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Is the ozone hole really healing?

Dr David Whitehouse, Science Editor

Claims by a UN-backed panel of experts that the ozone layer is healing and on track to full recovery may be premature and over-optimistic, Net Zero Watch’s science editor, Dr David Whitehouse, has warned.

Any internet search will find hundreds of news stories announcing that the ozone hole over the Antarctic is slowing filling and that by about the middle of this century mankind’s vandalism of this natural atmospheric layer will have been remedied. The ozone hole has become an icon of anthropogenic interference in the natural world — and a hopeful signpost that there is a way back. But is the ozone hole really healing? Not by as much as many headlines suggest, it would appear.

The ozone layer — the portion of the stratosphere that protects our planet from the Sun’s ultraviolet rays — thins to form an “ozone hole” above the South Pole every September. Chlorine and bromine in the atmosphere, derived from human-produced compounds, attach to crystals in high-altitude polar clouds initiate ozone-destroying reactions as the Sun reappears at the end of Antarctica’s winter.

Unusual behaviour for three consecutive years

The Antarctic ozone hole usually starts opening during the Southern Hemisphere spring (in late September) and begins to develop during October, usually ending during November. But this has not been the case in the past few years. Data from the last three years show a different behaviour: during this time, the ozone hole has remained larger than usual throughout November and has only come to an end well into December.

The 2022 Antarctic ozone hole was again relatively large and its closure took longer than usual, like 2020 and 2021. This is a different behaviour from what had been seen in the previous 40 years. No one is quite sure what is happening.

Speculating on the cause of this new behaviour Copernicus Atmosphere Monitoring Service Director, Vincent-Henri Peuch said:

There are several factors influencing the extent and duration of the ozone hole each year, particularly the strength of the Polar vortex and the temperatures in the stratosphere. The last three years have been marked by strong vortices and low temperatures, which has led to consecutive large and long-lasting ozone hole episodes. There is a possible connection with climate change, which tends to cool the stratosphere. It is quite unexpected though to see three unusual ozone holes in a row. It is certainly something to look into further.”

Despite these recent large ozone holes many scientists point to the consistent signs of improvement in the ozone layer. They have linked this to the success of the Montreal Protocol which, since the 1990s, has led to slow but steadily declining emissions of ozone distorting chemicals.

Over time, steady progress is being made, and the hole is getting smaller,” said Paul Newman, chief scientist for Earth sciences at NASA’s Goddard Space Flight Center. “We see some wavering as weather changes and other factors make the numbers wiggle slightly from day to day and week to week. But overall, we see it decreasing through the past two decades.”

Is the ozone hole really recovering?

Figure 1 shows the maximum size of the ozone hole. It shows signs of decline in size since 1999, but is it all that persuasive? Surely we need quite a few more years to be sure. Data: Nasa Ozone Watch.

Figure 2 shows the total ozone levels between 60° S and 60° N showing a decline until the mid-1990s and fairly constant levels since then, with a slight indication of an increase – though even that depends upon where you start estimating a trend. Figure 3b shows the equatorial region, 20° S and 20° N showing no change between 1980 -2022.

Figure 3a also shows 35° N – 60° N and figure 3c 60° S – 35° S, showing a similar behaviour though at different levels for the Northern and Southern Hemisphere. Data here.

In a 2018 study published in Atmospheric Chemistry and Physics, researchers revealed that the ozone layer is not recovering between about 60°S and 60°N. Co-author Joanna Haigh, then from Imperial College London, said that,

The potential for harm in lower latitudes may actually be worse than at the poles. The decreases in ozone are less than we saw at the poles before the Montreal Protocol was enacted, but UV radiation is more intense in these regions and more people live there.”

A recent UN report (January 2023) showed that 99% of ozone-destroying chemicals have been phased out, so why hasn’t the ozone recovery been stronger? It might be due to the long resident time ozone-destroying chemicals have in the atmosphere (about 100 years). But if that is the case, is that consistent with the very rapid onset of the ozone hole in the late 1970s? In addition climate change may be altering the way air moves in the atmosphere, slowing the recovery.

Looking at the empirical evidence it would appear that many people are looking at the recovery of the ozone layer through too hopeful an eye.