Climate change, this global warming thing, it's going to mean that the tropical forests frazzle up and then we all die, right? It will mena the death of the "lungs of the planet" – such as the miles upon miles of Amazon jungle – which turn CO2 into the O2 that we inhale. It's titsup for humanity, basically. Except, according to one new paper in Nature, that's not the way it will work. CO2 is indeed plant food and more plant food means more plants, more forests and thus we're all saved: or perhaps not quite as screwed as some seem to think at least.
The point is this:
Experimental studies have generally shown that plants do not show a large response to CO2 fertilisation. “However, most of these studies were conducted in northern ecosystems or on commercially important species” explains Steven Higgins, lead author of the study from the Biodiodversity and Climate Reseach Centre and Goethe-University. “In fact, only one experimental study has investigated how savanna plants will respond to changing CO2 concentrations and this study showed that savanna trees were essentially CO2-starved under pre-industrial CO2 concentrations, and that their growth really starts taking off at the CO2 concentrations we are currently experiencing.“
Purists will cavil at this description, but grasslands and forests compete with each other. Forest cover kills off the grass and thus grasslands only thrive where trees don't. Savannas are, to a useful level of truth, the front line where the battle is taking place. As the paper points out, the trees on these savannas are finding their growth limited by the amount of food they can get: the CO2 from the atmosphere. As we burn more fossils that will go up, the trees will get more food and forests will advance across those grasslands.
These burgeoning forests will then rather neatly lock up in the biosphere all that extra carbon that we have been releasing into the atmosphere. Or some of it. But the major point of this paper is that far from climate change being a threat to the tropical forests, it looks as if it will be the cause of more of them growing. Good news for those of us who like our unsustainable tropical hardwood furniture: it looks like there's going to be a lot more of it to go around soon enough.
Now all we have to hope for is that the upcoming IPCC report, the fifth, will report honestly and openly upon all the effects of rising CO2 levels so we can work out whether it's worth ditching industrial civilisation or not. Yes, I live in hope too. For this is actually the most important question in the entire subject. We know very well what the direct effect of a doubling of atmospheric CO2 is: a 0.7 degree rise in temperature – that's just straight physics. The idea that we might get 2 or 4 or 5 degrees of temperature change comes from the interaction of positive and negative feedback mechanisms. And we don't know what all of those mechanisms are, don't know the direction of some of them and are really very unsure indeed what the total value is. Which is a pity because it's really the only thing we're interested in. ®
Atmospheric CO2 forces abrupt vegetation shifts locally, but not globally by Steven Higgin and Simon Scheiter was published in Nature on 27 June.