Explain carbon emission and absorption in nature.
The Carbon Cycle is the continuous movement of carbon atoms between the atmosphere, oceans, land, and living organisms. In nature, carbon is constantly being released (emission) and taken up (absorption) through various biological, chemical, and physical processes, maintaining a dynamic equilibrium that has been disrupted by human activities.
Photosynthesis: 6CO2 + 6H2O + Light → C6H12O6 + 6O2
Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
| Sink | Mechanism | Carbon Stored |
|---|---|---|
| Photosynthesis | Plants convert CO2 to glucose using sunlight | ~120 Gt C/year absorbed |
| Forests | Trees store carbon in wood, leaves, roots | ~450 Gt C in biomass |
| Soil | Organic matter, humus, peat accumulation | ~1,500 Gt C (top 1m) |
| Grasslands | Root systems store carbon underground | 30% of terrestrial carbon |
Ocean's Role: Oceans absorb approximately 25% of human CO2 emissions annually (~10 Gt CO2), making them the largest active carbon sink. However, this causes ocean acidification (pH drop from 8.2 to 8.1 since industrialization).
| Reservoir | Carbon Content (Gt C) | Exchange Rate |
|---|---|---|
| Atmosphere | ~870 | Fast (days to years) |
| Oceans | ~38,000 | Medium (decades to centuries) |
| Terrestrial Biosphere | ~2,000 | Fast (seasonal to decades) |
| Soil | ~1,500 | Slow (decades to centuries) |
| Fossil Fuels | ~4,000 | Very slow (millions of years) |
Before industrialization, natural emissions and absorptions were roughly balanced:
Key Statistic: Human activities add ~40 Gt CO2/year to the natural carbon cycle. Natural sinks absorb only ~50% (~20 Gt), leaving the rest to accumulate in the atmosphere.
In nature, carbon continuously cycles between atmosphere, land, and oceans through processes like photosynthesis, respiration, decomposition, and ocean exchange. For millennia, natural emissions and absorptions remained balanced, maintaining stable atmospheric CO2 levels. However, human activities - primarily fossil fuel combustion and deforestation - have disrupted this balance by adding approximately 40 Gt CO2 annually to the cycle. Since natural sinks can only absorb about half of these emissions, excess carbon accumulates in the atmosphere, driving climate change. Protecting and enhancing natural carbon sinks (forests, oceans, soils) is essential for climate mitigation alongside emission reductions.