While the Earth’s protective ozone layer is slowly healing from decades of damage from man-made chemicals, it’s unlikely to stabilize at pre-1980 levels, according to a University of Colorado researcher.
Naturally occurring ozone in the stratosphere protects plants and animals from the sun’s potentially harmful ultraviolet rays.
“We are not out of the woods yet, and the ozone recovery process still faces a number of uncertainties,” said Betsy Weatherhead, co-author of the study.
The findings were published in today’s edition of the journal Nature.
Scientists began to discover declines in ozone in the 1980s. Seasonal ozone levels declined as much as 70 percent over Antarctica, 30 percent over the Arctic and 3 percent worldwide.
The ozone declines led to a 1987 international agreement, known as the Montreal Protocol, banning ozone-depleting chemicals such as chlorofluorocarbons.
The new study, by Weatherhead and Signe Bech Andersen of the Danish Meteorological Institute, concludes that the ban is helping heal the ozone layer.The researchers said that by the end of the century, ozone levels could be close to pre-1980 levels.
Among the uncertainties, Weatherhead said, is global warming.
Research shows warmer temperatures at the Earth’s surface can trigger colder conditions in the lower stratosphere and promote the formation of polar stratospheric clouds, which can trigger severe ozone depletion.
“It’s certainly one of those factors that can affect ozone levels over the long run,” Weatherhead said.
She said future ozone levels probably will be dominated by air temperature, atmospheric dynamics and trace gases, such as those containing significant amounts of nitrous oxide, a result of fertilizer production.
“In another 50 years, chlorofluorocarbons won’t be the dominant factor controlling ozone,” Weatherhead said. “Instead, we think it will be factors like greenhouse gases, nitrous oxide and methane.”
Volcanic activity also has an impact on ozone levels. The 1993 eruption of Mount Pinatubo in the Philippines caused ozone levels to backslide for several years, Weatherhead said.
For the study, Weatherhead and Andersen analyzed ozone data collected by NASA and National Oceanic Atmospheric Administration satellites and ground stations.
The new study follows a 2005 study led by Weatherhead that determined the ozone layer was no longer shrinking following nearly two decades of depletion from man-made chemicals.
“Since the full recovery of the ozone layer is probably decades away, the amount of ultraviolet radiation is likely to remain elevated for some years,” she said. “People still need to take precautions when spending time in the sun.”
Staff writer Kim McGuire can be reached at 303-820-1240 or kmcguire@denverpost.com.
