Ozone may be heating the planet more than scientists realise

Ozone may be weakening one of Earth’s most important cooling mechanisms and heating our planet even more than we realise, a new study warns. 

An international team of researchers discovered changes in ozone levels in two layers of Earth’s atmosphere. 

In the troposphere (the lowest layer of Earth’s atmosphere), ozone has increased, which is bad news because it acts as greenhouse gas, trapping outgoing longwave radiation, and thereby heating the Earth. 

Meanwhile, ozone levels in the stratosphere (the next layer up from the troposphere) have decreased, which is also bad news, according to the team. 

Both of these changes have weakened a natural cooling mechanism of the Southern Ocean, and in turn contributed to warming of the planet.  

False-colour view of total ozone over the Antarctic pole, March 28. The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone

The Southern Ocean contributes to ocean circulation, transporting heat from the equator to the poles, causing the planet to cool overall. 

‘The ocean absorbs excess heat from Earth’s system, acting to balance the excess heat from rising global temperatures,’ study author Dr Michaela Hegglin, an associate professor at the University of Reading, told MailOnline. 

‘As the Earth’s surface warms up due to increasing greenhouse gases, water in the ocean soaks up energy (heat) and distributes it more evenly across the planet.’

Ozone (O3) – which causes a smoggy haze that can damage the lungs – is a molecule comprised of three oxygen atoms that occurs naturally in small amounts. 

It is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC), found in exhaust fumes, in the presence of sunlight. 

It’s already well known that at ground level, ozone can cause health problems for vulnerable people who suffer from lung diseases such as asthma. 

However, further up in the Earth’s atmosphere – in the stratosphere, between 31 miles and 52 miles above the ground – ozone is beneficial to us. 

In the stratosphere is the ozone layer, a thin region that absorbs almost all of the sun’s harmful ultraviolet light. 

Smog is primarily made up of ground level ozone combined with other gases and particle pollution. Picture, smog over New York 

Without the ozone layer, there would be severe increases of solar UV radiation, would would damage our DNA and make skin cancer more common. 

For the study, the team used models to simulate changes in ozone levels in the upper and lower atmosphere between 1955 and 2000, to isolate them from other influences and increase understanding of their impact on the Southern Ocean heat uptake.

These simulations showed that a decrease in ozone in the upper atmosphere and increase in the lower atmosphere both contributed to warming seen in the upper 1.2 miles (2km) of the ocean waters in the high latitudes. 

The increased ozone in the lower atmosphere caused 60 per cent of the overall ozone-induced warming seen in the Southern Ocean over the period (1955 to 2000) – far more than previously thought. 

Changes to ozone levels in the upper and lower atmosphere were responsible for 30 per cent of the warming seen in ocean waters bordering Antarctica in the second half of the 20th century, the researchers found.

Ozone hit the headlines in the 1980s when a hole was discovered in the ozone layer high in the atmosphere over the South Pole, due to damage caused by chlorofluorocarbons (CFCs), a gas used in industry and consumer products. 

This discovery of the ozone hole led to the Montreal Protocol, an international agreement to halt the production of CFCs.

‘We have known for a while that ozone depletion high in the atmosphere has affected surface climate in the Southern Hemisphere,’ said Dr Hegglin. 

Ozone hit the headlines in the 1980s when a hole was discovered in the ozone layer high in the atmosphere over the South Pole, due to damage caused by chlorofluorocarbons (CFCs), a gas used in industry and consumer products. Pictured: a map of the ozone hole over Antarctica as seen on September 16, 2020

‘Our research has shown that ozone increases in the lower atmosphere due to air pollution, which occurs primarily in the Northern Hemisphere and ‘leaks’ into the Southern Hemisphere, is a serious problem as well.

‘There is hope to find solutions, and the success of the Montreal Protocol at cutting CFC use shows that international action is possible to prevent damage to the planet.’

The stud, which is also mauthpored byu  has been published today in the journal Nature Climate Change. 

The Ozone layer sits in the stratosphere 25 miles above the Earth’s surface and acts like a natural sunscreen

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.