O - The greenhouse effect Flashcards
What does the greenhouse effect do?
Keeps us alive.
Explain the greenhouse effect
1) The Sun emits electromagnetic radiation, mostly visible light, UV radiation and infrared radiation.
2) When radiation from the Sun reaches the Earth’s atmosphere, most of the UV and infrared radiation is absorbed by atmospheric gases, and some radiation is reflected back into space from clouds.
3) The energy that reaches the Earth’s surface is mainly visible light and UV. Some of this radiation is reflected into space by light-coloured, shiny surfaces like ice and snow. The rest is absorbed by the Earth, which causes it to heat up.
4) The Earth then radiates energy back towards space as infrared radiation (heat).
5) Some of this IR radiation escapes (through the so-called ‘IR window’ - the range of iR frequencies that are not absorbed by atmospheric gases). But various gases in the troposphere (the lowest layer of the atmosphere) absorb other IR radiation and re-emit it in all directions - including back towards Earth, keeping us warm.
6) This is called the ‘greenhouse effect’.
7) Without this absorption and re-emission of heat by ‘greenhouse gases’, the average surface temperature on Earth would be about 30^oC cooler than it is - and we wouldn’t be here.
How can greenhouse gases transfer energy?
Through collisions.
What are the main greenhouse gases?
Water vapour, carbon dioxide and methane.
What is a greenhouse gas?
A gas whose molecules absorb IR radiation to make the bonds in the molecule vibrate more.
Explain how greenhouse gases can transfer energy through collisions
A greenhouse gas is a gas whose molecules absorb IR radiation to make the bonds in the molecule vibrate more.
This extra vibrational energy is passed on to other molecules in the air by collisions, giving the other molecules more kinetic energy and so raising the overall temperature.
Which greenhouse gas makes the greatest contribution to the greenhouse effect?
Water vapour.
What does the contribution of an particular gas to the greenhouse effect depend on?
- How much radiation one molecule of the gas absorbs.
- How much of that gas there is in the atmosphere (e.g. concentration in ppm).
Which greenhouse gas makes the smallest contribution to the greenhouse effect?
Methane.
What causes global warming?
An enhanced greenhouse effect.
What have we done to contribute to global warming?
- World’s population has increased rapidly and we’ve become more industrialised. To supply our energy needs, we’ve been burning fossil fuels at an increasing rate, releasing tons and tons of carbon dioxide into the atmosphere. We have also been chopping down forests which used to absorb CO2 for photosynthesis.
- Methane levels have risen as we have had to grow more food for our rising population. Cows are responsible for large amounts of methane
- These human activities have caused a rise in greenhouse gas concentrations, which enhances the greenhouse effect, since less IR can escape. So now too much heat is being trapped and the Earth is getting warmer.
How have human activities contributed to global warming?
These human activities have caused a rise in greenhouse gas concentrations, which enhances the greenhouse effect, since less IR can escape. So now too much heat is being trapped and the Earth is getting warmer.
What does global warming lead to?
Sea-levels rising and climate change.
What can cause climate change?
- Earth’s orbit changing (ice age cycles and interglacials).
- Changes in the Sun’s activity (sunspot cycles every 11 years)(global warming and cooling).
- Huge volcanic eruptions or meteor impacts throwing dust and smoke into the air (global cooling).
