Complex sentence: Historically the increase in energy consumption and the increase in energy efficiency were important historical causes of economic growth, and energy consumption remains highly correlated with economic growth, as is well noted in economic history and by the U. S. Dept. of Energy.
Split into simpler sentences: Historically the increase in energy consumption and the increase in energy efficiency were important causes of economic growth. Energy consumption remains highly correlated with economic growth, as is well noted in economic history and by the U. S. Dept. of Energy.