The Greenhouse Effect (HL IB Environmental Systems & Societies (ESS))
Revision Note
Greenhouse Gases & the Greenhouse Effect
Greenhouse gases (GHGs) and aerosols play an important role in Earth's climate by trapping heat in the atmosphere
Greenhouse gases and aerosols
GHGs: gases in the atmosphere that trap heat
Key GHGs:
Water vapour
Carbon dioxide
Methane
Nitrous Oxides
Aerosols: tiny particles or droplets in the atmosphere
Key aerosols:
Black carbon
A type of aerosol produced from incomplete combustion of fossil fuels, wood and other biomass
Found in emissions from, e.g. diesel engines, cooking stoves and open burning of vegetation
Absorbs sunlight and warms the atmosphere
Can darken snow and ice surfaces, reducing their reflectivity and accelerating melting
Key Greenhouse Gases
Name of GHG | Sources | Other Information |
|---|---|---|
Water vapour | Evaporation from oceans, lakes and rivers Transpiration from plants Sublimation from ice and snow Combustion of fossil fuels | Most abundant GHG Concentration varies with temperature Amplifies effects of other GHGs Positive feedback loop: warmer atmosphere holds more water vapour, leading to more warming and greater evaporation It is often excluded from climate models due to its dynamic levels and essential role in life, meaning it cannot be mitigated against |
Carbon dioxide | Burning fossil fuels: coal, oil and natural gas (e.g. vehicle emissions) Deforestation (when forests are cleared or burned, the carbon stored in trees is released back into atmosphere as carbon dioxide) Industrial processes (e.g. cement production) | Significant contributor to the greenhouse effect due to high concentration and long lifespan in the atmosphere |
Methane | Agriculture: livestock digestion (e.g. from large-scale cattle farming) Landfills Natural gas extraction (methane leaks) rice paddies Wetlands | More effective at trapping heat than carbon dioxide (over 20 times more potent over 100 years) Found in much lower concentrations than carbon dioxide, so overall warming effect is less |
Nitrous oxides | Agricultural practices (use of synthetic and organic fertilisers) Fossil fuel combustion Industrial processes | Potent GHG with a warming effect nearly 300 times that of carbon dioxide per molecule Found in much lower concentrations than carbon dioxide, so overall warming effect is less |
The Greenhouse Effect
What is the Greenhouse Effect?
The Sun emits energy in the form of solar radiation
This includes visible light and ultraviolet rays
This solar radiation enters the Earth’s atmosphere
Some thermal energy is reflected from the Earth's surface
Most thermal energy is absorbed and re-emitted back from the Earth’s surface
This energy passes through the atmosphere
Some thermal energy passes straight through and is emitted into space
However, some thermal energy is absorbed by greenhouse gases
This causes thermal energy to be re-emitted in all directions
These gases act like a blanket
They allow sunlight to pass through while preventing a significant amount of the infrared radiation from escaping back into space
This reduces the thermal energy lost into space and traps it within the Earth’s atmosphere
This keeps the Earth warm
This process is known as the greenhouse effect
The greenhouse effect is a naturally occurring phenomenon
The greenhouse effect is important to ensure that Earth is warm enough for life
Without the greenhouse effect, the average temperature would be much colder, making the planet uninhabitable
For example, the average surface temperature of Earth is about 15 °C
Without the greenhouse effect, it would be about -18 °C
Exam Tip
Don't get confused—the greenhouse effect is a natural process and is necessary for life on Earth. The accelerated or enhanced greenhouse effect refers to the changes in the greenhouse effect (mostly due to human activity) that are commonly referred to as global warming. This is discussed further in Causes of Climate Change.
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