Green cover in India absorbed more carbon than it emitted annually: Study

The green cover in India has absorbed more carbon than it emitted annually in the last decade, but the rate of sequestration declines during extreme climate events such as drought, a study has revealed.

The study by researchers at the Indian Institute of Science Education and Research (IISER), Bhopal, also stressed the critical role of vegetation in climate change mitigation and adaptation.

Green vegetation absorbs carbon dioxide (CO2) from the atmosphere through photosynthesis and releases it back into the air through respiration.

"The overall balance between this uptake and release of CO2 is known as the net ecosystem exchange (NEE). When the NEE is positive, it means vegetation is releasing more carbon than it absorbs, and when it's negative, it indicates that the vegetation is effectively storing carbon," said Dhanyalekshmi Pillai, associate professor, head of the Max Planck Partner Group Germany, and of the Earth and Environmental Sciences, IISER Bhopal.

"For the last decade, India's (green) ecosystem absorbed more carbon than they emitted annually, with annual NEE estimates ranging from 380 to 530 million tonnes of carbon per year," she said.

Researcher and co-author of the paper, Aparnna Ravi, said this level of carbon sequestration is impressive but tends to decline in response to climate extremes, emphasising the critical role of vegetation in climate change mitigation and adaptation.

Scientists also studied how different types of vegetation across India help absorb CO2 each year.

Pillai said evergreen forests in India are highly efficient in capturing CO2 through photosynthesis. However, the deciduous forests in central India released more carbon into the atmosphere as plant respiration surpassed primary productivity.

"They (green vegetation) released 210 million tonnes of carbon annually, acting as carbon sources. Although croplands are less effective at absorbing carbon per unit area than forests, their extensive coverage across the country benefits significant CO2 removal from the atmosphere," she said.

Pillai said the sequestration rate is not constant but shows a decreasing trend, especially in response to drought.

She said drought is an example of climate extremes, and these conditions are increasing due to climate change.

"Green vegetation is favouring us (reducing global warming), but the sequestration potential cannot be limitless...under climate extremes, it shows decreasing sequestration. This is concerning," Pillai said.

She said the study reflects on creating and implementing effective climate policies and ecosystem management in consonance with nationally prioritised action plans.

IISER scientists, in collaboration with international experts, led and established an innovative technology-driven approach using highly resolved observations of plants' fluorescence ("glow") and advanced physics-based computer models to quantify vegetation's carbon sequestration potential across India for the first time.

In this novel approach, IISER-Bhopal researchers led long-term analyses across India by tracking several thousands of observational records of the last 10 years (2012-22), together with research experts from the Max Planck Institute for Biogeochemistry (Germany), University of Exeter (United Kingdom) and National Remote Sensing Centre (India).

Pillai said this newly demonstrated system also benefits from the recently available radiance observations from multiple satellite instruments, including the TROPOMI instrument onboard the Sentinel-2 satellite.

She said the method is more sensitive to detecting changes in ecosystem responses widely across the country than the commonly employed global methods that lack sufficient in-situ carbon measurements.

"By integrating interdisciplinary national and international expertise, IISER-B research focuses on uncovering the complex ecosystem processes that govern carbon sequestration and their resilience to climate extremes," Pillai said.