At Last Count: 4,000,000
That's how many wind turbines would be required to produce 7.5 terawatts of power—enough to supply more than half of the world's energy needs in 2030, according to a study by Mark Jacobson, professor of civil and environmental engineering at Stanford, and Cristina Archer, associate professor of geography and physical ocean science and engineering at the University of Delaware. Jacobson and Archer would place half of the turbines over water. The remaining 2 million would require a little more than one-half of 1 percent of the Earth's land surface.
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Data is from the past two weeks.