The hole in the ozone has shrunk to its smallest size since records began due to higher antarctic temperatures finds NASA.
Discovered in 1982, the ozone hole naturally increases and then decreases in size annually and is usually at its largest during late September or early October.
However warmer temperatures globally and abnormal weather patterns in the upper atmosphere over Antarctica have seen the depletion of the ozone halt this year.
Observations by NASA and the National Oceanic and Atmospheric Administration (NOAA) found that the hole reached its peak dimensions for the year at 6.3 million square miles on September 8 and then suddenly shrunk in size to less than 3.9 million square miles.
During years with average weather the hole usually reaches a maximum size of about 8 million square miles by late September or early October.
Paul Newman, scientist for Earth Sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said: ‘It’s great news for ozone in the Southern Hemisphere.
‘But 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.’
The highly reactive ozone compound, also known as trioxygen, is comprised of three oxygen atoms and is a pale blue gas with a pungent smell and can be found 25 miles above the Earth’s surface in the stratosphere.
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 reacting with high-energy ultraviolet rays the ozone acts as a layer of sun screen absorbing them into the stratosphere.
Ozone is created primarily by ultraviolet radiation when high-energy ultraviolet rays strike ordinary oxygen molecules (O2), splitting the molecule into two single oxygen atoms, known as atomic oxygen – this freed oxygen atom then combines with another oxygen molecule to form a molecule of ozone (O3).
This reaction helps shield the planet from potentially harmful ultraviolet radiation that can cause skin cancer and 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
By early October the ozone hole can be seen to have shrunk to around 3.9 million square miles
The Antarctic ozone ‘hole’, which is technically not a hole but an area of depletion, forms during the Southern Hemisphere’s late winter (September/October) 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.
The Aura satellite’s Microwave Limb Sounder also estimates levels of ozone-destroying chlorine in the stratosphere.
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 found to be 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.’
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.
The upper stratosphere at lower latitudes is also showing clear signs of recovery, proving the Montreal Protocol is working well.
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.
A diagram showing how man-made chemical compounds such as Chlorofluorocarbons (CFCs) are released into the atmosphere and destroy the ozone