More than half of 20th century Arctic warming linked to ozone-depleting chemicals: Study

Ozone-depleting substances -- widely used as propellants, refrigerants, and chemical solvents during the 20th century -- may be responsible for nearly half of warming in the Arctic region between 1955 and 2005, a new study says. These chemicals, which are compounds made of halogen elements like chlorine, bromine, and fluorine, destroy the protective layer of ozone in the upper atmosphere, according to the study, published in the journal Nature.

The researchers, including Lorenzo Polvani from Columbia University in the US, said emissions of these chemicals have been curbed, with the ozone layer now slow recovering since the 1987 Montreal Protocol -- a global agreement to phase out the ozone-depleting substances. However, they said these potent greenhouse gases (GHGs) have long atmospheric lifetimes, adding substantially to human induced global warming.

"While the dominant role of carbon dioxide is undisputed, another important set of anthropogenic GHGs was also being emitted over the second half of the twentieth century: ozone-depleting substances (ODSs)," the researchers wrote in the study. Polvani and his team used a climate model to evaluate the amount of global warming that can be caused by these substances.

They ran two simulations -- one in which the natural and human emissions were measured during 1955–2005, and the other with the halogen chemicals and their ozone impacts removed. Comparing the two simulations, the scientists found the net impact of these chemicals on the climate system.

They said the impact of ODS on the Arctic was primarily not caused by ozone depletion, but by their own ability to trap the sun's radiation -- similar to other GHGs like carbon dioxide. "We also demonstrate that the large impact of ODS on the Arctic occurs primarily via direct radiative warming, not via ozone depletion," the scientists reported in the study.

According to the researchers, the ODSs may have caused about half of Arctic warming and sea ice loss, and an additional one third of globally averaged warming during the second half the 20th century. The findings, the researchers said, offer a new perspective on the climate impacts of ODSs.

They added that the continued phase-out of these chemicals via the Montreal Protocol may help mitigate further Arctic warming and sea ice melt.

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