Jane Powerson carbon dioxide
How big is a tonne of carbon dioxide? I mean, how much room does it take up? I'm wondering about this, because I recently emitted close to a tonne of the stuff in one fell swoop. Well, two swoops, actually, as the event in question was a round trip of ... 4,500-plus kilometres by air (you'll find my destination, if you're curious, in the gardening department of this magazine).
A tonne of CO2, I've discovered, is about the size of a three-bedroom house. Or, to be exact, at 25 degrees and one atmosphere of pressure, it's 556.2 cubic metres.
The curious thing about fossil fuels and CO2 (at least, to those of us who are not of a scientific bent) is that when you burn a tonne of the former you get two to four tonnes of the latter. The secret to this loaves-and-fishes situation is that when hydrocarbons (that is, fossil fuels) are set alight, each carbon atom bonds to two atoms of oxygen (making carbon dioxide), and the hydrogen goes off and liaises with more oxygen, creating H2O, or water. So, depending on what fuel you're burning, you're going to get more or less CO2, but you'll always get a great deal more than the weight of the original fuel.
Carbon offsets have become a popular way of supposedly mopping up the excess CO2 that our activities generate. Numerous companies will plant trees, distribute low-energy light bulbs to the developing world, invest in wind energy or otherwise cut down or soak up CO2 production somewhere else on the planet, and thus, in theory, cancel out the emissions created by the person paying for the offsets.
That's the theory. The reality is somewhat different, with the true value of many offset schemes being questionable or difficult to ascertain. For instance, TerraPass, the company that was chosen to make this year's Oscars "carbon neutral" (providing 45 tonnes of offsets - and a glass sculpture by the Irishman Simon Pearce - for each celebrity performer and presenter), proved not to be fulfilling the important criterion of "additionality". The largest scheme it funded (capturing methane from landfill in Arkansas) was happening anyway, so no additional emissions were being scrubbed away.
Because the carbon-offset industry is not satisfactorily monitored and regulated, it must be approached with some wariness. Friends of the Earth is just one of several environmental organisations that do not recommend buying offsets.
But, for those who have released a supernumerary cloud of CO2 (through flying, for example), and who want to pay, is there another solution? One strategy is to make a donation to a non-profit environmental organisation or to a charity that works in regions affected by climate change (pick anywhere in the developing world). This, of course, won't stop one from being labelled a "chequebook environmentalist", but at least there is more transparency about the money's destination. Another idea is, simply, to limit one's future flights. If you are so minded, and want to make a formal pledge, log on to www.flightpledge.org.uk.