Every year, the ozone hole over Antarctica reaches an annual maximum extent during southern winter. The depletion of ozone by chlorofluorocarbons (CFCs) happens faster at colder temperatures and slows down as temperatures warm, so each October, the ozone layer begins to heal again for the year.
Scientists from NASA and NOAA work together to track the ozone layer throughout the year and determine when the hole reaches its annual maximum extent. This year, the South Pole region of Antarctica was slightly colder than the previous few years, so the ozone hole grew larger. However, scientists from NASA have developed models to predict what the ozone layer would have looked like without the Montreal Protocol, which banned the release of CFCs. Although the 2018 hole was slightly larger than that of 2017 or 2016, it was still much smaller than it would have been without the Montreal Protocol.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 184.108.40.206.0