Leaf-level warming

Geophys. Res. Lett. 36, L02703 (2009)

Credit: JULES MONTGOMERY/VIACREATIVA

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.