The Greening Phenomenon Explained
For years, scientists have observed a global trend of 'greening'—an increase in the leaf area of vegetation. At the forefront of this are India and China. Satellite observations have confirmed that intensive agriculture and ambitious tree-planting programmes
are significant contributors. In India, a staggering 82% of this greening trend has been attributed to the intensive cultivation of food crops. This has been achieved not by expanding the land area for crops, which has remained relatively stable since the early 2000s, but through practices like multiple cropping, where fields are replanted to yield several harvests a year. This has boosted food production significantly. However, this agricultural greening is heavily reliant on another critical resource: water, particularly from groundwater irrigation.
Carbon Dioxide's Double-Edged Role
A key driver of this increased plant growth is the rising concentration of carbon dioxide (CO2) in the atmosphere. This is known as the 'CO2 fertilization effect'. In essence, with more CO2 available, plants can photosynthesise more efficiently, which stimulates their growth. Some studies suggest that this effect accounts for a large portion of the global greening trend. A recent study led by the Indian Institute of Tropical Meteorology (IITM) projects that this trend will continue, with India's vegetation productivity, or Gross Primary Production (GPP), potentially doubling by the year 2100 under a high-emission scenario. The strongest gains are forecast for the Indo-Gangetic Plain, Northeast India, and the Western Ghats.
Beyond CO2: The Human Factor
While the CO2 effect is a major factor, human intervention plays a decisive role. In India, the expansion of agriculture is the dominant force behind the greening signal detected by satellites. This contrasts with China, where large-scale afforestation programs contribute more significantly. The greening in India is therefore deeply tied to food production and the livelihoods of millions. However, this agricultural success story is propped up by extensive groundwater extraction. Regions like Punjab and Haryana have seen dramatic drops in groundwater tables due to tube-well irrigation for water-intensive crops. This makes the current greening trend potentially unsustainable if groundwater resources are depleted.
What the Future Models Predict
Advanced climate models, like the latest CMIP6, are providing a clearer, albeit complex, picture of India's future. These models forecast that the greening trend will not only continue but strengthen, driven by both CO2 fertilization and projected increases in rainfall. However, these same models highlight significant vulnerabilities. Hotter-than-normal years tend to suppress vegetation growth due to heat and moisture stress, an effect particularly strong in water-limited regions. Furthermore, some models predict that while overall vegetation might increase, up to 45% of India's forested areas could undergo a change in type, threatening biodiversity. Mountainous forests in the Himalayas are seen as particularly susceptible to these changes.
The Hidden Costs of Greening
The term 'greening' can be misleading if interpreted as a sign of overall ecosystem health. Increased vegetation, particularly from monoculture crops, does not necessarily offset the loss of natural biodiversity in other regions. Scientists caution that while plants may absorb more CO2, this doesn't automatically mean more carbon is stored long-term, as plants and soil also release carbon, especially under heat stress. Rising temperatures, even with more vegetation, can still harm ecosystems. The most critical trade-off is water. More plants, whether crops or new forests, can increase overall water demand, putting further stress on already scarce resources in a warming climate. Greening sustained by depleting aquifers is not a long-term solution.
