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.
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