CO₂ fertilisation has increased maximum foliage cover across the globe’s warm, arid environments

Abstract: Satellite observations reveal a greening of the globe over recent decades. The role in this greening of the ‘CO2 fertilization’ effect – the enhancement of photosynthesis due to rising CO2 levels – is yet to be established. The direct CO2 effect on vegetation should be most clearly expressed in warm, arid environments where water is the dominant limit to vegetation growth.

Using gas exchange theory, we predict that the 14% increase in atmospheric CO2 (1982–2010) led to a 5 to 10% increase in green foliage cover in warm, arid environments. Satellite observations, analysed to remove the effect of variations in rainfall, show that cover across these environments has increased by 11%.

Our results confirm that the anticipated CO2 fertilization effect is occurring alongside ongoing anthropogenic perturbations to the carbon cycle and that the fertilisation effect is now a significant land surface process. In the Journal Geophysical Letters 31 May 2013

Global Greening

Rising atmospheric carbon dioxide levels has triggered a “greening” of dry land grassy regions around the world due to a fertilization effect that has dramatically increased plant growth, reports a new study published in Geophysical Research Letters.

The study is based on analysis of satellite imagery in dry parts of North America, Australia’s outback, the Middle East, and Africa. Controlling for precipitation, air temperature, the amount of light, and land-use changes, Randall Donohue of Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) and colleagues found an astonishing eleven percent increase in foliage just 30 years (1982 and 2010). During this same time frame atmospheric CO2 levels increased 14 percent.

“Lots of papers have shown an average increase in vegetation across the globe, and there is a lot of speculation about what’s causing that,” said Donohue in a statement. “Up until this point, they’ve linked the greening to fairly obvious climatic variables, such as a rise in temperature where it is normally cold or a rise in rainfall where it is normally dry. Lots of those papers speculated about the CO2 effect, but it has been very difficult to prove.”

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The researchers say that the CO2 fertilization effect could favor a transition from grasslands to woodlands in forests in these regions, provided precipitation levels are sufficient to sustain trees. The greening effect already is resulting in declining dust that blows from arid lands. That dust is a critical resource for ocean plant life. Read more about this Yin and Yang relationship of dust and ocean plants.

The authors note that this is a dry grassland greening and that tropical forests are not showing increased greening because, unlike grasslands, their leaf cover is “already about as extensive as it can get”.

“Leaf cover in warm, wet places like tropical rainforests is already about as extensive as it can get and is unlikely to increase with higher CO­2 concentrations,” explained a statement from the American Geophysical Union, which publishes Geophysical Research Letters. “In warm, dry places, on the other hand, leaf cover is less complete, so plants there will make more leaves if they have enough water to do so.”

To read more on how the greening of the land results in the destruction of ocean pastures follow this link…..