TREES CONTRIBUTE TO GLOBAL WARMING

Non-profit organization Greenfleet offers Australians a low-cost opportunity to make their cars carbon neutral:

For $40 (tax deductible), Greenfleet will plant 17 native trees on your behalf. These trees will help to create a forest, and as they grow will absorb the greenhouse gases that your car produces in one year (based on 4.3 tonnes of CO2 for the average car*).

Plenty of Australians have signed up:

Since 1997, Greenfleet has planted more than 2 million trees on behalf of Australian motorists and fleets. These forests will not be harvested and will create an investment in rural Australia for future generations.

The program is, however, not without problems:

Greenfleet, one of the nation's leading organisations helping individuals and companies offset carbon emissions, has for nearly three years been unable to find enough NSW land to plant the trees its subscribers have paid for.

In Queensland, a new property owner refused to recognise an agreement between his predecessor and Greenfleet. He bulldozed 20,000 trees, which then had to be replanted elsewhere.

Not only are they behind schedule, Greenfleet just plants the trees, it doesn't tend them or follow-up to see how they're doing. And despite Greenfleet's good intentions, planting trees to fight global warming is possibly a waste of time:

"What we have found is in the so-called mid-latitude region where the United States is located and majority of European countries are located, the climate benefits of planting will be nearly zero," said ecologist Govindasamy Bala of Lawrence Livermore National Laboratory.

"[In] the seasonally snow-covered regions [at even higher latitudes], planting new trees could be actually counter-productive," he told BBC News.

The team's modelling predicts that planting more trees in mid- and high-latitude locations could lead to a net warming of a few degrees by the year 2100.

So, we can do like Al Gore and buy some carbon credits to make us feel good about ourselves or, if we want to make a really meaningful contribution, we can buy chain saws and cut down some of those heat-trapping northern forests. The wood can be used to build rafts for polar bears.