Scientists took a look inside the ozone hole that forms over Antarctica every year, and found the dropping concentrations of chlorine in the stratosphere have not helped repair the damage.
Two decades ago the Montreal Protocol provided an agreement for ozone-depleting substances to be limited, a NASA Goddard Space Flight Center news release reported.
The effort stopped the growth of the ozone hole in its tracks, but researchers are yet to see any recovery.
"Ozone holes with smaller areas and a larger total amount of ozone are not necessarily evidence of recovery attributable to the expected chlorine decline," Susan Strahan of NASA's Goddard Space Flight Center, said. "That assumption is like trying to understand what's wrong with your car's engine without lifting the hood."
In 2012 the hole was the smallest it had been since the 1980s. The team used satellite data to get an idea of what was going on inside the ozone hole, they used this information to compile a "map" that showed how thick the ozone had been at various altitudes through the season.
The team found the 2012 ozone hole was "more complex" than they had expected it to be. They observed that an increase of ozone at higher altitudes was carried by wind and ended up right above the region of ozone destruction.
"Our work shows that the classic metrics based on the total ozone values have limitations -- they don't tell us the whole story," Natalya Kramarov of NASA Goddard said.
The "classic metrics" indicates that the idea the ozone hole has started to heal is only an illusion. Meteorology may have been wholly responsible for the smaller hole; meaning levels of ozone-harming substances are also higher than we thought.
A separate study led by Strahan looked at data from NASA's Aura satellite's Microwave Limb Sounder to track nitrous oxide levels. The gas has an inverse relationship with ozone-damaging chlorine.
The researchers observed that the 2006 and 2011 ozone holes contained different levels of chlorine, but were basically equal in severity.
The team found during the 2011 hole there was less ozone destruction than in 2006 because wind patterns transferred less ozone to the Antarctic, meaning there was less to lose in the first place.
"This was a meteorological, not chemical effect. In contrast, wind blew more ozone to the Antarctic in 2006 and thus there was more ozone destruction," the news release reported.
The recent study primarily proved current methods of measuring ozone destruction and repair tend to be inaccurate.
The researchers also concluded that chlorine levels in the lower stratosphere will not decline to below the where it was in the 1990s until between 2015 and 2030. The levels are not expected to drop enough for ozone repair until the late 2030s.
"We are still in the period where small changes in chlorine do not affect the area of the ozone hole, which is why it's too soon to say the ozone hole is recovering," Strahan said. "We're going into a period of large variability and there will be bumps in the road before we can identify a clear recovery."
