James Randerson, science correspondent
Friday December 23, 2005
Brides and grooms do it. Transatlantic travellers do it. And you might even be getting it for Christmas. Neutralising your carbon emissions is becoming the must-do activity for the eco-conscious citizen. But now an international team of scientists has raised an unexpected objection: some tree-planting projects may, they suggest, be doing more harm than good.
Carbon offsetting allows people to pay someone else to atone for their climate sins by soaking up the CO2 that they produce. And with the consequences of global warming becoming more apparent, more Britons are opting to undo their personal share of the damage.
Last year companies and individuals in the UK spent around £4m offsetting carbon emissions. The Kyoto protocol allows member countries to do the same through carbon trading.
But it seems the guilt-free option is not as simple as writing a cheque and leaving it to someone else to sort out. Researchers have found that planting trees to soak up carbon can have detrimental knock on effects. "I believe we haven't thought through the consequences of this," says team-member Robert Jackson at Duke University in North Carolina, "I think the policy could backfire on us, but it will take decades to play out."
His team pooled more than 500 separate yearly observations from studies from five continents which compared planted areas with plots nearby that did not have trees. They report in Science that the plantations had a drastic effect on stream flow. By sucking water out of the ground and evaporating it from their leaves the trees reduced flow by half. And 13% of streams dried up for at least a year. This would have effects downstream where less water would be available for plants and animals.
The team found that nutrients in the soil were also affected by tree planting. Calcium, magnesium and potassium were all depleted while sodium was enriched, meaning that plantation soil was more salty on average. All of these changes would affect the range of plant species.
Dr Jackson says the two most common plantation species are pines and eucalyptus trees. These fast-growing species rapidly suck CO2 out of the atmosphere, but they result in monoculture forests which support a meagre range of biodiversity. Dr Jackson stresses that planting trees is not a bad thing per se, but schemes that are not well thought through can be environmentally harmful.
Tree-planting has always been a controversial method of soaking up CO2 because it is little more than a short term fix. Once the trees die they rot, releasing the carbon back into the atmosphere. "We are buying a few decades to transform our economies," says Dr Jackson.
Chris Field, an ecologist at the Carnegie Institution of Washington in Stanford, California, agrees. "It is not a slam dunk in terms of providing the kind of carbon benefit we would like to have," he says, "In the long run, solving the carbon problem is going to be more about reducing emissions rather than storage."
So where does this leave the eco-minded citizen who wants to tread a lighter carbon footprint? "Start by doing what you can yourself," says Tom Delay, chief executive of the Carbon Trust, a government funded company that is charged with helping UK businesses reduce their carbon emissions. "Most of the actions you can take will save you money as well as have a climate benefit." So installing energy saving light bulbs, insulating the loft or using the car less is a good start.
When it comes to buying a carbon offset, things get more tricky. "It's something of a wild west at the moment," says Bill Sneyd, operations direction of The Carbon Neutral Company (formerly known as Future Forests), the UK's largest company selling carbon offsets. This year it planted just under 300 hectares (750 acres) of new forest. Their plantations are planted with 90% native species, but he says the range of tree-planting options on offer vary widely in their knock-on effects on environment.
Tom Morton, director of Climate Care, a not-for-profit organisation based in Oxford, says tree planting is often the form of carbon offset that is most recognisable with the public. "These are often the easiest projects for people to understand." But he believes the biggest gains will come through new technologies. Four fifths of Climate Care's funding goes into supporting energy efficient or low-carbon technologies, for example training people in Madagascar to use energy efficient cooking stoves.
How to ease your climate conscience and neutralise your carbon emissions
· If you want to support forestry make sure the plantation will use native species/promote biodiversity
· Make sure it is protected from future logging or fire
· When donating to a company offering carbon offset projects check the cash is actually needed to get the project off the ground · Check the project has the support of local people · Ensure it represents a cost effective way of reducing carbon - has a responsible company or not-for-profit organisation audited the project?
· Consider supporting other carbon reduction options, such as funding energy efficient equipment or businesses selling low carbon technology