'Record-breaking' ozone hole has formed over the Arctic

A hole has opened in the ozone layer over the Arctic due to a ‘polar vortex’ causing unusually freezing temperatures in parts of the atmosphere.

The European Space Agency backed Copernicus Atmosphere Monitoring Service (CAMS) has been following the ‘unusual ozone hole’ since it first formed.

It comes as record-breaking low levels of ozone are recorded over the northern most part of the Earth at about 11 miles above the surface – the lowest levels since 2011. 

The hole over Antarctica in the southern hemisphere forms annually but a hole over the Arctic is a rare occurrence, according to ESA.

Holes do occasionally appear over the Arctic, but this is the largest discovered to date and it is due to a colder than usual ‘polar vortex’ in the stratosphere.  

These images show the ozone over the Arctic in April and March, revealing the lower than usual levels recorded by Copernicus satellites

ESA say atmospheric conditions were to blame for the new new – causing by an extremely strong polar vortex mixing with post-winter sunlight. 

The new Arctic hole is a fraction of the size of the Antarctica one and is expected to close up again by the middle of April.

‘Our forecasts suggest that temperatures have now started to increase in the polar vortex’, comments Vincent-Henri Peuch, Director of the Copernicus Atmosphere Monitoring Service. 

‘This means that ozone depletion will slow down and eventually stop, as polar air will mix with ozone-rich air from lower latitudes,’ he said. 

‘It is very important to maintain international efforts for monitoring the annual ozone hole events and the ozone layer over time.’ 

Levels of ozone over the Arctic are at a very low level – the last time it was this bad was during the Spring of 2011 and this year looks set to be worse, ESA said. 

‘While we are used to ozone holes developing over the Antarctic every year during the Austral spring, the conditions needed for such strong ozone depletion are not normally found in the Northern Hemisphere,’ the Copernicus team wrote.

The ozone hole over Antarctica is primarily caused by human-made chemicals including chlorine and bromide that migrate to the stratosphere.

This is a layer of the atmosphere around 6 to 30 miles above sea level. 

These chemicals accumulate inside the strong polar vortex that develops over the Antarctic every winter where they remain chemically inactive in the darkness. 

Temperatures in the vortex can fall to below -108 degrees Fahrenheit and polar stratospheric clouds (PSCs) can form.

These clouds play an important part in chemical reactions involving the human-made chemicals that lead to ozone depletion once sunlight returns to the area. 

‘This depletion has been causing an ozone hole to form annually over the last 35 years, but the 2019 Antarctic ozone hole was actually one of the smallest we have seen during that time,’ the team wrote.

The graph shows the ozone column over the Arctic for the past year, with comparisons per decade with the black line showing 2020 levels at a record-low rate

The Arctic stratosphere is usually less isolated than its Antarctic counterpart because the presence of nearby land masses and mountain ranges disturbs the weather patterns more than in the Southern Hemisphere. 

This explains why the polar vortex in the Northern Hemisphere is usually weaker than in the Southern Hemisphere, and temperatures do not fall so low. 

In 2020 the Arctic polar vortex has been exceptionally strong and long lived with  temperatures in the Arctic stratosphere dropping low enough for several months at the start of 2020 to allow the formation of PSCs.

‘Ozone depletion over the Arctic in 2020 has been so severe that most of the ozone in the layer between 80 and 50 hPa (an altitude of around 11 miles) has been depleted,’ the Copernicus team wrote in a blog post.

Measurements from satellites are combined with computer models of the atmosphere in a similar way to weather forecasts to monitor the ozone layer.

Monitoring the ozone hole is important as the stratospheric ozone layer acts as a shield, protecting all life on Earth from potentially harmful ultraviolet radiation.  

WHAT IS THE OZONE LAYER?

Ozone is a molecule comprised of three oxygen atoms that occurs naturally in small amounts. 

In the stratosphere, roughly seven to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress immune systems and also damage plants. 

It is produced in tropical latitudes and distributed around the globe. 

Closer to the ground, ozone can also be created by photochemical reactions between the sun and pollution from vehicle emissions and other sources, forming harmful smog.

Although warmer-than-average stratospheric weather conditions have reduced ozone depletion during the past two years, the current ozone hole area is still large compared to the 1980s, when the depletion of the ozone layer above Antarctica was first detected. 

In the stratosphere, roughly seven to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation

This is because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss. 

In the 1970s, it was recognised that chemicals called CFCs, used for example in refrigeration and aerosols, were destroying ozone in the stratosphere.  

In 1987, the Montreal Protocol was agreed, which led to the phase-out of CFCs and, recently, the first signs of recovery of the Antarctic ozone layer. 

The upper stratosphere at lower latitudes is also showing clear signs of recovery, proving the Montreal Protocol is working well.

But the new study, published in Atmospheric Chemistry and Physics, found it is likely not recovering at latitudes between 60°N and 60°S (London is at 51°N).

The cause is not certain but the researchers believe it is possible climate change is altering the pattern of atmospheric circulation – causing more ozone to be carried away from the tropics.

They say another possibility is that very short-lived substances (VSLSs), which contain chlorine and bromine, could be destroying ozone in the lower stratosphere.

VSLSs include chemicals used as solvents, paint strippers, and as degreasing agents.

One is even used in the production of an ozone-friendly replacement for CFCs.