The hole in the ozone layer of the atmosphere that forms right over Antarctic every year is as small as it has been since 1988, NASA announced on Thursday. But even so, that doesn’t mean that emissions are necessarily down.

The scientists involved in studying the hole found that the warm air in the stratosphere caused the ozone hole to be “exceptionally weak,” says a release from NASA. The ozone depletes more quickly in colder temperatures, so when temperatures during the winter time in the southern hemisphere are warmer, the hole reaches a lower annual maximum at the end of the season than it would after a colder winter season. So with a warmer winter 2017 season, the hole reached a seasonal maximum far smaller than any hole that has formed in previous years, including 2016. however, researchers don’t think lower level of depletion exhibited this year is a sign of healing for the layer, just a symptom of natural variability in weather.

What is the ozone and why is it important?

The ozone layer is actually part of the Earth’s stratosphere layer of the atmosphere. In that layer, which stretched from six to 30 miles above the surface of the Earth, the chemical compound ozone absorbs radiation from the sun, more specifically it absorbs the ultraviolet radiation that cause be especially harmful to lifeforms.

Ozone has been depleted by chemically active bromine and chlorine that was released into the atmosphere abundantly before regulations were put in place in 1987. That regulation lowered the amount of the ozone-depleting chemicals allowed into the atmosphere but the chlorofluorocarbons, or CFCs, are still making their way through the stratosphere and have a very long lifespan, so the hole is still larger than when it was first detected in the 80s.

Even though there have been warmer years recently making for a smaller hole in the ozone than usual, the hole is still there, millions of miles in area, letting in radiation from outer space that the Earth was previously protected from. That radiation can cause cancer, cataracts, suppress immune systems and damage the vegetation on Earth, according to NASA.

The hole is measured using several technologies from NASA and the National Oceanic and Atmospheric Administration. Those include several satellites in orbit as well as a station in the south pole that releases weather balloons and a ground-based spectrophotometer. This way the scientists studying the hole can know the thickness of the ozone as well as the size of the hole.