The amount of vegetation in the world, and the way it is spread across the planet, has changed significantly in the last three decades, researchers say.
They attribute more than half the changes they detected to the effects of the warming climate, with people responsible for only around a third. Surprisingly, perhaps, they are at a loss to attribute about 10 percent of the changes unequivocally to either the climate or us.
They say their work marks a scientific advance, because it has only recently become possible to quantify how far climate variability, human activity or a combination of the two are responsible for what is happening.
In a striking and perhaps unexpected development, the team found that while vegetation has declined south of the Equator, it has increased in the northern hemisphere.
The climate is what governs the seasonal activity of vegetation. In the humid mid-latitudes, temperature is the largest factor influencing plant growth.
In mainly dry areas, though, it is the availability of water and in high latitudes the amount of solar radiation that is key. And everywhere humans influence vegetation in myriad ways — and are influenced by it.
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