Every year I take a chainsaw to at least five trees. Over the past couple of decades, I've felled a fair-sized forest. And these were no water-greedy pines or space-invader eucalypts either. These were precious: yellow-woods, stinkwoods, a couple of silver-trees too most likely.
It's a splendidly disastrous sound, when a stately lord of the plant kingdom bites the dust.
OK, no, I don't mean this literally of course; I've never committed first-degree arboreal murder. But I do drive a car, which means I've been pumping out roughly* five to six metric tonnes of carbon dioxide every year since I got my licence. A fully-grown tree, over the course of its life-time, sequesters, or absorbs, roughly* 1 tonne of atmospheric CO2.
Well, on the face of it. As with anything to do with natural systems – and this is a serious reason why people get weary and throw up their hands at environmental issues – it’s just not so simple.
Trees can’t save us. It is far, far more effective to keep the carbon tucked away unmolested in fossil fuels underground in the first place, than to release it, as we do, like an evil genie into the atmosphere. Unless someone finds, and quickly, a magic lamp and a way to stuff the genie back in, the only real hope we have of curbing climate change is radical emissions reduction. Planting trees is something, but not enough, not nearly. It is naïve, and dangerous, to think we can expunge our environmental sins this way.
Trees die. And when they do, whether by chainsaw, fire or disease, they release their stored carbon back into the atmosphere. Planting a tree to fight atmospheric carbon is only really meaningful if the tree endures long enough. To successfully store that carbon, you need your tree to reach maturity, and this is hard to guarantee.
Trees' net contribution to global cooling is pretty much impossible to quantify accurately. There are numerous throw-up-one's-hands-inducing controversies and complications with regards to this. For example, trees cool the planet down by absorbing CO2 and producing water vapour, but they may also have a warming effect because darker leaves tend to reflect sunlight less well than lighter surface areas. And reforestation itself might disturb and release carbon held in the soil.