Energy Intensity
Energy intensity improvements have provided enormous reductions in energy requirements over the last fifty years. Over the course of the post-world war two era (1949 to 2000) U.S. energy intensity declined at an average annual rate of 1.3 percent per year, with a comparable reduction in carbon intensity observed over the same period. Over this period cumulative U.S. emissions were 58 billion metric tons of carbon. Without the improvement in energy intensity, emissions would have been 80 billion metric tons of carbon with the same GDP growth. Energy intensity improvements therefore accounted for cumulative emissions reductions of 22 billion metric tons of carbon in the U.S. alone over this period. These reductions were the result of a combination of improvements in the efficiency of individual energy-using devices (e.g. lighting, and motors), changes in the energy intensity of industrial processes (e.g. the substitution of plastics for steel in vehicles), and shifts in consumer demand away from energy intensive products toward lower energy intensity products such as services.
While the longer-term, historical relationship between energy and GDP shows a similar pattern when both commercial and non-commercial energy forms are considered over century time scales, the same is not true for commercial energy alone. The historical relationship between commercial energy and GDP shows an increase in energy intensity during early periods of economic development, followed by a peak and long-term decline. This relationship reflects a systematic substitution of high energy density commercial products for low energy-density, labor-intensive, traditional biomass fuels. Scenarios of the future in which energy intensity improvement is the largest single source of emissions reduction anticipate a continuation of such relationships throughout the 21st century. These reductions are predicated on the assumption that the underlying sources of technological improvements that provided the means by which historical reductions were achieved will continue. The goal of the deep dive in energy intensity is to explore that assumption-to decompose aggregate energy intensity improvements and assess the conditions necessary to attain assumed levels of reference scenario energy-intensity improvements and to accelerate this trend over century time scales.