1. Topic 8.6 Greenhouse Effect
Global Warming
Topic 8.6
Greenhouse Effect

2. Remember…
The absorbed solar energy is re-radiated at longer wavelengths (in the infrared region of the spectrum)
Infrared
70%

3. Absorption by the Atmosphere
Various gases in the atmosphere can absorb radiation at this longer wavelength (resonance) H O
They vibrate more (become hotter) O
What happens to the gases when they absorb the radiation?
Vibrate more
Become hotter
No change
A & B C H H C H H H O

4. Greenhouse gases
These gases are known as “Greenhouse” gases. They include carbon dioxide, methane, water and N2O. O H O H H C H H C H O

5. Balance
There exists a balance between the energy absorbed by the earth (and its atmosphere) and the energy emitted.
Energy in
Energy out

6. Balance
This means that normally the earth has a fairly constant average temperature (although there have been big changes over thousands of years)
Energy in
Energy out

7. Balance
Without this normal “greenhouse effect” the earth would be too cold to live on.
Is the greenhouse effect good for us? Why?
Yes No
Energy in
Energy out

8. Bath balance
It’s a bit like trying to add water to a bath with the plug hole open.

9. Bath balance
The water reaches a certain level but no higher because the amount of water leaving eventually equals the amount entering

10. Bath balance
The water reaches a certain level but no higher because the amount of water leaving eventually equals the amount entering
Energy entering the earth
Earth’s temperature
Energy leaving the earth

11. Greenhouse gases
Most scientists believe that we are producing more of the gases that absorb the infrared radiation, thus upsetting the balance and producing a higher equilibrium earth temperature.

12. Bath with the plug half in!
This is like trying to fill a bath, but now with the plug half covering the hole.

13. A new balance
Eventually the water will reach a steady level again, but higher than before.
New HIGHER equilibrium temperature

14. What might happen?

15. Evidence? Ice core research Weather records
Remote sensing by satellites
Measurement!