet, even if the environmental benefits were not related directly to offsetting the carbon emissions.

If those who wish to be at the forefront of offsetting wish to avoid that fate then they will have to change the way that they do business. The rules by which old “dirty” companies have to live apply to them too. They include absolute transparency and compelling evidence that the claims made on behalf of a company are realised in practice. If not, the ultimate test of any market - the customers - may opt to offset them.