Greenhouse gases are gases in Earth’s atmosphere that trap heat. They let sunlight pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere.
This natural process is essential for maintaining the planet’s temperature, making it habitable. However, human activities have significantly increased the concentrations of these gases, enhancing the greenhouse effect and contributing to global climate change.
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What are the key Greenhouse Gases?
The key greenhouse gases are:
- Carbon Dioxide (CO₂)
- Methane (CH₄)
- Nitrous Oxide (N₂O)
- Industrial Gases or the Fluorinated Gases
- Hydrofluorocarbons (HFCs) / Hydrofluorocarbon-23 (HFC-23)
- Perfluorocarbons (PFCs) / Chlorofluorocarbon-12 (CFC-12)
- Sulfur hexafluoride (SF₆)
- Nitrogen trifluoride (NF₃)
- Water Vapor (H₂O)
- Ozone (O₃)
Carbon Dioxide (CO₂)
Sources: Burning fossil fuels (coal, oil, natural gas), deforestation, cement production.
Impact: The most significant long-lived greenhouse gas emitted by human activities. It accounts for the majority of global greenhouse gas emissions.
Methane (CH₄)
Sources: Agriculture (especially livestock), natural gas and petroleum systems, landfills, and wetlands.
Impact: More effective at trapping heat than CO₂ but has a shorter atmospheric lifetime.
Nitrous Oxide (N₂O)
Sources: Agricultural activities (use of fertilizers), industrial processes, combustion of fossil fuels and biomass.
Impact: Has a long atmospheric lifetime and a significant warming potential.
Industrial Gases or the Fluorinated Gases
Types: Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃).
Sources: Industrial applications, refrigeration, air conditioning, and electronics manufacturing.
Impact: Extremely potent greenhouse gases with high global warming potentials, though present in smaller concentrations.
Other greenhouse gases
Other greenhouse gases not counted in U.S. or international greenhouse gas inventories are water vapor and ozone.
Water vapor is the most abundant greenhouse gas, but most scientists believe that water vapor produced directly by human activity contributes very little to the amount of water vapor in the atmosphere. Therefore, the U.S. Energy Information Administration (EIA) does not estimate emissions of water vapor.
Ozone is technically a greenhouse gas, but ozone can be helpful or harmful, depending on where it is in the earth’s atmosphere.
Water Vapor (H₂O)
Sources: Naturally occurring through evaporation and transpiration.
Impact: The most abundant greenhouse gas, but its concentration is largely controlled by natural processes and is considered a feedback mechanism rather than a direct driver of climate change.
Ozone (O₃)
Contributes to the greenhouse effect in the lower atmosphere (troposphere).
Results from chemical reactions involving sunlight, vehicle emissions, and industrial pollutants.
The Greenhouse Effect
The greenhouse effect occurs when greenhouse gases absorb infrared radiation emitted by the Earth’s surface and re-radiate it in all directions, including back towards the surface. This process traps heat in the atmosphere, keeping the planet warm enough to support life. Without the natural greenhouse effect, Earth’s average temperature would be about -18°C (0°F) instead of the current +15°C (59°F).
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