1. The Greenhouse Effect
What is the greenhouse effect?

2. gases in the atmosphere
Earth
Greenhouse gases are present in the atmosphere surrounding the earth

3. The sun emits ultraviolet (UV) radiation which hits the earth
In the form of light that we can see

4. These rays of light hit the earth and reflect back towards space in the form of UV as well as Infrared (IR) radiation
IR Radiation is a form of energy that we can’t see.

5. gases in the atmosphere pick up some of the heat from the IR rays and disperse them back into the earth’s atmosphere keeping the earth warm enough to sustain life

6. Would you be able to feel the heat?
To clarify what IR Radiation is: Stoves, hotplates and fires are all forms of IR Radiation. The heat waves are emitted even though you can’t see them. There isn’t necessarily any light emitted but there is heat.

7. On a molecular level…
This increases the kinetic energy of other molecules and raises the average temperature of the atmosphere. What part of the molecule has become excited? (answer: the electron have higher vibrational energy levels) Greenhouse gases let the UV light through and only react to the IR radiation.
When certain gases in the atmosphere absorb IR Radiation their vibrational modes are excited and vibrate, causing them to collide with other molecules and transfer energy

8. When the electrons return to their ground state, they re-emit the energy with a frequency equal to the frequency of energy gap between the two levels

9. Only certain gases do this, just like dogs can hear frequencies that humans cannot because their eardrum vibrates with different wavelengths than ours

10. If this didn’t happen…
The climate would be an average of 33°C colder and the earth could not sustain life as we know it.

11. So greenhouse gases are called greenhouse gases because they keep some heat in the atmosphere to sustain life on earth as a greenhouse does to sustain life in the greenhouse when it is cold outside

12. So a round of applause for greenhouse gases !

13. Let’s find out which atmospheric gases are green house gases

14. Hint…
Greenhouse gas molecules are able to vibrate with the absorption of heat

15. So why do greenhouse gases have such a bad reputation?
It is not only because some of them don’t smell so good!

16. Natural Versus Enhanced
Climate chemists believe that humans are producing more of the naturally occurring greenhouse gases than the atmosphere can naturally handle from…
Increased meat production which produces more methane, increased fossil fuel burning which creates increased CO2

17. Anthropogenic
Climate scientists are for the most part agreed that the climate is generally heating up but most think that humans are creating an enhanced greenhouse effect through their actions – we call this anthropogenic. Caused by human actions. Anthropogenic effects, processes or materials are those that are derived from human activities, as opposed to those occurring in biophysical environments without human influence.

18. The most abundant atmospheric gas, Nitrogen molecules have a strong bond which makes it chemically stable and non-reactive in most circumstances. Nitrogen's simple structure is unable to absorb either visible or infrared light. As a result, nitrogen is not a greenhouse gas.

19. Oxygen is the second most abundant atmospheric gas
Oxygen is the second most abundant atmospheric gas. Why do you think that Oxygen is also not a greenhouse gas?

20. The IR radiation is of the correct frequency to be
absorbed by the electrons in the C=O bonds in carbon dioxide, O-H bonds in water
and C-H bonds in methane, causing them to vibrate, bend, rock, scissor and twist (for
example). IR radiation causes bonds in certain gas molecules to vibrate. This is due to a change in dipole momentThis is not true when you have three molecules, as the center of charge moves as the molecule vibrates, creating a dipole moment. For carbon dioxide, you can have a symmetric vibration (this acts like the diatomic molecules and so is not infrared active), but you can also have the asymmetric fashion, in which one bond shortens while the other lengthens. There is also the bending mode, and different vibrations correspond to absorption at different wavelengths . Only gases with more than one nucleus absorb infrared radiation

24. there are others
Have students complete the worksheet here

25. Some greenhouse gases are not naturally occurring – they are manmade
Carbon tetrafluoride
Sulfur Hexafluoride
Hexafluoroethane

26. And Hydrofluorocarbons Which once saved the earth!
Hydrofluorocarbons were developed to replace CFCs and helped solve the problem of the hole in the ozone layer unfortunately…These replacement chemicals act like “super” greenhouse gases, with a heat-trapping power that can be 4,470 times that of carbon dioxide.

27. CFC’s or Chlorofluorocarbons
CFCs came from amongst other things aerosols and were banned from use in 1970 because they were found to be creating a hole in the ozone layer. Chemists sprang into action to invent a better way to perform the same job as CFCs

28. UV light in the atmosphere would break thte bonds of the Chlorine in the CFC’s and release it. Chlorine was found to deplete the ozone.

29. HFC – Hydrofluorocarbons was the answer
Hydrofluorocarbons replaced CFC’s. Which part did they take out just from reading the name ? They are commonly manufactured for refrigeration/air-conditioning, foam blowing, general aerosols, metered dose inhalers (MDIs), solvent cleaning and fire fighting. Unfortunately, Hydrofluorocarbons have large global warming potentials (GWP) thousands of times more powerful than CO2.

30. Right now HFC’s do not contribute to climate change as much as CO2 but…
As the world becomes more developed and more people in the world have cooling systems, refrigerated foods and produce insulating foams, this could change rapidly. This will be most evident in the developing world.

31. Chemists to the rescue!
We need more chemists to look at ways to solve these problems. Here is one success story – read the article about Ben and Jerry’s non HFC refrigerator.

32. Why should I care??????
Because the earth will not die – life as we know it will die and that is all about you! Explain to students that issues of the environment are really about the flourishing of human life as they know it. The earth and some sort of ecosystem is likely to survive as it did in previous ice ages etc. What will die off are life forms. Probably Humans first!