Ozone layer
The greenhouse gases:
 The following table shows the other ‘greenhouse’ gases. They have contributed to the ‘enhanced’ greenhouse effect, through their impact on the ozone in the upper atmosphere. The impact of ozone itself is hard to quantify and scientifically uncertain. Chlorofluorocarbons (CFCs) are   the strongest greenhouse gas per molecule. However, their low concentrations in the   atmosphere mean that they are less relevant to the production of the enhanced greenhouse effect. 
Holes in the ozone layer
CFCs also affect the ozone layer in the upper atmosphere that protects temperatures on Earth by blocking ultraviolet rays from the sun. There have been reports of  enlarged holes in the ozone layer of the atmosphere over the North and South   Poles. That, and a general decline in global stratospheric ozone levels, has caused many nations to cutback on their production and use   of these chemicals. In 1987, the signing of the
 enlarged holes in the ozone layer of the atmosphere over the North and South   Poles. That, and a general decline in global stratospheric ozone levels, has caused many nations to cutback on their production and use   of these chemicals. In 1987, the signing of the  Montreal Protocol by forty-six nations established an immediate timetable   for the global reduction of CFC production and use. As a result, the levels of CFC's in the atmosphere peaked in 1995 and have been falling have started to fall. The holes may even be
 Montreal Protocol by forty-six nations established an immediate timetable   for the global reduction of CFC production and use. As a result, the levels of CFC's in the atmosphere peaked in 1995 and have been falling have started to fall. The holes may even be  starting to recover.
 starting to recover.
	
	
	
		
			
    
      | Gas | Conc (ppm)
 | Average time spent in atmosphere (years) | Source | Why it has increased | 
      
      | 03Ozone
 | 0.01-0.05 | Unknown | Car exhausts | More fossil fuels for transporrt | 
    
      | CFCsChlorfluro-
 carbons
 | 0.003 | 55-116 | CoolantsPropellants
 Expanders (foams)
 | More refrigerators etc. (Montreal Protocol has banned use of CFCs in developed countries. | 
		
			
	
	 
	 The effects of climate change
 The effects of climate change
	
	 
		
		
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