Greenhouse Gases (GHGs)
A Greenhouse Gas (GHG) is any gas in the atmosphere that absorbs and re-emits infrared radiation (heat), thereby trapping heat and warming the planet's surface. This natural phenomenon, called the Greenhouse Effect, is essential for life on Earth, maintaining the average global temperature at a livable level.
However, human activities (like fossil fuel burning and deforestation) have dramatically increased GHG concentrations, leading to an enhanced greenhouse effect—the main driver of global warming and climate change.
The Greenhouse Effect: How the atmosphere traps outgoing heat.
How the Greenhouse Effect Works
- Incoming Energy: The Sun emits short-wave solar radiation that mostly passes through the atmosphere and reaches Earth's surface.
- Absorption & Re-emission: The surface absorbs this energy and re-radiates it as long-wave infrared heat.
- Heat Trapping: GHG molecules absorb some of this heat and re-radiate it in all directions, creating a “heat blanket” around the Earth.
Distinction: Water Vapor vs. Carbon Dioxide
⚠️ Largest Contributor vs. Main Driver
Water Vapor (H2O): The largest contributor (36%–70%) to the natural greenhouse effect. It acts as a feedback gas: more warming → more evaporation → more H2O → stronger warming.
Carbon Dioxide (CO2): The primary driver of the enhanced greenhouse effect, since its concentration is controlled by human emissions. CO2 sets the baseline temperature that water vapor feedback amplifies.
Relative contribution of major human-caused Greenhouse Gases to the enhanced greenhouse effect (excluding water vapor feedback)
Major Greenhouse Gases and Key Information
| Gas | Primary Anthropogenic Sources | Atmospheric Lifetime | Global Warming Potential (GWP) |
|---|---|---|---|
| Water Vapor (H2O) | (Natural Feedback; Not directly controlled by emissions) | Days to Weeks (Very Short) | N/A |
| Carbon Dioxide (CO2) | Burning fossil fuels (coal, oil, gas), deforestation, cement production. | Decades to Centuries (Long) | 1 (Reference Gas) |
| Methane (CH4) | Fossil fuel extraction, livestock (enteric fermentation), landfills, rice cultivation. | ~12 years (Short-lived, but potent) | ~28x greater than CO2 |
| Nitrous Oxide (N2O) | Use of nitrogen-based fertilizers in agriculture, fossil fuel combustion. | ~109 years (Very Long) | ~265x greater than CO2 |
| Fluorinated Gases (F-gases) | Industrial processes, refrigeration, aerosols, electrical equipment. | Decades to Thousands years | Thousands of times greater than CO2 |
Impacts of the Enhanced Greenhouse Effect
- Global Warming: Long-term rise in Earth's average temperature.
- Sea Level Rise: From melting ice sheets and thermal expansion of seawater.
- Ocean Acidification: Excess CO2 dissolving in oceans, damaging coral reefs & shells.
- Extreme Weather: More intense storms, floods, droughts, and heatwaves.