UV Exposure Has Increased Over the Last 30 Years, but Stabilized Since the Mid-1990s
NASA scientists analyzing 30 years of satellite data have found that the amount of ultraviolet (UV) radiation reaching Earth's surface has increased markedly over the last three decades. Most of the increase has occurred in the mid-and-high latitudes, and there's been little or no increase in tropical regions.
The new analysis shows, for example, that at one line of latitude — 32.5 degrees — a line that runs through central Texas in the northern hemisphere and the country of Uruguay in the southern hemisphere, 305 nanometer UV levels have gone up by some 6 percent on average since 1979.
The primary culprit: decreasing levels of stratospheric ozone, a colorless gas that acts as Earth’s natural sunscreen by shielding the surface from damaging UV radiation.
The finding reinforces previous observations that show UV levels are stabilizing after countries began signing an international treaty that limited the emissions of ozone-depleting gases in 1987. The study also shows that increased cloudiness in the southern hemisphere over the 30-year period has impacted UV.
Jay Herman, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., stitched together data from several earth observing satellites — including NASA's Aura satellite, NOAA weather satellites, and commercial satellites — to draw his conclusions. The results were published in the Journal of Geophysical Research in February.
"Overall, we're still not where we'd like to be with ozone, but we're on the right track," said Jay Herman. "We do still see an increase in UV on a 30-year timescale, but it's moderate, it could have been worse, and it appears to have leveled off."
In the tropics, the increase has been minimal, but in the mid-latitudes it has been more obvious. During the summer, for example, UV has increased by more than 20 percent in Patagonia and the southern portions of South America. It has risen by nearly 10 percent in Buenos Aires, a city that's about the same distance from the equator as Little Rock, Ark. At Washington, D.C.'s latitude — about 35 degrees north — UV has increased by about 9 percent since 1979. ...
