"If you go to the beach these days, you're at slightly higher risk of getting skin cancer (without protection)," Herman said, though he noted the risk would have been even greater in the absence of regulations on ozone-depleting substances.
Last year, one of Herman's Goddard colleagues, Paul Newman, published a study showing that the ozone hole likely would have become a year-round fixture and UV radiation would increase 650 percent by 2065 in mid-latitude cities if not for the Montreal Protocol, an international treaty signed in 1987 that limited the amount of ozone-depleting gases countries could emit.
Clouds and Hemispheric Dimming
In addition to analyzing ozone and ultraviolet trends, Herman also used satellite data to study whether changes in cloudiness have affected UV trends. To his surprise, he found that increased cloudiness in the southern hemisphere produced a dimming effect that increased the shielding from UV compared to previous years.
In the higher latitudes especially, he detected a slight reduction typically of 2 to 4 percent -- in the amount of UV passing through the atmosphere and reaching the surface due to clouds. "It's not a large amount, but it's intriguing," Herman said. "We aren't sure what's behind it yet."
Vitali Fioletov, a Canadian scientist and member of the World Meteorological Organization's advisory group on ultraviolet radiation, agreed that Herman's findings about cloudiness warrant additional investigation. "I found the cloud effects on the global scale to be the most interesting aspect of the study," he said. "This isn't something you could see without satellites."
Herman synthesized measurements from the Total Ozone Mapping Spectrometer (TOMS) aboard Nimbus 7 and Earth Probe, the Ozone Monitoring Instrument (OMI) on
|Contact: Sarah Dewitt|
NASA/Goddard Space Flight Center