Damage to the ozone layer may have been responsible for half of Arctic warming over the span of 50 years, a new study claims.
An international team of researchers say the findings highlight ozone-depleting substances (ODS) as an unrecognised source of 20th century Arctic climate change.
ODS, a group of very potent greenhouse gases, are halogen compounds that destroy the protective layer of ozone in the upper atmosphere.
They may be responsible for 50 per cent of Arctic warming and sea ice loss from 1955 to 2005 and nearly one third of global average warming during that period.
‘These compounds, in addition to causing the ozone hole over Antarctica, have long been recognised at powerful greenhouse gases,’ the researchers write in Nature Climate Change.
‘While much less abundant that carbon dioxide, ODS are much more powerful greenhouse gases on a molecule-by-molecule basis.’
ODS were developed in the 1920s and 1930s and used as propellants, refrigerants and solvents during the 20th century.
They were being emitted into the atmosphere in substantial quantities in the late 1950s in particular.
But the discovery of the ozone hole of Antarctica, which causes unique atmospheric and chemical conditions there at certain times of the year, led to the phase-out of the production.
Since the Montreal Protocol, an agreement to protect the stratospheric ozone layer in 1987, ODS emissions have been curbed and the ozone layer is now in slow recovery.
However, ODS are potent greenhouse gases and have long atmospheric lifetimes, so they can add substantially to the anthropogenic greenhouse effect.
Corresponding author of the study Lorenzo Polvani and his colleagues at Columbia University in New York used a climate model to estimate what amount of climate warming can be attributed to ODS.
The team simulated two worlds – one with natural and human emissions as measured between 1955 and 2005, and another with ODCs and their ozone impacts removed – to measure net impact of ODSs on the climate.
Their models showed that when ODS numbers are kept fixed, forced Arctic surface warming and forced sea-ice loss are only half as large as when ODS are allowed to increase.
The results suggest that continued phase-out of ODS will help mitigate Arctic warming and sea ice melt in the future.
‘If our findings are confirmed by future studies, the role of the Montreal Protocol as a major environmental treaty will assume a new dimension,’ the researchers state.
ODS include chlorofluorocarbons, hydrochlorofluorocarbons and haloalkanes.
ODS are generally very stable in the troposphere – Earth’s lowest atmospheric layer –and only degrade under intense ultraviolet light in the stratosphere – the second major layer of Earth’s atmosphere.
Once in the stratosphere, they release halogen atoms through photodissociation which catalyse the breakdown of ozone (O3) into oxygen (O2).
This depletes the Earth’s protective ozone layer, leaving humans exposed to the sun’s harmful radiation.