Pune: A new IITM-led study suggested that India could become progressively greener over the coming decades — forests, croplands and other vegetation are expected to grow more and absorb more carbon dioxide from the atmosphere.The study, published in the International Journal of Climatology, looked at past trends from 1985 to 2014 and projected changes up to 2100 using the latest climate models, called CMIP6 (Coupled Model Intercomparison Project Phase 6), under a high-emission scenario. Countries continue to burn large quantities of fossil fuels with little effort to cut emissions under this scenario, leading to much higher greenhouse gas levels by the end of the century.It found that GPP (Gross Primary Production) — a measure of how much carbon dioxide plants absorb through photosynthesis — rose across India from 729.1 grams of carbon per square metre per year or gC/m²/year in 1985 to 830.1 gC/m²/year in 2014. It is projected to nearly double to 1304.8 gC/m²/year by 2100.The study was led by Smrati Gupta and Yogesh K Tiwari of the Indian Institute of Tropical Meteorology (IITM), Pune, with Ravi K Kunchala of IIT Delhi, Ankur Srivastava of the University of Technology, Sydney, and Akhilesh S Raghubanshi of Banaras Hindu University. They said future GPP increases projected by CMIP6 were up to 2.5 times stronger than the historical trend, and significantly higher than earlier estimates from the older CMIP5 models.“The strongest gains, the study found, are likely across the Indo-Gangetic Plain, Northeast India and the Western Ghats — regions that already have dense forest cover and intensive agriculture. Arid Northwest India, by contrast, is projected to see little change. The long-term greening trend is mainly driven by the combined effect of rising atmospheric carbon dioxide, which stimulates plant growth through what is called CO₂ fertilisation, together with an increase in rainfall projected under the models,” said Tiwari.The researchers found that the enhanced GPP was linked more to stronger rainfall trends in the newer models rather than to any fundamental change in how sensitive vegetation was to climate.At the same time, the study distinguished this long-term trend from year-to-year variability. Using statistical techniques to separate persistent trends from short-term fluctuations, the authors found that hotter-than-normal years tend to suppress vegetation growth through heat and moisture stress, while wetter-than-normal years boost it — an effect that was strongest in semi-arid and water-limited regions such as Rajasthan, Gujarat and the Eastern Plateau.“We also cross-checked the modelled increase in GPP against real-world data on India’s changing land cover. Forest cover across the country rose from 20.6% to 21.6% of India’s geographical area between 1985 and 2014, according to Forest Survey of India data, while cropland area also expanded — a pattern the study found was broadly consistent with, and moderately correlated to, the simulated rise in GPP,” said Gupta.Tiwari cautioned that this did not mean climate change was good for India’s ecosystems. More plant growth, he said, did not automatically mean more carbon gets stored long-term, since plants and soil also release carbon back into the air, especially under heat stress — something earlier studies also found. Rising temperatures, he added, could still harm ecosystems and biodiversity even as vegetation grew more.The researchers said the findings could help improve estimates of India’s future carbon absorption and support climate adaptation planning. They called for further studies using ground-based data to make the projections more accurate.
