9.3 Notes on the Greenhouse Effect

9.3 The Greenhouse Effect

Solar Radiation

  • Not all incoming solar radiation interacts with Earth's surface.

    • Reflected Radiation:

      • 26% of solar radiation is reflected back into space by:

        • Clouds

        • Atmosphere

    • Absorbed Radiation:

      • 19% is absorbed by the atmosphere and clouds and then radiated out into space.

    • The remainder of the solar radiation reaches Earth’s surface, where it can be absorbed or reflected, depending on the surface's albedo.

      • Albedo: A measure of how much light that hits a surface is reflected without being absorbed.

        • Darker Surfaces:

          • Lower albedo

          • Absorb more sunlight, converting it to heat, which we feel as warmth.

        • Lighter Surfaces:

          • Higher albedo

          • Reflect more sunlight directly back into space or towards clouds and greenhouse gases (GHGs).

The Greenhouse Effect

  • The greenhouse effect is a natural process in Earth's atmosphere that traps heat from the Sun, preventing it from escaping back into space, thereby keeping the planet warm enough to sustain life.

    • Without the Greenhouse Effect:

      • Earth would be too cold to support life as we know it.

How the Greenhouse Effect Works:

  1. Solar Radiation:

    • Solar radiation from the Sun, including light waves such as ultraviolet (UV) and visible light, heats the Earth's surface.

  2. Infrared Radiation:

    • The Earth's surface releases energy in the form of infrared radiation.

  3. Absorption by Greenhouse Gases:

    • Greenhouse gases (GHGs) present in the atmosphere absorb some of this infrared radiation.

  4. Radiation Back to Earth:

    • The absorbed infrared radiation is then re-radiated back towards the Earth's surface, contributing to the greenhouse effect.

    • This re-radiation helps maintain the Earth's temperature and supports various ecological systems.

Greenhouse Gases and Their Sources

  • The most important greenhouse gases (GHGs) are:

    • Carbon Dioxide (CO₂):

      • Major sources include:

        • Fossil fuel combustion

        • Decomposition of organic materials

        • Deforestation

Greenhouse Gases and Their Global Warming Potential (GWP) - Global warming potential (GWP) measures how much heat a greenhouse gas traps in the atmosphere over a specific time frame, typically 100 years, compared to carbon dioxide (CO₂). - The following greenhouse gases are listed from least GWP to greatest GWP:

  1. Carbon Dioxide (CO₂): GWP = 1

  2. Methane (CH₄): GWP ≈ 28-36 (over 100 years)

  3. Nitrous Oxide (N₂O): GWP ≈ 298

  4. Hydrofluorocarbons (HFCs): GWP varies depending on the specific type, ranging from around 124 to more than 12,000, with some HFCs having very high GWPs like HFC-23 (GWP ≈ 12,400)

  5. Perfluorocarbons (PFCs): GWP varies but can be in the range of 7,390 to 12,200

  6. Sulfur Hexafluoride (SF₆): GWP ≈ 22,800