Efforts to reduce the levels of ozone-depleting chemicals in the air has apparently not caused any appreciable difference in the size of the ozone hole above the Antarctic, new research says.

More to the point, yearly changes in the South Pole's ozone hole are likely due to natural variations in wind patterns, scientists have announced during the annual meeting in San Francisco of the American Geophysical Union, expected to attract more than 22,000 scientists from throughout the world.

The findings suggest measuring the diameter of the ozone hole in fact reveals little about ozone depletion, and likewise it's misleading to assess improvements to the environment based on the hole's size alone.

People won't be able to see the ultimate impact of reducing ozone-eating chemicals in the atmosphere until around 2025, the research team said, adding the hole won't be completely close until about 2070.

Ozone is a molecule made up of oxygen atoms and the ozone layer ranges between 12 to 19 miles (20 to 30 kilometers) above the earth's surface, protecting life on the planet by shielding it from ultraviolet (UV) radiation.

"Ozone is produced in the tropics, but it's transported by the winds from the tropics to the polar region," which "varies a little bit from year to year," said Anne Douglass, a scientist with the Aura project at NASA's Goddard Space Flight Center in Greenbelt, Md.

The scientific community generally believes the widespread use of chlorofluorocarbons (CFCs) for refrigerants and aerosols through the early 1990s created an ozone hole in the earth's stratosphere, above Antarctica.

Ozone is depleted by CFCs, which bind to oxygen molecules in several chemical reactions, and break them down into basic oxygen molecules.

The Montreal Protocol was an international agreement, first signed in 1987, which set usage caps for CFCs and eventually phased out the use of them altogether.

In 2012, the ozone hole shrank to record lows, although the level of CFCs in the atmosphere hadn't declined dramatically, said study co-author Natalya Kramarova, also from NASA Goddard.

On the other hand, the ozone hole in 2011 was about as big as it was in 2006, even though the use of CFCs was significantly reduced over that five-year period.

Kramarova took a closer look at data collected by the Suomi National Polar-orbiting Partnership satellite, which analyzed ozone levels at various altitudes, and discovered the smaller size of the ozone hole in 2012 was a result of weather bringing in more ozone at higher levels of the stratosphere than usual to Antarctica, masking the depletion at lower levels.

In another study, researchers used the Aura satellite's Microwave Limb Sounder to examine the inside of the ozone hole by measuring the levels of chemicals such as nitrous oxide, which change inversely with levels of chlorine in the atmosphere, a byproduct of CFCs..

The researchers found in 2011 that chlorine levels were lower despite the ozone hole growing bigger in size. Then, using a computer model, they showed weather conditions would have lowered the amount of ozone over Antarctica regardless of the presence of CFCs and that the bigger hole resulted from tropical winds carrying less ozone to the area than in previous years.

Said study co-author Susan Strahan, a NASA Goddard atmospheric chemist: "This is a meteorological effect. It has nothing to do with chemistry,"