Hot, dry and greening

Geophys. Res. Lett. http://doi.org/mqx (2013)

Increased atmospheric CO₂ concentrations can have a direct effect on plant growth in addition to indirect effects through changes in climate. Carbon dioxide is required for photosynthesis and the potential for a 'CO₂ fertilization' effect has long been recognized and studied in laboratory and field experiments. Satellite observations reveal a greening of the globe over recent decades — a pattern that would be expected if CO₂ is enhancing vegetation growth. However, disentangling the drivers of the greening trend is complicated, as there are many potential influences.

Randall Donohue from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia, and co-workers reduced the complexity of the attribution task by focusing on warm, dry environments where the CO₂ fertilization effect on plants should be most pronounced.

They predict — based on gas exchange theory — that recent increases in atmospheric CO₂ should have led to a 5–10% increase in green foliage. Satellite observations, with the effects of rainfall variations removed, indicate that vegetation cover has increased by 11%. These results confirm the anticipated CO₂ fertilization effect and show that it is a significant land surface process.