It was discovered last year through satellite data that the Earth’s global forest loss was actually reversing. Now an international team of scientists have quantified the change for the last 30 years to be equivalent to a green continent more than twice the size of Australia (18 million km²).
Published in the journal Nature Climate Change, the study titled “Greening of the Earth and its Drivers” brought together an international team of 32 authors from 24, including researchers from Australia’s CSIRO. The study used data from NASA’s MODIS and NOAA’s AVHRR satellite sensors of the past 33 years to quantify the greening, which represents an increase in leaves on plants and trees.
It is believed that the main cause of the greening has been the increase in carbon dioxide globally that is leading to higher rates of what is known as CO2 fertilisation. This is where plants use carbon dioxide as food to fuel their growth by turning it into sugar. When there is more carbon dioxide plants produce more sugar, and this has led to the increased vegetation. The researchers found that up to half the world’s land is becoming greener as a result. The study authors note that the greening has the ability to fundamentally change the cycling of water and carbon in the climate system.
“We were able to tie the greening largely to the fertilising effect of rising atmospheric CO2 concentration by tasking several computer models to mimic plant growth observed in the satellite data” says co-author Prof. Ranga Myneni of the Department of Earth and Environment at Boston University, USA.
About 85% of the Earth’s icefree lands are covered by vegetation. The area of all green leaves on Earth is equal to, on average, 32% of the Earth’s total surface area- oceans, lands and permanent ice sheets combined.
The study also highlights that CO2 fertilisation is only one, albeit a predominant, reason why the Earth is greening. The study also identified climate change, nitrogen fertilisation and land management as other important reasons.
Co-author Dr. Josep Canadell of the CSIRO Oceans and Atmosphere Division in Canberra, Australia and leader of the Global Carbon Project said that “while the detection of greening is based on measurements, the attribution to various drivers is based on models, and these models have known deficiencies. Future works will undoubtedly question and refine our results.”