UPSC Prelims 2021 Q19: What Is Blue Carbon? — Explained
What is blue carbon?
- Carbon captured by oceans and coastal ecosystems
- Carbon sequestered in forest biomass and agricultural soils
- Carbon contained in petroleum and natural gas
- Carbon present in atmosphere
Answer: (a) Carbon captured by oceans and coastal ecosystems
Statement-wise explanation
- a: correct — Blue carbon is the carbon that ocean and coastal ecosystems capture and store. Most of it is held in mangroves, salt marshes and seagrass meadows. IUCN defines it as 'the carbon stored in coastal and marine ecosystems'. The term became widely used after the 2009 rapid response assessment 'Blue Carbon' by UNEP, FAO and IOC-UNESCO.
- b: incorrect — Carbon held in forest biomass and agricultural soils is on land. It is commonly called 'green carbon'. Agroforestry and soil-carbon farming are ways to increase it, but these are land-based sinks, not marine or coastal ones.
- c: incorrect — Petroleum and natural gas hold fossil carbon. It formed from organic matter buried over millions of years, and burning it adds carbon to the atmosphere. Blue carbon is a living, biological sink that removes carbon now. Fossil fuels are a source of carbon, not a sink.
- d: incorrect — Carbon in the atmosphere, mostly as CO2 and methane, is what carbon sinks take up. Blue carbon is carbon after it has been removed from the air and locked into coastal vegetation and sediments. It is not carbon that is still in the air.
How to eliminate
Look at the colour in the name. 'Blue' points to water: oceans and coasts. Only one option mentions water. Forests and farm soils are land systems ('green carbon'). Petroleum and gas are fossil stores. Atmospheric carbon is not stored anywhere. So basic knowledge is enough here: if you know that UPSC uses colour labels (blue, green, black, brown) for carbon, you can answer at once. Remember this: blue carbon means mangroves, salt marshes and seagrass meadows. Most of their carbon is in waterlogged soils.
Know more
Blue carbon is carbon captured by living coastal and marine organisms and stored in coastal ecosystems. There are three core habitats: mangroves, salt (tidal) marshes and seagrass meadows. Some sources also include kelp forests.
Why these habitats matter:
- NOAA estimates that mangroves and coastal wetlands sequester carbon about 10 times faster than mature tropical forests. They store 3–5 times more carbon per unit area.
- Most of this carbon is in the soil, not the plants. Waterlogged soils with little oxygen slow decomposition, so buried carbon can stay for hundreds or thousands of years.
- When these habitats are cleared or degraded, for example for aquaculture ponds or ports, the stored carbon is released as CO2. The 2009 UNEP–FAO–IOC-UNESCO report estimated that up to 7% of blue carbon sinks are lost each year.
- The same habitats protect coasts. They buffer storm surges and reduce erosion, and they serve as fish nurseries. This is why they are central to ecosystem-based adaptation.
The 'colours' of carbon UPSC uses:
| Term | What it means |
|---|---|
| Blue carbon | Carbon stored in coastal and marine ecosystems |
| Green carbon | Carbon stored in land plants and soils (forests, grasslands, farm soils) |
| Black carbon | Soot from incomplete burning of fossil fuels and biomass; a short-lived climate pollutant |
| Brown carbon | Light-absorbing organic aerosol, mainly from burning biomass |
India link: India's mangroves are mainly in the Sundarbans, Bhitarkanika, the Godavari–Krishna delta, Gujarat's Kachchh coast and the Andaman & Nicobar Islands. Seagrass beds are found in the Gulf of Mannar and Palk Bay. India's MISHTI scheme (launched in 2023) plants mangroves along the coast. India is also a member of the Mangrove Alliance for Climate.
In the news
The UN Decade of Ocean Science for Sustainable Development and the UN Decade on Ecosystem Restoration both began in 2021. In February 2021 the Ministry of Earth Sciences released a draft Blue Economy policy for public comment. Both kept ocean- and coast-based climate solutions in the news before the 2021 Prelims.
NCERT Concepts to Revise
- Blue carbon: The question asks for the exact meaning of this term, so its precise scope decides between the four options.
- Carbon sink: Every option describes a carbon store or pool; knowing what makes something a sink helps separate stores from sources.
- Mangrove: Mangroves are a key coastal habitat that comes up whenever ocean and coastal carbon storage is discussed.
- Agroforestry: Agroforestry is a land-based way to store carbon in trees and farm soils, the kind of storage one option describes.