There are competing theories regarding what impact higher concentrations of carbon dioxide in the atmosphere would have on plant life in semi-arid regions of the world. One suggests that with more CO2 available, plants would be more efficiently capable of absorbing all the greenhouse gas required for photosynthesis, thereby sacrificing less water. This would require less water from the local environment, with a net result of fuller rivers and streams in water-stressed locations.
Unfortunately, a recent study has shown the opposite may be true. While individual plants may indeed use less water, the overall impact of extra carbon dioxide is more plants, resulting in a much higher demand for water resources among the competing vegetation. ‘It’s good for the plants that higher CO2 concentrations mean greenness is increasing, but they use more water, meaning there’s less for rivers, and less for us,’ says study author Colin Prentice, AXA Chair in Biosphere and Climate Impacts from the Department of Life Sciences at Imperial College, London.
The impact can be seen from space, with satellite images showing a visible greening of Australia between 1982 and 2010, the period for which climate and flow records were analysed. ‘It’s amazing that the results translate from experiments on individual plants to this kind of scale,’ continues Prentice. ‘But it’s reassuring, too, because this is what our theoretical models predict and we can show that the numbers stack up.’
This article was published in the December 2015 edition of Geographical magazine.