Unexpected increase in global vegetation and carbon capture

An international team of scientists, led by Australians, has used 20 years of satellite data to analyse the total amount of vegetation around the world - with surprising results.

Writing in the journal Nature Climate Change, the study authors stated, “Existing global estimates of aboveground biomass carbon (ABC) based on field survey data provide brief snapshots that are mainly limited to forest ecosystems.” The team therefore pioneered an entirely new technique to map changes in vegetation biomass over time, using satellite measurements of natural radio waves emitted from the Earth’s surface.

In spite of large-scale deforestation in the tropics, with the greatest declines occurring on the edge of the Amazon forests and in the Indonesian provinces of Sumatra and Kalimantan, the team found that vegetation has increased by almost the equivalent of 4 billion tonnes of carbon since 2003. Lead author Dr Yi Liu, from the University of New South Wales, said this increase has come from “a lucky combination of environmental and economic factors and massive tree-planting projects in China”.

“Vegetation increased on the savannahs in Australia, Africa and South America as a result of increasing rainfall, while in Russia and former Soviet republics we have seen the regrowth of forests on abandoned farmland,” Dr Liu explained. Co-author Professor Albert van Dijk, from the Australian National University, added that the increases in northern Australia were “unexpectedly large”, given the “ongoing land clearing, urbanisation and big droughts across other parts of Australia”.

Image credit: CSIRO Science Images.

The increased greening means the total amount of carbon captured in Australia’s vegetation has increased. However, co-author Dr Pep Canadell from CSIRO warned that the situation could rapidly reverse if the affected savannahs were to experience extended dry periods.

“This study shows this capture of carbon is very sensitive to year-to-year changes in rainfall over savannah regions, both for Australia and for the global CO₂ budget,” Dr Canadell said.

“It’s important to recognise that global warming would be happening faster if some of our CO₂ emissions were not captured by this vegetation growth.”

Dr Canadell warned that “about 50% of emissions from human activities stay in the atmosphere even after the other half is removed by terrestrial vegetation and oceans. The only way to stabilise the climate system is to reduce global fossil fuel emissions to zero.”

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