16 September, 2019

This year celebrates over three decades of remarkable international cooperation to protect the ozone layer and the climate under the Montreal Protocol. The latest Scientific Assessment of Ozone Depletion completed in 2018, shows that, as a result, parts of the ozone layer have recovered at a rate of 1-3% per decade since 2000.

Automated measurements from Halley Research Station

Jonathan Shanklin, a member of the British Antarctic Survey research team that discovered the ‘ozone hole’, gives his interpretation of the latest observations from Halley Research Station Halley station.  The station is currently unoccupied, but an automated Dobson spectrophotometer has successfully resumed operation and is providing data.  The instrument is providing the much needed ground truth for satellite observations and continues the long series of observations that led to the discovery of the ozone hole.  Together these measurements suggest that Halley has not yet been within the 2019 ozone hole.

Jonathan was at Halley during the 2017/18 Antarctic summer and worked on the calibration of the automated Dobson.  He says

“The automated instrument is a great improvement on the manual technique – it keeps going 24 hours a day during the summer, which no human observer could do!”

The most unusual hole since 2002

The 2019 ozone hole began forming in mid August, however it is proving to be the most unusual one since 2002.  It had reached an area of 11 million square kilometres in early September, when the annual “spring warming” event kicked in much earlier than usual.  The hole may have already reached its maximum size, a little smaller in area than the Antarctic continent.  Measurements at Rothera station showed that ozone values started to drop from late July as sunlight began to illuminate the stratospheric clouds (aka ‘mother-of-pearl’ clouds) that formed over the winter.  This kicked into play photochemical reactions that are destroying ozone at about 1% a day.

This chemistry originates with chlorine from CFCs and allied chemicals as well as bromine from halons used in fire-extinguishing systems.  Release of such ozone destroying substances is restricted under the Montreal Protocol, which was first signed on September 16, 1987 – World Ozone Day.  Overall the Protocol is working well, with the amount of ozone destroying gasses in the atmosphere going down.  Due to some recent illegal manufacture and release they are not dropping quite as rapidly as predicted, and we are likely to have Antarctic ozone holes for another 50 years or more.


The Dobson spectrophotometer is named for the Oxford professor of physics who in the 1930s designed what is still a world standard instrument for measuring ozone.

The Montreal Protocol was strictly first signed between September 14 and 16.

In an unprecedented event the polar vortex (and hence the ozone hole) split into two in 2002.  It is equally unprecedented for ozone depletion to be consistently greater over the Antarctic Peninsula than over Halley or the South Pole.