A new study reports China’s planting of trees and India’s intensive crop cultivation as the main reasons why the Earth is greening throwing doubt on the role of carbon dioxide fertilization, which climate change skeptics have touted as the beneficial effects of otherwise benign increase of carbon dioxide in the atmosphere from burning of fossil fuels and tropical deforestation.
A team of researchers led by Boston University has just published a study titled “China and India lead in greening of the World through land-use management” in the journal Nature Sustainability showing that there is now about five and half million square kilometers of extra green leaf area yearly compared to the early 2000s, a 5% increase, but that this is mostly due to intensive land-use in the two most populous countries, China and India. This contradicts a widely-reported previous study, by some of the same researchers, that found carbon dioxide (CO2) fertilization as the main reason for the greening of Earth’s lands – a finding which climate change skeptics have claimed as benefits of CO2 pollution of the atmosphere. The current study uses high quality satellite data from NASA’s MODIS sensors that view the entire Earth twice a day at 500 m resolution to base their findings and identifies poor representation of how humans use the land in Earth System Models as the reason for the previous conclusion.
The greening over the last two decades represents an increase in leaf area on plants and trees equivalent to the areal span of the entire Amazonian rainforests. Green leaves produce sugars using energy in the sunlight to mix CO2 drawn in from the air with water and nutrients pumped in from the ground. These sugars are the source of food, fiber and fuel for life on Earth. “China and India account for one-third of the greening but contain only 9% of the global vegetated land area, a finding that hints at human land-use, rather than global scale phenomena such as CO2 fertilization or climate change, as the dominant driver of Earth’s greening” said lead author Chi Chen of the Department of Earth and Environment at Boston University, USA.
The greening is due to intensive agriculture in China and India to feed their large populations and ambitious tree planting in China – the so-called Green Great Wall – with the goal of mitigating soil erosion, air pollution and climate change. “These programs have been quite successful in ameliorating land degradation, lowering surface temperatures and enhancing carbon storage” said co-author Prof. Shilong Piao of the College of Urban of Environmental Sciences at Peking University, PRC.
Land area under crops in China and India is comparable, about 2 million square kilometers, and has not changed much since the early 2000s. However, total food production (grains, vegetables, fruits, etc.) has increased greatly – by about 35-40% since 2000. “Increased food production in China and India is due to increased harvest area accomplished through multiple cropping in a year and facilitated by heavy fertilizer use and surface/ground-water irrigation” said co-author Dr. Rama Nemani of NASA’s Ames Research Center, USA.
Every year, about one-half of the 10-11 billion tons of carbon emitted in to the atmosphere from burning of fossil fuels and tropical deforestation remains temporarily stored, in about equal parts, in the oceans and plants – the so-called carbon sinks. “Unlike greening due to large-scale tree plantations in China, sustainable forestry practices in Western Europe and re-wilding of abandoned lands in Eastern Europe, greening due to intensive agriculture does not proportionately reduce atmospheric CO2 concentration by enhancing the land carbon sink” said co-author Dr. Victor Brovkin of Max Planck Institute for Meteorology, Germany. He added that although browning is seen only in 5% of the global vegetated area, this is for the most part centered in the tropical natural forests of Brazil, Congo and Indonesia, and this raises questions about those ecosystems’ sustainability and biodiversity.
“The current study clearly points to human use of land as one dominant driver of Earth’s greening but it is unable to quantify the precise role of other drivers, namely CO2 fertilization, climate change, nitrogen deposition, recovery from disturbances, etc.” said co-author Dr. Philippe Ciais of the Laboratory of Climate and Environmental Sciences, Gif-sur-Yvette, France. He added that Earth System Models should be refined to include a realistic representation of key land-use practices identified in this study – multiple cropping, irrigation and fertilizer use, fallowing and abandonment of land, afforestation, reforestation and deforestation.
“Alerted by a 1996 report in the journal Nature by the late Charles David Keeling of the Scripps Institution for Oceanography, Ranga Myneni of Boston University and colleagues detected the greening phenomenon using satellite data, first in the far northerly lands and subsequently at the global scale” said co-author Dr. Hans Tømmervik of the Norwegian Institute for Nature Research. He added that recent works of co-authors Prof. Rasmus Fensholt of the University of Copenhagen, Denmark, and Dr. Richard Fuchs of the Karlsruhe Institute of Technology, Germany, provide strong additional evidence for the connection between human land-use and the greening phenomenon in Sub-Saharan Africa and Europe.
Read the paper at Nature Sustainability
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