The Greenhouse Effect and Earth's Energy Balance
- Earth’s climate is shaped by a delicate balance between incoming solar radiation and outgoing thermal radiation.
- This balance is influenced by greenhouse gases, which trap heat and regulate the planet’s temperature.
Key Greenhouse Gases and Their Sources
Definition
Greenhouse gas
A greenhouse gas is a gas that contributes to the greenhouse effect by absorbing infrared radiation
Greenhouse gases absorb and re-emit infrared radiation, warming Earth’s surface.
The most significant greenhouse gases are:
- Carbon dioxide (CO₂):
- Natural sources: Volcanic eruptions, respiration, and decomposition.
- Human sources: Burning fossil fuels, deforestation, and cement production.
- Methane (CH₄):
- Natural sources: Wetlands, termites, and oceans.
- Human sources: Agriculture (e.g., rice paddies, livestock), landfills, and fossil fuel extraction.
- Water vapor (H₂O):
- Natural sources: Evaporation from oceans, lakes, and rivers.
- Human sources: Irrigation and combustion processes.
- Nitrous oxide (N₂O):
- Natural sources: Soil processes and oceans.
- Human sources: Fertilizer use, fossil fuel combustion, and industrial activities.
Water vapor is the most abundant greenhouse gas, but its concentration is primarily controlled by temperature, not direct human activities.
Molecular Energy Levels and Infrared Radiation
Greenhouse gases interact with infrared radiation through absorption and emission processes.
Absorption of Infrared Radiation
- Molecules have discrete energy levels, including vibrational and rotational states.
- When infrared radiation matches the energy difference between these states, molecules absorb the photons, increasing their energy.
- CO₂ molecules can absorb infrared radiation by transitioning from a lower vibrational state to a higher one.
- This process is why CO₂ is an effective greenhouse gas.
