of 21
5/27/2018 Effect of Greenhouse Gases
1/21
5/27/2018 Effect of Greenhouse Gases
2/21
CARBON DIOXIDE
METHANE
WATER VAPOUR
NITROUS OXIDE
5/27/2018 Effect of Greenhouse Gases
3/21
5/27/2018 Effect of Greenhouse Gases
4/21
Radiation from the sun is absorbed by the earth asradiant visible light.
You feel this effect on a sunny day when you stand inthe sunshine vs. the shade.
Eventually, the heat from the earth is re-emitted intothe atmosphere as infrared radiation (IR).
The different types of electromagnetic radiation areshown in the graphic.
5/27/2018 Effect of Greenhouse Gases
5/21
5/27/2018 Effect of Greenhouse Gases
6/21
Certain gases in the atmosphere have the property ofabsorbing infrared radiation.
Oxygen and nitrogen, the major gases in theatmosphere do not have this property.
The infrared radiation strikes a molecule such ascarbon dioxide and causes the bonds to bend andvibrate - this is called the absorption of IR energy.
The molecule gains kinetic energy by this absorptionof IR radiation.
This extra kinetic energy may then be transmitted toother moleculessuch as oxygen and nitrogen andcauses a general heating of the atmosphere.
5/27/2018 Effect of Greenhouse Gases
7/21
5/27/2018 Effect of Greenhouse Gases
8/21
Energy from the sun in the form of some ultravioletand visible light (short wavelength) passes through the
glass of the greenhouse. As the light strikes various surfaces in the greenhouse
and they are heated. These surfaces in turn re-radiatethe 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 propertyas theglass towards the IR radiation. Think of thegreenhouse gases acting as an invisible glass shieldaround the earth.
5/27/2018 Effect of Greenhouse Gases
9/21
5/27/2018 Effect of Greenhouse Gases
10/21
The greenhouse gas molecules are shown along withthe IR spectra and the bending and vibrations caused
by absorbing the IR radiation.
The arrows on the molecules indicate the direction ofthe bends and vibrations of the bonds.
The IR spectra indicates the specific energies at certainwavelengths which are absorbed. Radiation that is
100% transmittance is not blockedbut travels straightthrough the sample.
5/27/2018 Effect of Greenhouse Gases
11/21
5/27/2018 Effect of Greenhouse Gases
12/21
The greenhouse effect is a vital factor in keepingour planet warm enough for us to live on it.
5/27/2018 Effect of Greenhouse Gases
13/21
The Sun emits electromagnetic radiation mostly asvisible light, UV radiation and infrared (IR) radiation.
When this solar radiation reaches the Earthsatmosphere the UV and IR radiation is mostly
absorbed by atmospheric gases and some is reflectedback into space from clouds.
5/27/2018 Effect of Greenhouse Gases
14/21
Visible light, IR and UV radiation reaching the Earthssurface can be reflected back into space (especiallyfrom light-coloured surfaces such as snow) but the rest
is absorbed by the Earth, which heats up. The Earth radiates energy back out to space as IR
radiation (heat).
Gases in the atmosphere can absorb some of this IR
radiation and re-emit it in all directions. Some getsback to Earth again and keeps us warm.
5/27/2018 Effect of Greenhouse Gases
15/21
This is called the greenhouse effect because gases inthe atmosphere act like the glass in a greenhouse,
trapping some of the energy. If this didnt happen andalmost all the energy was lost to space, the Earthwould be about 30C cooler and we wouldnt be able tolive here.
5/27/2018 Effect of Greenhouse Gases
16/21
Definition: Gases which contribute to the greenhouseeffect are called greenhouse gases and are classified
according their relative greenhouse factors. This termallows a comparison of the effect they will have onglobal warming. It is calculated by comparing theeffect gases have in absorbing IR radiation relative tothe effect of carbon dioxide, the most common
greenhouse gas. The global warming potential of a gasis calculated by combining their relative greenhousefactor (ability to absorb IR radiation) and their half-lifein the atmosphere (how long they take to break
down). It is a better measure of the true effects ofreleasing a gas into the atmosphere over its wholelifetime.
5/27/2018 Effect of Greenhouse Gases
17/21
The table below shows the relative greenhouse factorand the global warming potential for some of the most
common greenhouse gases.
5/27/2018 Effect of Greenhouse Gases
18/21
5/27/2018 Effect of Greenhouse Gases
19/21
Determined by :
Their ability to absorb infrared radiationExpressed in watts per square meter (W/m2)
Radioactive forcing also expressed in (W/m2)
It depends on: The potency of the gas or the greenhouse strength
The amount of increase in that gas in the atmosphere
Methane is much more potent than carbon dioxide
Carbon dioxide increase greater in quantity in Earths atmosphere.
Net effect of global warming in carbon dioxide is thrice great in case for
methane.
5/27/2018 Effect of Greenhouse Gases
20/21
Their half-life in Earths atmosphereGreenhouse gases will disappear from the atmosphere at their specific
lifetime of half-life. Water vapor tends to cycle out of the atmosphere in a matter of days.
Thus, it has a small global warming potential
Methane takes over 12 years to disappear from the atmosphere.
Carbon dioxide takes centuries!As the carbon dioxide is the reference gas, therefore its GWP is precisely 1.
Over 100 year of period, GWP of methane is much reduced 23. eventhough methane is much potent but methane is short-lived. Thus resultsto offset to total contribution of global warming.
BUTsome FLUOROCARBONS has GREATER POTENCY and LONGERLIFETIME. Released in large quantities of these GHG some sort will causelong term of earth global warming and thus resulting to climate change .
5/27/2018 Effect of Greenhouse Gases
21/21
