Talking Point: Carbon offsetting

Until recently, the flying business traveller needed only to worry about being fresh enough to work coherently when they touched down. Now they have guilt to cope with as well.

Simply by going about their business, most scientists believe travel is fuelling climate change. While the actual extent of aviation's contribution to global warming is hotly contested, there is no doubt that it is a new, key driver.

The consensus of most scientists and environmentalists is that aviation contributes four per cent of global carbon dioxide emissions. The figure sounds low, but may sound higher if you consider how few businesses would describe four per cent of anything, from profits to expenses, as a negligible issue. Furthermore, scientists argue that aviation's emissions are reinforced by the fact that contrails deposited at 30,000ft further magnify climate change (a process called radiative forcing). Friends of the Earth calculates that by 2050, aviation could contribute 15 per cent of all greenhouse gas emissions.

The most fashionable option for those seeking to assuage their guilt is to offset their carbon emissions. This can be done by paying a number of organisations to plant trees that can grow to absorb the equivalent carbon dioxide from your flight and convert it into harmless oxygen and wood; or invest in a project in a developing country that encourages the use of alternative or low-carbon fuels. They can also invest in biodiversity on your behalf.

Choosing the right offset company is crucial, and most are monitored independently to ensure that the emissions reductions you have paid for are being achieved. Costs vary. The cost of offsetting a flight from London to Nairobi ranges from £11 to £36 with most of the offset companies, such as Climate Care, Envirotrade and CO2Balance. The most expensive company for offsetting is usually Atmosfair, a German company, which in this case charges you £63, though the company says this is because it has the most rigorous approach to offsetting. Atmosfair has also been independently audited as only offering products that adhere to international standards for carbon offsets.

Hannah Lucas, of Bristol, who travels regularly to eastern Europe to conduct food safety tests for a British food processing company, agrees with the idea of offsetting trips, but feels it is only part of the solution. " If I can be certain that the companies involved really do plant the trees then I can buy into that – it seems a good way to offset the emissions from my flight," she said. "But companies also need to think hard about whether we all need to fly so much. I often seem to go away for two days, twice a week, when the trips could be combined into a slightly longer one, reducing my time away and reducing the related emissions."

And yet there is a nagging suspicion that the cost of offsetting – with the exception of Atmosfair – is low, perhaps even too good to be true. Even the most well-meaning of buyers now find that long plane trips can be offset for tremendously low costs. This had led to claims of a "greenwash". "Offsetting schemes are a cheap way to carry on polluting, when what we really need to be doing is reducing emission levels," said Helen Burley, co-author of a forthcoming Friends of the Earth book on Climate Change, Cool Life, Cool Planet. "If a tree is to store the carbon from your flight, it needs to still be around in 100 years time, which is hard to guarantee.

"Renewable energy schemes may do more good – but these only really count towards offsetting if it is clear that there is no way the project would have happened without your money. If you want to invest in sustainable energy projects, the best way to do it is to make a donation to a charity that is involved in clean energy projects in developing countries."

The message is clear enough. By all means pay someone to plant trees, but the best way to compensate for the extra carbon you're adding to the atmosphere is to cut your emissions back at work or at home.