Carbon Cycle

This lesson covers: 

1. Why living organisms need carbon
2. The processes involved in the carbon cycle
3. Daily, seasonal, and annual fluctuations in atmospheric carbon dioxide levels

An overview of the carbon cycle

Carbon is found in all organic molecules, including fats, carbohydrates, and proteins. It is a fundamental component of almost all major molecules found in living organisms.

The carbon cycle demonstrates the continuous movement of carbon between the biotic (living) and abiotic (non-living) components of the environment.

There are several key processes involved in the carbon cycle:

• Photosynthesis - Producers, like plants, absorb CO₂ from the atmosphere and convert it into organic molecules.
• Consumption - Carbon is passed through food chains as organisms consume other organisms.
• Respiration - Organisms use oxygen and carbohydrates to release energy, releasing CO₂ back into the atmosphere.
• Decomposition - Dead organic matter is broken down by microorganisms, which releases CO₂ into the environment.
• Formation of fossil fuels - Carbon, stored in dead organic matter that does not decompose due to high temperature and pressure, is transformed over millions of years into fossil fuels, including coal and oil.
• Combustion - The burning of fossil fuels reacts stored carbon with oxygen, releasing CO₂ into the atmosphere.
• Weathering - Carbon stored in sedimentary rocks is released back into the environment through weathering processes.
• Volcanic activity - Tectonic plate movements can lead to the release of CO₂ from volcanic eruptions.

Fluctuations in atmospheric carbon dioxide

Atmospheric CO₂ levels fluctuate on a daily, seasonal, and annual basis, mainly due to variations in photosynthesis and respiration rates.

Daily fluctuations in atmospheric CO₂:

• Respiration occurs continuously throughout the day and night, releasing CO₂ into the atmosphere.
• Photosynthesis only occurs during daylight, removing CO₂ from the atmosphere and reducing local atmospheric CO₂ levels during the daylight hours.

Seasonal fluctuations in atmospheric CO₂:

• During the summer, long daylight hours and warm temperatures increase photosynthesis rates, absorbing more CO₂ and reducing local atmospheric CO₂ levels.
• During winter, reduced daylight hours and colder temperatures decrease photosynthesis rates and resulting in higher local atmospheric CO₂ levels.

Annual fluctuations in atmospheric CO₂:

• Annually, greenhouse gas emissions, including those of CO₂, have been increasing.
• Increased deforestation removes photosynthesising biomass, lowering the capacity to remove CO₂ from the atmosphere.
• Deforestation often involves burning the biomass of trees, which releases additional CO₂ into the atmosphere.
• The rising concentration of CO₂ in the atmosphere accelerates global warming.
• Global warming decreases the solubility of carbon dioxide in oceans as less gas can dissolve in warmer water, leading to more CO₂ being released into the atmosphere.