Environmental Science
Carbon Cycle
Quick fact
The carbon cycle moves about 200 billion tonnes of carbon between the atmosphere, land, and oceans every year, yet only a tiny fraction remains in the air at any moment.
Why this is interesting
Every time you breathe out, you release carbon dioxide into the air. But where does that carbon go next? The answer reveals a planetary balancing act essential for life itself.
Read the full explanation
Understanding Carbon Cycle
Think of the carbon cycle as Earth's carbon currency: carbon atoms are constantly exchanged between different 'accounts'—the atmosphere, oceans, soil, living things, and rocks. Plants are the primary 'depositors,' taking carbon dioxide from the air during photosynthesis to build their tissues. Animals and other organisms are 'withdrawers,' releasing carbon dioxide through respiration and decomposition. Over millions of years, dead organisms can become fossil fuels, storing carbon underground. When we burn those fuels, we return ancient carbon to the atmosphere rapidly, upsetting the balance.
A deeper explanation
The carbon cycle operates through biological, geological, and chemical processes. Photosynthesis fixes inorganic carbon from CO₂ into organic molecules, while respiration and decomposition reverse this. The ocean absorbs CO₂ from the atmosphere, forming carbonic acid—a process that helps regulate atmospheric levels but also causes ocean acidification. Geological processes, such as volcanic eruptions and the weathering of rocks, move carbon over long timescales. This intricate system has kept Earth's climate stable for millennia, but human extraction and combustion of fossil fuels have added billions of tonnes of carbon to the atmosphere annually, intensifying the greenhouse effect and driving climate change.