Are carbon dioxide emissions from humans’ largely industrial society today “greening” Earth? The answer appears to be yes, as a new study finds that added greening, prompted by rising CO2 levels could cover twice the size of mainland United States.
While climate skeptics argued that these findings vouch for the benefits of added carbon emissions, the researchers were quick to clarify that the effects of so-called CO2 fertilization diminish over time, the negatives potentially outweighing the positives.
The team of 33 scientists from eight countries, using data from satellite sensors in the past 33 years, demonstrated significant greening of one-fourth to a half of the planet’s land, which represents increased plant and tree leaves. In turn, this could slow the pace of climate change as more plants draw CO2 from the air.
"The greening … is equivalent to adding a green continent about two-times the size of mainland USA (18 million square kilometers), and has the ability to fundamentally change the cycling of water and carbon in the climate system," said lead study author and Peking University researcher Zaichun Zhu.
The team, using computer modeling to mimic plant growth observed in the satellite data, showed that while their research did not connect greening with plants’ carbon storage, other studies had previously reported growing carbon sink on land since the 1980s – aligned with the idea of a “greening Earth.”
While climate skeptics – particularly those who argue against carbon emission cuts to mitigate climate change – could consider these results favorable, the team added that plants adjust to rising CO2 concentration and the fertilization effect eventually diminishes.
CO2 fertilization, too, is only one aspect – there are also key factors such as nitrogen fertilization, land management and climate change itself influencing Earth’s greening.
Lead author and Boston University professor Ranga Myneni told BBC News that the added tree growth won’t also be able to compensate for the rising sea levels, global warming, glacial melting and ocean acidification – to name a few events – that are plaguing the planet.
Co-author and Exeter University professor Pierre Friedlingstein explained that plants’ carbon uptake from considered in the Intergovernmental Panel on Climate Change (IPCC) models, but emerged as among the main sources of uncertainty in forthcoming climate forecasts.
Earth’s warming releases CO2, mainly though the rise in the decomposition of organic matter in soil, permafrost thawing, soil drying and decreased photosynthesis – all lead to grave consequences for tropical vegetation.
Carbon sinks, including forests could become sources if carbon loss from warming surfaces becomes bigger than carbon gain from fertilization, according to Friedlingstein. However, he adds that it is uncertain when this would happen.
“Hopefully, the world will follow the Paris agreement objectives and limit warming below 2C,” he said.
The burning of coal, gas and fossil fuels releases carbon dioxide into the atmosphere. CO2 levels in the air are steadily increasing since the industrial period, currently at a point not seen in at least 500,000 thousand years and implicated in climate change
The findings were published in the journal Nature Climate Change.
Photo: Loren Kerns | Flickr
