Thursday, December 22, 2005

Tree planting to get rid of your guilt a farce.

Swampy: As you read the reasons, can you pick one out that you couldn't reach by using common sense in general sort of way? I always thought the whole thing was ridiculous and nothing more than a useless self-esteem exercise to make people feel better about themselves.

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.
Yesterday we found out that Pollutants ward off global warming. The Guardian's science section must be having hissy fits writing this stuff up.

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