Possible Clues:

• The Greens are always going on about this diamond - it's a clue for the detective
• Environmental impact factor
• Stepping out of the fireplace, Santa left a __
• Copy and measure picture's emissions
• Engine part, when running, has to mark emission level
• Measure of environmental impact
• One�s fuel consumption is about right? Sadly no on trip to Belgium and France
• From measure of energy usage, black mark put down?
• How to track down a supplier of fossil fuels?
• Walking into motor oil company, runs into reduced cost of fossil fuel