WORLD TEMPERATURE-TREND UNCERTAINTIES AND THEIR IMPLICATIONS FOR ECONOMIC-POLICY

Three data sets on world temperature are studied. Data on direct measu rements of world temperature over the past century yield trend estimat es of .45 degrees Celsius per century with rather wide confidence inte rvals of (.15,.75). The data's behavior raises questions about whether the trend is genuine or due to greenhouse-gas emissions. Data on temp erature measurements inferred from tree rings over the past 1,500 year s display no trend. The upward drift over the past century could easil y be a cyclical upswing of the type that has occurred many times in th e past.