Treaty to protect ozone layer 'saved Earth from 4.5°F global warming'

International treaty signed in 1987 to protect the ozone layer helped save our planet from 4.5°F global warming that could have resulted in a ‘scorched Earth’, study finds

  • Montreal Protocol helped save our planet from 4.5°F global warming — study 
  • International treaty, signed in 1987, led to a ban on ozone-depleting chemicals
  • Without it scientists said we would already be facing reality of ‘scorched Earth’ 
  • Treaty was signed after the discovery of a hole in ozone layer above Antarctic

Scientists say a global environmental treaty that was signed more than 30 years ago helped save our planet from 4.5°F global warming.

Without the Montreal Protocol, which was agreed in 1987 and led to a ban on ozone-depleting chemicals, researchers said we would already be facing the reality of a ‘scorched Earth’.

They painted a dramatic picture of the ‘World Avoided’ thanks to what is regarded as one of the most important international treaties in history.

It was signed after the discovery of a hole in the ozone layer above the Antarctic, the part of the upper atmosphere where ozone is found in high concentrations. 

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Influential: The Montreal Protocol, a global treaty that was signed more than 30 years ago, helped save our planet from 4.5°F global warming, scientists have said. It was agreed after the discovery of a hole in the ozone layer above the Antarctic — seen here in 2006, at its largest

In 1987, the Montreal Protocol was agreed, which led to the phase-out of chlorofluorocarbons (CFCs) and later the first signs of recovery of the ozone layer


Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. 

They are used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants.

CFCs are classified as halocarbons, a class of compounds that contain atoms of carbon and halogen atoms. 

Individual CFC molecules are labelled with a unique numbering system. 

For example, the CFC number of 11 indicates the number of atoms of carbon, hydrogen, fluorine, and chlorine.  

Whereas CFCs are safe to use in most applications and are inert in the lower atmosphere, they do undergo significant reaction in the upper atmosphere or stratosphere where they cause damage.

New modelling by an international team of scientists from the UK, USA and New Zealand revealed that if ozone-harming chemicals had been left unchecked global air temperatures would have risen by an additional 4.5°F by the end of this century. 

Banning the chemicals, which include chlorofluorocarbons (CFCs) once widely used in fridges and spray cans, protected the climate in two ways, the research found.

It helped curb their greenhouse effect and, by protecting the ozone layer, shielded plants from damaging increases in ultraviolet radiation (UV).

Ozone absorbs UV, preventing most of it from reaching the ground. 

Critically, this has protected the plants’ ability to soak up and lock in carbon dioxide from the atmosphere and thus prevented a further acceleration of climate change.  

The research team’s modelling brought together data on ozone depletion, plant damage by increased UV, the carbon cycle and climate change. 

It showed an alternative future of Earth where the use of CFCs continued to grow by three per cent a year. 

This would have led to worldwide collapse in the ozone layer by the 2040s and 60 per cent less ozone above the tropics by 2100. 

The strength of the UV from the Sun in mid-latitudes, which includes most of Europe including the UK, US and central Asia, and also New Zealand, would be stronger than the present day tropics by 2050.   

The depleted ozone layer would have seen the planet, and its vegetation, exposed to far more of the Sun’s UV.

Plants absorb carbon dioxide (CO2) through photosynthesis and studies have shown that large increases in UV can restrict plant growth, damaging their tissues and impairing their ability to undertake photosynthesis. This means the plants absorb less carbon.

Less carbon in vegetation also results in less carbon becoming locked into soils, which is what happens to a lot of plant matter after it dies. All of this would have happened on a global scale.

The researchers’ models show that in a world without the Montreal Protocol the amount of carbon absorbed by plants, trees and soils would have dramatically plummeted over this century.

With less carbon in plants and soils, more of it remains in the atmosphere as CO2.

Overall, by the end of this century without the Montreal Protocol CFC ban there would have been:

  • 580 billion tons less carbon stored in forests, other vegetation and soils;
  • An additional 165-215 parts per million of CO2 in the atmosphere, depending on the future scenario of fossil fuel emissions. Compared to today’s 420 parts per million CO2, this is an additional 40-50 per cent;
  • The huge amount of additional CO2 would also have contributed to an additional 1.4°F (0.8°C) of warming through its greenhouse effect.

Ozone depleting substances, such as CFCs, are also potent greenhouse gases and previous research has shown that their ban prevented their contribution to global warming through their greenhouse effect. 

By the end of this century, their greenhouse effect alone would have contributed an additional 3°F (1.7°C) global warming. 

This is in addition to the newly quantified 1.4°F (0.8°C) warming, coming from the extra CO2 that would have resulted from damaged vegetation, meaning that temperatures would have risen 4.5°F (2.5°C) overall.

These models show the effects on the productivity and stores of the terrestrial carbon cycle. The purple line is what is currently projected for Earth, while the orange is the ‘World Avoided’

These models show the effect of UV-driven changes in vegetation on atmospheric CO2 and surface temperature. The purple line is what is projected for Earth and the orange is what was avoided thanks to the Montreal Protocol

Dr Paul Young, lead author from Lancaster University, said: ‘Our new modelling tools have allowed us to investigate the scorched Earth that could have resulted without the Montreal Protocol’s ban on ozone depleting substances.

‘A world where these chemicals increased and continued to strip away at our protective ozone layer would have been catastrophic for human health, but also for vegetation. The increased UV would have massively stunted the ability of plants to soak up carbon from the atmosphere, meaning higher CO2 levels and more global warming.

‘With our research, we can see that the Montreal Protocol’s successes extend beyond protecting humanity from increased UV to protecting the ability of plants and trees to absorb CO2. 

‘Although we can hope that we never would have reached the catastrophic world as we simulated, it does remind us of the importance of continuing to protect the ozone layer. Entirely conceivable threats to it still exist, such as from unregulated use of CFCs.’

The planet has already seen 1.8°F (1°C) warming from pre-industrial temperatures. 

Even if we had somehow managed to get to net zero CO2 emissions, the additional 4.5°F (2.5°C) rise would take us to a rise of 6.3°F (3.5°C).  

This is far in excess of the 2.7°F (1.5°C) rise above pre-industrial levels that many scientists see as the most global temperatures can rise in order to avoid some of the most damaging effects of climate change.

Dr Chris Huntingford of the UK Centre for Ecology & Hydrology said: ‘This analysis reveals a remarkable linkage, via the carbon cycle, between the two global environmental concerns of damage to the ozone layer and global warming.’

The research has been published in the journal Nature. 

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.

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