from the EUV-from-above dept.
NASA and the US National Oceanic and Atmospheric Administration have been monitoring the ozone hole since it was first discovered in 1985. The agencies use satellites, weather balloons and ground-based instruments to study and track the hole. The ozone hole changes throughout the year and reached its 2017 peak size on Sept. 11 at the end of the region's wintertime.
Scientists weren't surprised by the size of the hole this year. "This is what we would expect to see given the weather conditions in the Antarctic stratosphere," says Paul A. Newman, a scientist at NASA's Goddard Space Flight Center. NASA cites warmer global temperatures as a factor in reducing the hole.
But don't get too excited. NASA says the smaller hole "is due to natural variability and not a signal of rapid healing." The ozone hole still covered 7.6 million square miles (nearly 20 million square kilometers), or over two and a half times the size of Australia. Still, scientists are optimistic about the ozone hole eventually healing over time.
The ozone layer may be recovering above Antarctica, but not over the equator:
Thirty years after nations banded together to phase out chemicals that destroy stratospheric ozone, the gaping hole in the earth's ultraviolet (UV) radiation shield above Antarctica is shrinking. But new findings suggest that at mid-latitudes, where most people live, the ozone layer in the lower stratosphere is growing more tenuous--for reasons that scientists are struggling to fathom.
"I don't want people to panic or get overly worried," says William Ball, an atmospheric physicist at the Physikalisch-Meteorologisches Observatorium Davos World Radiation Centre in Switzerland. "But there is something happening in the lower stratosphere that's important to understand."
Several recent studies, including one published last month in Geophysical Research Letters, point to a robust recovery of stratospheric ozone concentrations over Antarctica--the long-awaited payoff after the Montreal Protocol in 1987 mandated a global phase-out of chlorofluorocarbons (CFCs) and other ozone-eating compounds.
But recent evidence indicates that the global campaign to mend the ozone layer is far from over. In an analysis published today in Atmospheric Chemistry and Physics, Ball and colleagues combined satellite data to examine ozone at mid-latitudes, from Earth's surface on up through the troposphere and the stratosphere. They found that from 1998 to 2016, ozone in the lower stratosphere ebbed by 2.2 Dobson units--a measure of ozone thickness--even as concentrations in the upper stratosphere rose by about 0.8 Dobson units. "We saw it at almost every latitude and every altitude below about 25 kilometers," Ball says. "That made us very concerned that perhaps this was something very real that no one looked at before."
Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery (open, DOI: 10.5194/acp-18-1379-2018) (DX)
Previously: Ozone Layer Hole at its Smallest Size Since 1988