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UV exposure has increased over the last 30 years, reveals satellite data | 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. "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," he added.
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. Despite the overall increases,
there are clear signs that ultraviolet radiation levels are on the verge of falling.
Herman's analysis, which is in agreement with a World Meteorological Report published
in recent years, shows that decreases in ozone and corresponding increases in
UV irradiance leveled off in the mid-nineties.
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