Global dimming — the 100-word-version

A handy rebuttal to the science-challenged handwringers you're stuck with through New Year's Day. Slate's Green Lantern columnist Brendan Koerner has boiled down the facts on global dimming. It turns out to be global brightening, except in India and China. I pared Koerner's piece even further to one snappy paragraph.

A scary 2005 BBC documentary overplayed the doomsday angle. The planet has actually gotten brighter over the past 15 years. The term "global dimming" refers to the reduction of solar radiation hitting the planet's surface, caused by the proliferation of aerosols in the atmosphere. Though industrial soot plays a role, nothing affects sunlight like an erupting volcano. Since 1991, when the eruption of Mount Pinatubo caused the Earth to get much dimmer for about two years, there has been an overall brightening trend. According to NASA worldwide aerosol levels in 2005 were 20 percent off their late 1980s peak. But the amount of sunlight hitting each square yard of Chinese soil has declined by 3.7 watts in the past 50 years; India has experienced a similar decrease. The two nations' surge in aerosol-producing economic activity hasn't been accompanied by regulations to control emissions. Aerosols may actually mask global warming at the planet's surface, but recent research shows the brown cloud over Asia is heating up the lower atmosphere from approximately 6,500 to 16,500 feet. That's bad news for the Himalayan glaciers, which are melting at a rapid clip.

(Photo by Steve Locke)