Opinion India’s carbon sink is weakening — climate policy can no longer ignore it
New research shows forests, wetlands and blue-carbon ecosystems are absorbing far less CO₂ under heat stress, threatening India’s net-zero pathway
Recent research by IIT Kharagpur supports this concern. It finds that forests’ photosynthetic efficiency — the physiological ability of plants to convert sunlight and CO₂ into biomass — has declined in key regions. 
By Suvajit Banerjee
When policymakers tally national climate progress, they often balance a country’s emissions with the carbon captured by forests, wetlands, and coasts — nature’s “negative emissions”. The logic appears straightforward: Plant more trees, lock away more carbon, and buy time for the clean-energy transition. But this ledger is now showing red flags. New scientific evidence reveals a critical divergence. A global multi-method study published in Nature Ecology & Evolution finds that terrestrial carbon sequestration weakens markedly during intense warm extremes because plants’ photosynthesis declines faster than respiration. The mechanics may sound technical, but the implication is simple: Heat waves, prolonged high vapour-pressure deficits and drying soils reduce the carbon plants can fix, sometimes abruptly.
This vulnerability was foreshadowed in 2023, when fast-turnaround carbon-budget analyses showed that land and ocean sinks absorbed far less CO₂ than expected — a temporary collapse of the natural buffer that had stabilised atmospheric CO₂ growth for decades. This discovery altered the arithmetic of every climate plan. What previously looked like a margin for slower decarbonisation suddenly narrowed.
India’s story adds another layer. The Global Forest Resources Assessment 2025 (GFRA, 2025) by the FAO ranks India fifth among global carbon sinks, noting that between 2021 and 2025, India’s forests and tree cover absorbed about 150 million tonnes (Mt) of CO₂ per year. These figures reflect successful afforestation programmes and sustained attention to tree cover. But while satellites show India is greening, whether the functional capacity of this expanded cover to absorb carbon is sustainable remains uncertain. We may be adding trees on the map while losing efficiency under the canopy. For a country targeting Net Zero by 2070, this is not a footnote. Treating natural sinks as a stable backstop risks mispricing mitigation, misallocating scarce funds, and under-protecting livelihoods dependent on resilient ecosystems.
Recent research by IIT Kharagpur supports this concern. It finds that forests’ photosynthetic efficiency — the physiological ability of plants to convert sunlight and CO₂ into biomass — has declined in key regions. Heat, drought stress, shifting precipitation patterns and forest fragmentation mean that a hectare of forest today often sequesters less carbon than it did two decades ago. National carbon accounting is measuring area, not output, and risks conflating the two.
Another overlooked asset is wetlands and coastal “blue carbon”. Recent fieldwork in Assam and studies from India’s mangrove belts and seagrass meadows document large, concentrated soil carbon stocks. Some wetlands store tens of thousands of kilograms of carbon per hectare in their soils. Yet, these ecosystems are routinely excluded from mainstream climate accounting, under-monitored and under-financed. Institutional gaps further limit India’s ability to translate this potential into reliable mitigation credits.
Policy blind-spots and net-zero risks
What this means for policy, economics and modelling is both complex and critical.
First, India’s NDCs and domestic targets cannot assume stable sink performance. Ecological and macroeconomic models that treat nature-based removal as a fixed parameter will overstate mitigation capacity and understate the cost of emissions reduction. If a 10–20 per cent decline in sink efficiency occurs regionally — a realistic scenario under heat and drought stress — national emission pathways and carbon-pricing designs shift significantly. Policymakers must stress-test plans against ‘sink weakening’ and consider reversibility risks such as fire, pests and drought. For Computable General Equilibrium (CGE) modellers and Ecologically-Extended Input-Output practitioners, incorporating this stress-test is now an essential modelling task.
Second, the right policy mix is not “more planting” alone. India needs a three-part ARM framework:
• Avoid: Protect and manage existing high-integrity forests.
• Restore: Repair degraded ecosystems with resilience-building interventions.
• Measure: Build rigorous monitoring and reporting systems to track actual carbon uptake.
India should also operationalise instruments like payments for ecosystem services and ensure climate-proofed restoration funding reflects the risk of reversal rather than rewarding one-off plantation counts.
Third, India must elevate wetlands and blue carbon in national climate policy. Carbon stored in mangroves, seagrasses and wetland soils is real and often durable, yet markets and policy rarely reflect their value. Strengthening institutional capacity for inventory, community stewardship and verified blue-carbon projects would be a high-value, low-regret investment for coastal and riparian communities.
Fourth, as natural sinks show signs of weakening, India should diversify its mitigation portfolio. Feasible technological removals — such as direct air capture pilots and enhanced weathering R&D— should be accelerated, while nature-based solutions remain central for co-benefits including biodiversity, water regulation and livelihoods. Economics must guide the mix: compare marginal abatement costs under varied risk scenarios and factor in social value, not simply the tonnage of carbon removed.
Finally, India’s economic policy must treat forests and coasts as living infrastructure requiring recurrent budgets. Trees are not a one-time capital expense; they need corridors, fire management, water security and community incentives. This means shifting some climate finance from headline plantation targets towards long-term maintenance, monitoring and adaptive management.
A changing global context
This concern is especially relevant in the aftermath of the COP deliberations in Brazil, where countries updated their net-zero pathways. While negotiations rightly emphasise emissions cuts and climate finance, they still largely treat natural sinks as stable assets. The science shows this assumption requires urgent re-examination if global mitigation plans are to remain credible. For India’s climate-policy community and economists who build models to inform decision-makers, key steps include embedding sink-degradation risk into scenario design, expanding land-use modules to account for non-linear sink behaviour, and conducting sensitivity analyses to determine how much additional mitigation or investment is necessary if nature’s removal capacity declines.
Way forward
The story here is not doom but clarity. Nature has bought us time, but it was never an unlimited credit line. India has comparative advantages — large land areas, strong community institutions, expanding blue-carbon opportunities. If economic planners and modellers treat nature as potent but fragile, India can craft resilient pathways that reduce emissions without over-betting on a single, unstable form of removal. The alternative is to discover too late that the balance sheet does not add up — and by then, the costs will be far higher.
The writer is fellow, CGE Modelling and Policy Analysis, NCAER, New Delhi
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