Carbon sinks and sources

Forests

Forests and soils have a role in the amount of carbon dioxide (CO₂) in the atmosphere. CO₂ is removed from the atmosphere by plants during photosynthesis and returned to the atmosphere by respiration of plants, animals and soil microbes, and fires. As climate change makes the Earth warmer, there are more forest fires, which releases carbon back into the atmosphere as CO₂.

Oceans

Oceans also exchange carbon with the atmosphere. CO₂ from the air dissolves into the ocean’s surface where it is used by plants and animals. CO₂ is also released from the ocean’s surface. Too much carbon in the ocean can damage plants and animals as it makes the water more acidic. Climate change is also causing the ocean to get warmer, meaning it can store less CO₂.

Fossil fuels

Fossil fuels are a large source of CO₂ in our atmosphere. They are burnt by humans, and unlike the forest and ocean sources, fossil fuels do not have a compensating sink.

Fossil fuels such as coal, gas and petrol are mostly made of carbon and formed from the buried remains of ancient organisms (hence the name ‘fossil’ fuels!). These fossil fuels are burnt to produce electricity, power and heat. As humans have burnt fossil fuels, more and more carbon has been added to the atmosphere and oceans instead of being stored deep underground. People are adding carbon into the atmosphere faster than it can be removed.

Some other natural sources of CO₂ in the atmosphere are the weathering of rocks and volcanoes erupting. When the magma rises to the surface of a volcano and erupts, the carbon dioxide escapes into the air, which is a natural geological process, but this contribution is still much smaller compared to human activities like burning fossil fuels.

Related articles

• COVID-19 and greenhouse gas emissions
• The Southern Ocean’s ecological richness and significance for global climate
• The rock cycle
• Non-renewable energy sources
• The ocean and the carbon cycle
• Carbon cycle
• Carbon dioxide in the ocean
• Carbon dioxide in the atmosphere
• Alternative conceptions about fossil fuels

Related activities

• Ocean acidification and eggshells
• Carbon cycle quiz

Related media

• Increasing atmospheric carbon dioxide – video
• Southern Ocean carbon sink – video
• Carbon dioxide exchange – video
• Oil formation – animation
• Carbon cycle – interactive

Useful link

• Feedback – School Journal Level 4 2020