Rising carbon dioxide greening the Earth
A study published in Nature Climate Change show the Earth has been getting greener over the past 30 years. While the researchers found between 25 to 50 per cent of all vegetated areas of the land have become greener, only 4 per cent have become browner.These included Mongolia, Argentina and areas of North America close to Alaska.Research shows this change has been driven by human activities, particularly the rising concentration of carbon dioxide in the atmosphere. This is perhaps the strongest evidence yet of how people have become a major force in the Earth’s functioning in a new age, we can call Anthropocene.The most comprehensive modelling of remote sensing data so far shows the area on Earth covered by plants in this time has increased by 18 million square kilometres.”The greening has the ability to fundamentally change the cycling of water and carbon in the climate system,” said Dr Zaichun Zhu, from Peking University in China and lead author of the new study.”This is a snapshot of humans’ global influence on the functioning of the entire global biosphere,” said co-author CSIRO’s Dr Pep Canadell of the Global Carbon Project.The new findings come from analysis of data from the past 33 years taken by three different satellite missions that measured the green light reflected by photosynthesising leaves.Dr Canadell said the remote sensing data was run through 10 global environmental change models to identify the cause of the greening.
About 85 per cent of Earth’s ice-free land is covered by plants, and each year photosynthesis soaks up about one quarter of the nearly 10 billion tonnes of carbon emitted by humans.Drs Zhu, Canadell and colleagues found that the 46 parts per million increase in atmospheric CO2 between 1982 and 2009 was responsible for 50 to 70 per cent of the observed greening.”Carbon fertilisation is the dominant process for greening across the globe, particularly in the tropics because there’s so much leaf area there,” Dr Canadell said.”The growth of CO2 in the atmosphere is almost exclusively due to fossil fuel burning and deforestation,” said Dr Canadell.The new study found other causes of the greening, including nitrogen from agricultural fertilisers.Dr Canadell said the greening has surprised scientists who expected to see more browning, given the increase in droughts associated with global warming.While south-eastern Australia also showed browning, overall the Australian continent was greening, said Dr Canadell.While a greener Earth might seem like a positive from CO2-induced global warming, along with milder winters and longer growing seasons, he said there were many more negative impacts including rising sea levels and severe weather.”These will eventually outweigh by far any benefit from the greening,” he said.