Contributions of weather and fuel mix to recent declines in U.S.energy and carbon intensity

A recent (1996-2000) acceleration of declines in energy andcarbon intensity in the U.S. remains largely unexplained. This study usesDivisia decomposition and regression to test two candidate explanations -fuel mix and weather. The Divisia method demonstrates that fuel mix doesnot explain the declines in carbon intensity. The fuel mix, both overalland for electricity generation, became slightly more carbon intensiveover the study period (though the slight trend reversed before the end ofthe period). A regression-based correction to the Divisia indices,accounting for variation in heating- and cooling-degree-days, indicatesthat warmer weather accounts for about 30 percent ofthe total declines.This leaves declines of more than 2 percent per year (and an accelerationof more than 1 percent over previous decade) remaining to beexplained