Also, "the greening effect may not apply to the world's driest regions. Beth Newingham of the University of Idaho, Moscow, recently published the result of a 10-year experiment involving a greenhouse set up in the Mojave desert of Nevada. She found "no sustained increase in biomass" when extra CO2 was pumped into the greenhouse. "You cannot assume that all these deserts respond the same," she says. "Enough water needs to be present for the plants to respond at all."
The extra plant growth could have knock-on effects on climate, Donohue says, by increasing rainfall, affecting river flows and changing the likelihood of wildfires. It will also absorb more CO2 from the air, potentially damping down global warming but also limiting the CO2 fertilisation effect itself.
Randall Donohue [CSIRO in Canberra] cannot yet say to what extent CO2 fertilisation will affect vegetation in the coming decades."