Atmospheric warming

 

Atmospheric warming

Greenhouse ​gases

A greenhouse gas is a gas that absorbs and emits radiation in the infrared range.  The main  greenhouse gases in the Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone.

Without greenhouse gases, the Earth's surface would average about -19 oC instead of 14 oC.

Contribution of each gas/vapour to atmospheric warming

Gas
 
Formula
 
Contribution
(%)
Water vapor H2O 36 – 72%  
Carbon dioxide CO2 9 – 26%
Methane CH4 4 – 9%  
Ozone O3 3 – 7% 

Source: Wikipedia

Warming due to greenhouse gases

A guitar string, or a closed pipe, will resonate at exact frequencies. It is the same with molecules. Each photons is a packet of electromagnetic radiation of specific frequency. If a frequency is the same as any of the resonant frequencies of the molecule, then the molecule will vibrate and warm the surrounding molecules by re-emitting the radiation in a random direction .

Carbon dioxide (above), water vapor, methane, nitrous oxide, and a few other gases are greenhouse gases. They all are molecules composed of more than two component atoms, bound loosely enough together to be able to vibrate with the absorption of heat. In O2, N2, H2, the (moderate) vibration of the two atoms does not entail any movement of charge, so no absorption or emission of electromagnetic radiation.

The peak of the thermal IR emission from the Earth's surface is very close to a strong vibrational absorption band of CO2, 67 cm−1.

 

 

Each molecule that can vibrate due to elastic bonds between it's atoms, will do so at its own frequencies. Those frequencies are absorbed and re-emittted producing characteristic spectra.

Warming by water vapour

The amount of water vapour in the atmosphere depends on temperature, and how much water there is available to be evaporated.

Warming by greenhouse gases, increases the amount of water vapour, thus producing a positive feedback effect that increases temperature even more.

The average residence time of a water molecule in the atmosphere is only about nine days.

Small technical detail..

Air does not hold water vapour, it coexists with it. At say 20 oC, the water vapour above a pool of water will be the same in a vacuum, or an atmosphere of any gases.

Meet the molecules

This table is from: http://chemistry.beloit.edu/Warming/pages/molecule.html  



Atmospheric Sampling Sites

 


Click to rotate molecule

 


Concentration Units (Click to see graph)

 


Global Warming Potential*

 


Atmospheric lifetime (years)*
Carbon dioxide
CO2

 


 


ppm

 


1

 


120
Methane
CH4

 


 


ppb

 


25

 


12
Hydrogen
H2

 


 


ppb
   
Nitrous oxide
N2O

 


 


ppb

 


298

 


114
Carbon monoxide
CO

 


 


ppb
~2

0.25

Trichlorofluoromethane
CCl3F
CFC-11

 


 


ppt

 


4,750

 


45
Dichlorodifluoromethane
CF2Cl2
CFC-12

 


 


ppt

 


10,900

 


100

Trichlorotrifluoroethane
CCl2FCClF2

CFC-113

 


 


ppt

 


6,130

 


85
Carbon tetrachloride
CCl4

 


 


ppt

 


1,400

 


26
Chloroform
CHCl3

 


 


ppt

 


30

 


0.51
Dichloromethane
CH2Cl2

 


 


ppt

 


8.7

 


0.38
Methyl chloride
CH3Cl

 


 


ppt
13
1.0
Tetrachloroethene
Cl2C=CCl2
Perchloroethylene (perc)

 


 


ppt
   
Methyl chloroform
CH3CCl3

 


 


ppt

 


146

 


5

Chlorodifluoromethane
CHClF2

HCFC-22

 


 


ppt

 


1,810

 


12
Chlorodifluoroethane
CH3CClF2
HCFC-142b

 


 


ppt
2,310
17.9

Dichlorofluoroethane
CH3CFCl2

HCFC-141b

 


 


ppt
725
9.3

Difluoroethane
CH3CHF2

HFC-152a

 


 


ppt
124
1.4

Tetrafluoroethane
CH2FCF3
HFC-134a

 


 


ppt
1,430
14

Fluoroform
CHF3
HFC-23

 


 


ppt
14,800
270
Perfluoroethane
CF3CF3
PFC-116

 


 


~ 4 ppt

 


12,200

 


10,000

Bromochlorodifluoromethane 
CBrClF2
Halon-1211

 


 


ppt

 


1,890

 


16

Methylbromide 
CH3Br

 


 


ppt

 


5

 


0.7
Dibromotetrafluoroethane 
CBrF2CBrF2
Halon-2402

 


 


ppt

 


1,640

 


20
Bromotrifluoromethane
CBrF3
Halon-1301

 


 


ppt

 


7,140

 


65
Sulfur hexafluoride
SF6

 


 


ppt

 


22,800

 


3,200
Trifluoromethyl sulfur pentafluoride
CF3SF5

 


 


ppt

 


17,700

 


800
Nitrogen trifluoride
NF3

 


 


ppt

 


17,200

 


740
Carbon tetrafluoride
CF4

 


 


~80 ppt

 


7,390

 


50,000

 

 

ppm = parts per million (106), ppb = parts per billion (109), ppt = parts per trillion (1012).

* The Global Warming Potential (GWP) is used to contrast different greenhouse gases and provides a simple measure of the radiative effects of various greenhouse gases relative to CO2 defined as 1. Atmospheric lifetime is used to characterize the decay of an instanenous pulse input to the atmosphere, and represents the time the input would take to decay to 0.368 (1/e) of its original value. One hundred year time horizon GWPs and atmospheric lifetimes taken from Table 2.14, Intergovernmental Panel on Climate Change, Climate Change 2007: The Physical Science Basis, IPCC WG1 AR4 Report. See also http://cdiac.esd.ornl.gov/pns/current_ghg.html

References

 


    Discovery of global warming