The hole in the ozone layer has shrunk to its smallest size since scientists began monitoring it in 1982 because of unusual weather patterns in the upper atmosphere over Antarctica, according to NASA.
The hole fluctuates in size annually and is usually largest during the coldest months in the southern hemisphere, from late September to early October.
The latest observations from space have shown the hole now covers less than 3.9million square miles – a record low and almost half as small as it was during its peak at 6.3million on September 8 only six weeks ago. Experts say the hole is usually around 8 million square miles during this time of year.
Paul Newman, chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center said it is ‘great news for ozone in the Southern Hemisphere’.
But he warned: ‘It’s important to recognize that what we’re seeing this year is due to warmer stratospheric temperatures. It’s not a sign that atmospheric ozone is suddenly on a fast track to recovery.’
Between September and October, the hole shrunk to around 3.9 million square miles (10 million square kilometres) — the lowest size at which it has ever been recorded
Observations by NASA and NOAA found that the hole reached its peak dimensions for the year at 6.3 million square miles on September 8
By early October the ozone hole can be seen to have shrunk to around 3.9 million square miles. The Dobson Unit can be seen on the left, measuring the amount of a trace gas in a vertical column through the Earth’s atmosphere
The hole in the ozone was at its largest in September 2006, when it covered a massive 10.6million square miles
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.
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.
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.
At lower latitudes, the upper stratosphere is also showing clear signs of recovery, suggesting the Montreal Protocol is working well.
According to NASA, the ‘main ingredient’ in the ozone-destroying process is are so-called polar stratospheric clouds.
These relatively rare bodies occur high in the stratosphere at altitudes between 49,000–82,000 feet (15,000–25,000 metres) above the surface.
These clouds provide a surface on which chemical reactions can occur — releasing waste products called ‘free radicals’ which go on to destroy ozone particles around them.
Fewer polar stratospheric clouds form in warmer weather, however, and they also last for shorter periods of time in such conditions.
This year’s warmer global temperatures — aided by unusual weather patterns — have therefore helped to limit the development of these clouds and also given those did form less time to damage the ozone layer.
In turn, this has led to a much smaller ozone hole this year than we have previously seen.
On the surface, the strengthening of the ozone layer would seem to be a promising development — as such serves to better protect the Earth from harmful ultraviolet radiation from the Sun.
However, the news that the hole is shrinking is not necessarily a good sign — as the process that is closing the hole is a clear product of rising global temperatures.
In years with more typical weather, the hole usually reaches a maximum size of about 8million square miles by late September or early October — before shrinking back down again.
Gases released from man-made processes on Earth are eroding away the layer of ozone gas which surrounds the globe. Holes in the layer mean more heat from the Sun makes it through and down to Earth level, which is warming the surface and oceans
The highly reactive ozone molecule — also known as trioxygen — comprises three oxygen atoms and is a pale blue gas with a pungent smell.
It can be found 25 miles above the Earth’s surface, in the stratosphere.
By reacting with high-energy, ultraviolet rays the ozone acts like a layer of sun screen — absorbing the harmful rays in the stratosphere before they reach Earth’s surface.
Ozone is created primarily by ultraviolet radiation, when high-energy ultraviolet rays strike ordinary oxygen molecules (O2).
This splits the molecule into two single oxygen atoms — dubbed ‘atomic oxygen’ — with the freed oxygen atoms going on to combine with regular oxygen molecules to form ozone (O3).
This reaction helps shield the planet from potentially harmful ultraviolet radiation that can cause skin cancer, cataracts, suppress immune systems and also damage plants.
The ozone depletion seen in blue growing over the month of August 2019, pictured in August 7 (left) and August 27
The Antarctic ozone ‘hole’, which is technically not a hole but an area of depletion, forms during the Southern Hemisphere’s late winter as the returning Sun’s rays start ozone-depleting reactions.
These runaway reactions involve chemically active forms of chlorine and bromine derived from man-made compounds and take place on the surfaces of cloud particles in cold stratospheric layers — breaking up ozone molecules.
Warmer temperatures mean fewer polar stratospheric clouds form, limiting the ozone-depletion that can take place on their surface.
NASA and NOAA monitor the ozone hole using satellites including NASA’s Aura satellite, the NASA-NOAA Suomi National Polar-orbiting Partnership satellite and NOAA’s Joint Polar Satellite System NOAA-20 satellite.
At the South Pole, NOAA staff launch weather balloons carrying ozone-measuring ‘sondes’ which directly sample ozone levels vertically through the atmosphere.
The flight path of an ozonesonde as it rises into the atmosphere over the South Pole from the Amundsen-Scott South Pole Station. Scientists release these balloon-borne sensors to measure the thickness of the protective ozone layer high up in the atmosphere. Time-lapse photo taken Sept. 9, 2019
Most years, at least some levels of the stratosphere —the region of the upper atmosphere where the largest amounts of ozone are normally found — are completely devoid of ozone.
Bryan Johnson at NOAA’s Earth System Research Laboratory in Boulder, Colorado said: ‘This year, ozonesonde measurements at the South Pole did not show any portions of the atmosphere where ozone was completely depleted.’
While this is uncommon, it is not unprecedented. This is the third time in the last 40 years that weather systems have caused warm temperatures that limit ozone depletion, said Susan Strahan, an atmospheric scientist with Universities Space Research Association, who works at NASA Goddard.
The polar solar vortex seen in red over the south pole which was unusually ‘wonky’ this year
Similar weather patterns in the Antarctic stratosphere in September 1988 and 2002 also produced atypically small ozone holes, she said.
Dr Strahan said: ‘It’s a rare event that we’re still trying to understand. If the warming hadn’t happened, we’d likely be looking at a much more typical ozone hole.’
There is no identified connection between the occurrence of these unique patterns and changes in climate.
The weather systems that disrupted the 2019 ozone hole are typically modest in September, but this year they were unusually strong, dramatically warming the Antarctic’s stratosphere during the pivotal time for ozone destruction.
At an altitude of about 12 miles (20 kilometers), temperatures during September were 29F (16˚C) warmer than average, the warmest in the 40-year historical record for September by a wide margin.
In addition, these weather systems also weakened the Antarctic polar vortex, knocking it off its normal center over the South Pole and reducing the strong September jet stream around Antarctica from a mean speed of 161 miles per hour to a speed of 67 miles per hour.
This slowing vortex rotation allowed air to sink in the lower stratosphere where ozone depletion occurs, meaning the Antarctic lower stratosphere was warmed – limiting polar stratospheric clouds where the ozone destroying reactions take place.
The strong weather systems also brought ozone-rich air from higher latitudes elsewhere in the Southern Hemisphere to the area above the Antarctic ozone hole.
A combination of these two effects led to much higher than normal ozone levels over Antarctica compared to ozone hole conditions usually present since the mid 1980s.
As of October 16, the ozone hole above Antarctica remained small but stable and is expected to gradually dissipate in the coming weeks.