Tropical Forests as a Global Carbon Sink

A carbon sink is anything that takes in more carbon dioxide from the air than it gives out. Tropical forests, the dense forests near the equator, are among the world's most important natural carbon sinks. Their trees pull carbon dioxide out of the air and store the carbon in wood, roots and soil. By doing this, they slow down global warming.

How does a forest absorb carbon?

Trees take in carbon dioxide during photosynthesis and use sunlight to turn it into sugar and wood. But trees also release carbon dioxide when they breathe (respiration), and when they die and rot or burn. A forest is a sink when growth takes in more carbon than respiration, decay and fire release. It becomes a source when it releases more than it absorbs. Think of it like a bank account: growth is the deposit, and death, decay and fire are withdrawals.

Where are the tropical forests?

There are three great blocks:

• The Amazon in South America, the largest, spread over Brazil, Peru, Colombia and other countries.
• The Congo Basin in Central Africa, the second largest.
• Southeast Asia and New Guinea, including Indonesia, Malaysia and Papua New Guinea.

Tropical forests make up about 45% of the world's forest area. They also hold most of the Earth's land plant species.

Why do they matter so much?

• Carbon storage: They store huge amounts of carbon in trees and soil. Losing them releases it back into the air.
• Carbon uptake: Intact tropical forests absorb a large share of human carbon dioxide emissions every year.
• Rain making: In the Amazon, trees release water vapour that falls again as rain further inland. This "moisture recycling" keeps the forest wet and also feeds rain to farms far away.
• Biodiversity and people: Millions of people, including indigenous communities, depend on these forests for food, water and income.

Is the sink getting weaker?

Several major studies say yes:

• Hubau and others (2020, Nature) studied decades of tree measurements in Africa and the Amazon. They found that intact tropical forests' carbon uptake peaked in the 1990s. These forests removed about 17% of human-made carbon dioxide emissions in the 1990s, but only about 6% in the 2010s. The Amazon sink was weakening fast, while the African sink stayed steadier for longer.
• Gatti and others (2021, Nature) used air samples from aircraft over the Amazon (2010-2018). They found that the south-eastern Amazon had become a net carbon source, because of deforestation, fire and local warming and drying.

Why is the sink weakening?

• Heat and drought: Hotter, drier years kill more trees and slow growth. Strong El Niño years cause sharp drops in uptake.
• Deforestation and fire: Clearing land for cattle, soy, palm oil and mining releases carbon directly and dries out the remaining forest.
• Degradation: Logging, edges and small fires thin out the forest even when it is not fully cleared.
• Less resilience: Forests that have suffered repeated droughts recover more slowly from the next one.

What is a tipping point?

Scientists warn that the Amazon could cross a threshold beyond which large parts turn into dry, savanna-like land. In a 2018 editorial, scientists Thomas Lovejoy and Carlos Nobre estimated this tipping point at about 20-25% deforestation of the Amazon, combined with climate change and fire. Once crossed, the change may be hard or impossible to reverse, because less forest means less rain, and less rain means even less forest.

India's position

Most of India's forests are tropical: tropical dry deciduous and tropical moist deciduous forests cover the largest area, with tropical evergreen forests in the Western Ghats, the Northeast and the Andaman and Nicobar Islands. According to the India State of Forest Report (ISFR) 2023, published by the Forest Survey of India:

• Forest cover is 7,15,343 sq km (21.76% of India's area); forest and tree cover together is 25.17%.
• Total forest carbon stock is about 7,285.5 million tonnes, up 81.5 million tonnes since 2021.
• India has created about 2.29 billion tonnes of CO2-equivalent additional carbon sink compared with 2005, against its NDC (Nationally Determined Contribution) target of 2.5 to 3 billion tonnes additional sink by 2030 through more forest and tree cover.

Global efforts to protect forests

• REDD+ (Reducing Emissions from Deforestation and Forest Degradation, plus conservation and sustainable management) pays developing countries for keeping forests standing. Its rulebook, the Warsaw Framework for REDD+, was agreed at COP19 in 2013, and Article 5 of the Paris Agreement (2015) supports it.
• Glasgow Leaders' Declaration on Forests and Land Use (COP26, 2021): Countries promised to halt and reverse forest loss by 2030. India did not sign it, objecting to the link with trade.
• Tropical Forest Forever Facility (TFFF): Launched by Brazil at the COP30 leaders' summit in Belém on 6 November 2025. It aims to build a fund of about $125 billion (around $25 billion from governments and philanthropies, used to attract about $100 billion of private money) and pay countries every year for each hectare of tropical forest they keep standing. Early pledges were well below the target.

Commonly confused concepts

• Carbon sink vs carbon stock: A sink is about the yearly flow (how much carbon is absorbed each year). A stock is the total carbon stored at one time. A forest can have a large stock but a shrinking sink.
• Carbon sink vs carbon source: A sink absorbs more than it releases; a source releases more than it absorbs. The same forest can switch between them in a drought or fire year.
• Deforestation vs degradation: Deforestation is clearing forest fully for another use. Degradation is when the forest remains but becomes thinner and weaker.
• Forest cover vs tree cover (India): Forest cover is all land over 1 hectare with tree canopy density above 10%, whoever owns it. Tree cover is patches of trees smaller than 1 hectare outside recorded forest.

Issues, criticism and the way forward

• Overestimating forests: Climate plans often assume forests will keep absorbing carbon at past rates. If the sink weakens, countries will need deeper emission cuts.
• Money gap: Payments to protect forests are small compared with the earnings from clearing them. REDD+ and the TFFF try to change this, but funding has been slow.
• Rights of forest people: Experts point out that indigenous and local communities protect forests well when their land rights are secure. In India, the Forest Rights Act, 2006 recognises such rights.
• Way forward: Cutting fossil fuel emissions is the main solution, because heat and drought come from global warming. Alongside, ending deforestation, controlling fires, restoring degraded land and better monitoring of forest health can protect the sink.

Concepts to Know

• Photosynthesis: The process by which green plants use sunlight, water and carbon dioxide to make food, releasing oxygen.
• Petagram (Pg): One billion tonnes. So 1.2 Pg of carbon means 1.2 billion tonnes.
• CO2-equivalent: A way of stating amounts of greenhouse gases, or carbon stored, in terms of the amount of carbon dioxide with the same warming effect.
• NDC (Nationally Determined Contribution): Each country's climate action plan and targets under the Paris Agreement.
• Savanna: Grassland with scattered trees, drier than a rainforest.