Geophys. Res. Lett. 36, L02703 (2009)
By losing less water, plants could worsen warming in a high-CO2 world, finds a new study. Stomata — the tiny pores on leaf surfaces that permit the exchange of water and gases with the atmosphere — close under elevated CO2 concentrations, returning less water to the atmosphere through the process known as transpiration.
Marie Doutriaux-Boucher of the Met Office Hadley Centre, UK, and colleagues used a coupled carbon–climate cycle model to examine the effect of suddenly doubling or quadrupling atmospheric CO2 concentrations on plant-induced changes in climate over a five-year period. To distinguish plant-mediated from non-plant-mediated effects on climate, they ran model simulations in which plants were exposed to or shielded from increased carbon dioxide. When plants were exposed to elevated CO2, global surface warming was increased by 13 and 16 per cent in the doubling and quadrupling experiments, respectively.
The increase in surface warming results from a rapid reduction in low-level cloud cover over mid-high latitude forests and the Amazon, according to the model results. The decline in cloud cover is probably due to a decline in water loss by plants under high-CO2 conditions, say the researchers.