Today’s electric system is almost unrecognizable from the electric system a decade ago. Generation from natural gas and renewables has accelerated to replace the rapid and unprecedented retirement of coal-fired generators. Wind, solar, and geothermal electric generating capacity in the United States has now eclipsed capacities from hydroelectric and nuclear resources combined. Carbon dioxide (CO₂) emissions have reached their lowest levels since 1987. Meanwhile, both total generation and electric sales have held relatively steady for 10 years.