Recent satellite studies have shown an overall increase in vegetation across the planet. Dramatic evidence of this can be seen in a recent analysis of NASA’s satellite data collected since 1982. This reveals a vigorous increase in vegetation growth between the 45th parallel north (the mid point between the North Pole and the equator) and the Arctic Ocean over the past 30 years.
Pinning down the cause of the increase has been difficult. A variety of factors related to climate change such as higher temperatures, extra rainfall, and an increase in atmospheric CO2, which helps plants use water more efficiently, could all be boosting vegetation. However, new research suggests that it is the increased levels of CO2 effect on photosynthesis that is responsible for making our planet increasingly lush.
The research suggests that the key factor in the greening of the planet is due to the increasing levels of carbon dioxide generated by human activity. Higher levels of CO2 stimulate photosynthesis and therefore cause a beneficial greening of the Earth’s surface. Scientists now claim green foliage cover across warm, arid environments has increased by up to 11% while there has been a 14% increase in CO2 over the past 28 years.
To home in on the effect of CO2, Randall Donohue of Australia’s national research institute, the CSIRO in Canberra, selected regions where there is ample warmth and sunlight, but only just enough rainfall for vegetation to grow, so any change in plant cover must be the result of a change in rainfall patterns or CO2 levels, or both. He monitored vegetation at the edges of deserts in Australia, southern Africa, the US Southwest, North Africa, the Middle East and central Asia.
If CO2 levels were constant, then the amount of vegetation per unit of rainfall ought to be constant, too. However, the team found that this figure rose by 11 per cent in these areas between 1982 and 2010, mirroring the rise in CO2 (Geophysical Research Letters, doi.org/mqx). Donohue says this lends “strong support” to the idea that CO2 fertilisation drove the greening.
Climate change studies have long predicted that many dry areas will get drier and that some deserts will expand. Donohue’s findings make this less certain. However, the greening effect may not apply to the world’s driest regions. Beth Newingham of the University of Idaho, states that “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 positive 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.
It remains unclear whether the “CO2 fertilisation effect” will be able to counter the negative consequences of global warming, such as the spread of deserts. Donohue cannot yet predict 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 and more benevolent than many climate modellers predict.
Sources include : The New Scientist, CSIRO
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