By Sid Perkins
The decline in the solar radiation reaching Earth’s surface in the latter half of the 20th century—a trend observed at many locations worldwide for several decades—turns out to have been primarily a regional phenomenon, new research suggests.
On average, about 342 watts of solar radiation strike each square meter at the top of Earth’s atmosphere. As much as one-third of that radiation immediately bounces back into space. A small amount gets absorbed within the atmosphere. The rest—about two-thirds of the total—arrives at the planet’s surface.