Carbon offsetting companies came in for a drubbing in January when the government announced that only four of the UK’s 59 schemes met its standards. The Department for Food and Rural Affairs (Defra) is working on a ‘quality mark’ that it hopes in the future will separate out the good guys from the greenwash, but while many offsetting schemes are working to bring themselves into line with Defra’s code of practice, the standard won’t be available until the autumn. Here I take a look at some of the UK’s leading offsetting schemes to see how they compare.

The idea of offsetting schemes is to enable travellers to calculate their carbon dioxide emissions and then buy equivalent credits from emission reduction projects, which will in turn reduce the emission of an equivalent amount of carbon dioxide - usually through investing in renewable energy schemes and reforestation projects. Some schemes focus just on emissions caused by flights – the fastest growing contributor to global warming - while others work out emissions from specific train, car and ferry journeys to enable travellers to offset their journeys whatever mode of transport used.

Carbon offsetting might sound like a scientific procedure, but I found the figures quoted by the five companies varied widely, both terms of how much carbon they say is emitted and how much they suggest customers pay to offset.

The amount of carbon emitted for a return flight London-Sydney varied from 3.7 tonnes to 5.61 tonnes and a return car journey from London-Edinburgh from 160kg and 250kg.

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The difference is due to the variation in how the schemes take into account the type of aircraft or car, fuel efficiency, the estimated number of passengers and the speed of travel. All the offsetting schemes do, however, agree that flying and driving are more polluting than train travel, which is charged between a quarter and a third of the amount it costs to offset flying the same distance (though Eurostar says that travelling on its trains between London, Paris and Brussels generates as little as ten times less carbon dioxide than flying the same routes).

Car travel, mile for mile, costs about the same amount to offset as flying. However, Mike Rigby of Co2balance.com says his company is about to restructure its figures to reflect the fact that the carbon emitted at higher altitude has almost twice the effect it has on the ground. He also says his company will be charging 10 per cent less for people in economy class because he says they take up less space than business or first class.

The cost to offset varies too, depending on the type of project supported and how much administration goes into supporting it. The CarbonNeutral Company is the only one of the five schemes to charge VAT yet it is the cheapest. For a return flight to Sydney the company charges £30.45 whereas Pure - the only one of these schemes to meet Defra’s standards - charges £51.45. The CarbonNeutral Company’s founder, Sue Welland, claims they are able to charge less than others schemes because “we have been in the market for 10 years, we are the largest and there are efficiencies that are delivered through scale”.

Some offsetting schemes invest in projects that aim to absorb the equivalent amount of carbon emitted, whereas others tackle the problem at source by investing in renewable energy projects that avoid carbon emissions being produced.

Carbonbalanced.org is managed by the World Land Trust, which uses donations to fund reforestation projects in Ecuador whereas Climate Care invests in renewable energy programmes and energy-efficient projects in the Third World. Climate Care's Michael Buick says his company doesn’t support projects in the UK as it “would be helping the government achieve what it has to achieve anyway”, preferring instead to support projects that he says “would not have happened otherwise” in non-industrialised countries that haven’t signed up to the Kyoto Agreement, such as Honduras and Kazakstan. The CarbonNeutral Company supports both carbon sequestration projects and energy-efficient and renewable energy projects in the UK and abroad. It works with a KPMG-audited quality assurance standard – the "CarbonNeutral Protocol", which it says ensures that the offsetting projects it supports are properly monitored.

Travel companies that currently offset through the CarbonNeutral Company include car rental company Avis, Crystal Holidays and the recently launched transatlantic business class airline Silverjet. In November, Lastminute.com launched a "carbonwise" offsetting facility with Climate Care and recently reported that one in ten of its customer have used it, offsetting some 2,000 tonnes of carbon dioxide. According to Lastminute, London–Edinburgh is the “greenest” route, with 23 per cent of customers choosing to offset their journey between the two cities.

While none of the schemes claim that carbon offsetting is the solution to climate change, they do provide customers with a way of "doing something" about the carbon footprint of their journey. According to Michael Buick, offsetting is more than just providing for a guilt-free trip: “Offsetting is really just an early form of global carbon market. What we need to do is reduce the overall production of carbon as economically painless and efficiently as possible.”

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