The planet is getting lusher.

However, Randall Donohue of Australia's national research istitute monitored vegetation at the edges of deserts in Australia, southern Africa, the US Southwest, North Africa, the Middle East and central Asia.

Carbon dioxide generated by human activity is stimulating photosynthesis and causing a beneficial greening of the Earth's surface.

However, factors such as higher temperatures, extra rainfall, and an increase in atmospherics CO2 -- which helps plants use water more efficiently -- could all be boosting vegetation, so pinning down the cause has been difficult.

However, it remains unclear whether the effect can counter any negative consequences of global warming, such as the spread of deserts.

Researchers claim to have shown that the increase in plant cover is due to this "CO2 fertilisation effect" rather than other causes.

He found that this figure rose by 11 per cent in these areas between 1982 and 2010, mirroring the rise in CO2.

If C02 levels were constant, then the amount of vegetation per unit of rainfall ought to be constant, too.

Donohue says this lends "strong support" to the idea that CO2 fertilisation drove the greening.

However, Donohue cannot yet say to what extent CO2 fertilisation will affect vegetation in the coming decades. But if it proves to be significant, the future may be much greener.

Climate change studies have predicted that many dry areas will get drier and that some deserts will expand, Donohue's findings make this less certain.