With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.

With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

Consuming the largest amount of energy, space heating accounts for 31% of all residential energy used. Space cooling accounts for an additional 12% of energy usage.

Consuming the largest amount of energy, space heating accounts for 31% of all residential energy used. Space cooling accounts for an additional 12% of energy usage.

Consuming the largest amount of energy, space heating accounts for 31% of all residential energy used. Space cooling accounts for an additional 12% of energy usage.

As of 2014, the very best experimental units could convert more than 40% of light energy to electricity; ordinary commercial units are in the range of 5% to 20%. 

As of 2014, the very best experimental units could convert more than 40% of light energy to electricity; ordinary commercial units are in the range of 5% to 20%. 

As of 2014, the very best experimental units could convert more than 40% of light energy to electricity; ordinary commercial units are in the range of 5% to 20%. 

Most direct uses of primary energy are limited to generating heat and motion. Electricity, by contrast, is extremely versatile, with a wide range of complex applications. 

Most direct uses of primary energy are limited to generating heat and motion. Electricity, by contrast, is extremely versatile, with a wide range of complex applications. 

On average, a typical coal-burning power plant in 2013 was about 33% efficient in converting heat energy into electrical power. A gas-fired plant was about 42% efficient. And in natural gas combined-cycle power plants—in which waste heat from a natural gas turbine is used to power a steam turbine—generation may be as much as 60% efficient.

On average, a typical coal-burning power plant in 2013 was about 33% efficient in converting heat energy into electrical power. A gas-fired plant was about 42% efficient. And in natural gas combined-cycle power plants—in which waste heat from a natural gas turbine is used to power a steam turbine—generation may be as much as 60% efficient.

Biofuels contain carbon and although they may burn “cleaner” than oil-derived fuels, they do not avoid generating carbon dioxide emissions.

CO2 concentration in the atmosphere has risen about 43% since the beginning of the industrial revolution in the mid-eighteenth century-half of that since 1980

CO2 concentration in the atmosphere has risen about 43% since the beginning of the industrial revolution in the mid-eighteenth century-half of that since 1980

CO2 concentration in the atmosphere has risen about 43% since the beginning of the industrial revolution in the mid-eighteenth century-half of that since 1980

Wood and waste biomass, along with biofuels, accounted for about 50% of the U.S. renewable energy supply in 2014, and more than 4% of all energy consumed. 

Wood and waste biomass, along with biofuels, accounted for about 50% of the U.S. renewable energy supply in 2014, and more than 4% of all energy consumed. 

Wood and waste biomass, along with biofuels, accounted for about 50% of the U.S. renewable energy supply in 2014, and more than 4% of all energy consumed.