The world is literally a greener place than it was 20 years ago, and data from NASA satellites has revealed a counterintuitive source for much of this new foliage: China and India, a NASA study reported.
The ambitious multiple tree-planting programs in China and intensive agriculture are the reasons behind the world’s biggest populations leading the increase in greening across the globe.
“China and India account for one-third of the greening, but contain only 9% of the planet’s land area covered in vegetation – a surprising finding, considering the general notion of land degradation in populous countries from overexploitation,” said Chi Chen of the Department of Earth and Environment at Boston University, Massachusetts.
'Greening' and 'browning' are the statistically significant increases and decreases, respectively, in the annual average green leaf area at a location over several years.The study said that changes in the average leaf size, number of leaves per plant, the density of plants, the species composition, duration of green-leaf presence owing to changes in the growing season and multiple cropping could also affect the results of greening and browning.
First detected using satellite data by Ranga Myneni of Boston University and colleagues in the mid-1990s, it was still unknown if the chief direct cause of the greening phenomenon was human activity.
The factors affecting the increase in leaf area include direct land-use management, climate change and CO2 fertilisation. Nitrogen deposition and recovery from natural disturbances are also indirectly responsible, according to the satellite data.
The yearly average of leaf area found in a fixed vegetated area represents the annual average Leaf Area Index (LAI) of the Earth. At present, the LAI of the Earth is 1.57.
The study said that food production in China and India had increased by over 35% since 2000, which is due to the increase in the harvested area through multiple cropping facilitated by fertiliser use and surface and groundwater irrigation.
The change in the greening trend may depend on numerous factors, both on a global scale and a local human level. In one instance, increased food production in India is facilitated by groundwater irrigation. If in the future, the groundwater is depleted, this trend might change, the report said.
“But, now that we know direct human influence is a key driver of the greening Earth, we need to factor this into our climate models,” said Rama Nemani, a research scientist at NASA’s Ames Research Center, in California’s Silicon Valley, and co-author of the satellite data work. “This will help scientists make better predictions about the behaviour of different Earth systems, which will help countries make better decisions about how and when to take action.”