How do you turn a concept into a logo

Recently we were asked to create a new logo for Emission Traders International.
Their old logo was more of a diagram than a logo and would only be understood by the cognoscenti. 
Most people would have no idea about how emission trading works, but they would probably think the following

• It's good for the planet
  
• It has to do with cleaning the air
  
• It has to do with trading something dirty for something clean
  
• It involves plants and trees and the atmosphere
  
• It works between countries around the globe
  

Our job as designers was to take that information and distill it into a symbol that represented the essence of what emission trading is all about.
The final logo we produced symbolised the following information.

• Circular movement, through a cycle, from dark and dirty to light and clean.
  
• A circle, suggesting wholeness and the blue planet
  
• New plant growth from dark to light and upwards

Needless to say our client was delighted with the result which is now on all of the newly designed corporate stationery and about to make it's way onto a revamped website.

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