Increased CO2 levels in the atmosphere are correlated with rising global temperatures, leading many scientists to believe that the first phenomenon has caused the second. What would it take to be certain that this correlation represents a cause-and-effect relationship?
A controlled experiment in which all other vari-ables are held constant would be required. A reduction in global CO2 levels followed by a decrease inglobal temperatures would support the idea ofcause-and-effect relationship.