The greenhouse effect

  • The sun emits electromagnetic radiation

  • Most of this radiation reaches the Earth as visible or UV

  • The Earth’s surface absorbs some of this energy which causes it to heat up

  • The Earth radiates infrared radiation back out towards space

  • Some of the IR radiation escapes through the IR window (range of IR frequencies that are not absorbed by greenhouse gases)

  • Various gases in the troposphere absorb IR radiation and re-emit it in all direction, including back toward the Earth, heating it up

Greenhouse gases

  • The main greenhouse gases are:

    • Water vapour

    • Carbon dioxide

    • Methane

  • These molecules absorb IR radiation which makes the bonds in the molecules to vibrate more

  • This extra vibrational energy is transferred to other molecules by collisions, increasing their kinetic energy and raising the overall temperature

  • The contribution of a greenhouse gas to the greenhouse effect depends on:

    • How much radiation one molecule of the gas absorbs

    • The concentration of the gas in the atmosphere

Enhanced greenhouse effect

  • As the human population has increased, the demand for energy has increased

  • This leads to the increased burning of fossil fuels which releases a lot of carbon dioxide into the atmosphere

  • The demand for timber and paper has also lead to an increase in deforestation meaning there are less trees to absorb this excess CO2

  • Increased farming has lead to increased levels of methane in the atmosphere as cows release methane

  • This increased concentration of greenhouse gases in the atmosphere means that less IR radiation escape resulting in an enhanced greenhouse effect

  • Too much heat is being trapped and this causes global warming and climate change

Climate change

  • Climate change is a natural process

    • E.g. regular changes in the Earth’s orbit around the sun are linked to ice age cycles

    • E.g. changes to the sun’s activity

    • E.g. volcanic eruptions and meteor impacts