SULFUR HEXAFLUORIDEPotent man-made greenhouse gas used as an insulator in switches and transformers on the electrical grid. Reported emissions are declining, but amounts in the atmosphere are going up.
METHANEEmitted by everything from peat bogs to landfills, cattle ranches, and coal mines. Measurements show atmospheric levels can be higher than the sum of reported emissions.
CARBON DIOXIDEComes from natural sources and burning fossil fuels. Reported and actual levels are now fairly close, but researchers worry that putting a high price on carbon could be an incentive to under-report.
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