Existing technology can derive enough energy from renewable sources to meet the world's needs several times over, according to a Worldwatch Institute report released in January. (For an assessment of the practical aspects, see “The Power of Renewables,” by Matthew L. Wald, on page 56.) The report also summarizes the fourth assessment of the Intergovernmental Panel on Climate Change and the policies needed to survive a warmer world.

Trillions of kilowatt-hours of global energy used annually: 132.5

Years this amount would power a U.S. home: 13 billion

Trillions of kilowatt-hours of energy that can, in principle, be harvested with current technology:

Solar: 444

Wind: 167

Geothermal: 139

Biomass: 69

Percent of global energy used:

By buildings: 40

For electricity generation: 41

Percent of global energy generated from renewable sources, including hydropower: 20

Fraction of energy wasted as heat during electricity generation: 2/3

SOURCE: State of the World, 2009