The Greenhouse Effect What is the greenhouse effect?

natural greenhouse effect http://www. elmhurst Greenhouse Analogy: Energy from the sun in the form of some ultraviolet and visible light (short wavelength) passes through the glass of the greenhouse. As the light strikes various surfaces in the greenhouse they are heated. These surfaces in turn re-radiate the heat in the form of infrared radiation (long wavelength). However, the IR radiation is blocked from escaping by the glass. IR is not able to pass through the glass, hence the greenhouse air heats up fairly dramatically. The greenhouse gases have the same property as the glass towards the IR radiation. Think of the greenhouse gases acting as an invisible glass shield around the earth.

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

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

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.

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

                                                                                                   

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.

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

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

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

If this didn’t happen… The climate would be an average of 60°F colder and the earth could not sustain life as we know it.

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

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

Greenhouse gas molecules are able to vibrate with the absorption of heat

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

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.

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.

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?

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

greenhouse gases definition Greenhouse gases are gases that: allow visible light and UV radiation (short-wavelength/high frequency) to pass through them but (because of the nature of their covalent bonds in their molecules) absorb the infrared radiation (longer-wavelength radiation) of the same frequency as the one the Earth converts the energy from the Sun into and reradiates this infrared radiation back to the Earth.

Greenhouse factor Compares ability of a greenhouse gas to absorb IR to the same amount of carbon dioxide which has a factor of 1. Example: greenhouse factor of methane is 30 which means it absorbs as much as 30 molecules of carbon dioxide or 1 molecule of methane absorbs 30 times more as 1 molecule of carbon dioxide.

greenhouse gas: CO2 Sources: Human: burning fossil fuels and wood, forest fires, burning waste Natural: respiration, decay of organic matter, natural forest fires Relative effect: Most important greenhouse gas (50% contribution) because of its great abundance (second largest after water vapour) and the large range of wavelengths over which it absorbs IR.

Greenhouse gases: H2O Sources: Human: combustion of hydrocarbons Natural: evaporation Relative effect: 0.1 - Least effective in trapping radiation but is most abundant.

Greenhouse gases: CH4 Sources: Human: cattle farming, rice paddies (wet soil means any organic matter in it is decomposed without oxygen) , petroleum and natural gas production. Natural: digestive tracts of ruminants, cattle, bogs or marshes, bacterial fermentation – when organic matter is decomposed anaerobically, methane gas is produced. Relative effect: 30 - Low abundance in atmosphere but it is more effective in absorbing infrared radiation, however, its atmospheric lifespan in the atmosphere is short.

Greenhouse gases: N2O Sources: Human: use of nitrogen based fertilizers Natural: bacterial action Relative effect: 150 - Very effective in absorbing radiation, fairly long atmospheric life.

Greenhouse gases: CFCs Sources: Human: refrigerators, air- conditioning, aerosols in spraying cans, foaming agents Natural: none!!!! Relative effect: 10 000 – 25 000 - Very effective in absorbing radiation, long atmospheric life but low abundance.

Greenhouse gases: SF6 Human source: electrical insulators Greenhouse effect: 24 000

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

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

Effects of particulates particulates scatters and reflect the incoming sunlight (visible and UV) so that less solar radiation enters the atmosphere; particulates also cause a lowering of the temperature as they provide condensation nuclei around which water particles condense to form clouds reducing solar heating; volcanic eruptions and large forest fires greatly increase the amount of particulates.  

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

terminology greenhouse effect = the absorbing of some of the infra-red radiation radiated from the Earth in the atmosphere which is then reradiated back to Earth; this results in… global warming = a gradual increase in planet-wide temperatures

Global warming effects (1) World wide rise in sea levels resulting from: Partial melting of glaciers and polar ice caps Thermal expansion of water (as a result of heating). Changes in crop yields: some crops will grow better, other worse.

Global warming effects (2) Changes in distribution of commercial crops Changes in the distribution of pests and disease-carrying organisms e.g. malaria. More severe weather conditions: floods in particular of coastal areas; more severe storms e.g. monsoon floods in Pakistan 2010 More severe droughts e.g. 2010 worst drought in Amazon

Global warming: evidence global temperatures since 1850s http://www What can the mean global temperature anomaly be used for? This product is a global-scale climate diagnostic tool and provides a big picture overview of average global temperatures compared to a reference value.

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.

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.

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.

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.

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.

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!