Those atmospheric changes show up in the Earth's carbon balance, the team's model suggests. From 1960 through 1980, the researchers estimate, Earth's land plants stored about 440 million metric tons of carbon each year on average, but from 1980 to 1999 vegetation stored only 300 million metric tons annually.

Short-term variations in atmospheric aerosols, such as those seen in the wake of the eruption of Mount Pinatubo in the Philippines in 1991, triggered the same effect. In 1992 and 1993, land plants worldwide stored at least 1 billion metric tons of carbon more than they would have if the eruption hadn't occurred, the team's data suggest.

If pollution control measures continue to increase atmospheric clarity, the boost in natural carbon sequestration provided by diffuse radiation will abate to near zero by the year 2100, the researchers note.

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Editor:Yang Jie