For the first time, scientists have quantified the contribution of so-called ozone-depleting substances, like chlorofluorocarbons (CFCs), to extreme Arctic warming. The important, yet oft-forgotten, group of greenhouse gases were responsible up to half of the effects of climate change in the Arctic in the second half of the twentieth century, according to the new study, published on 20 January in Nature Climate Change (1).
Arctic warning presents some of the most indisputable evidence of climate change and is thought to have been driven by huge increases in greenhouse gas emissions following the Industrial Revolution. The Arctic is warming twice as fast as the global average. The disproportionately high toll of climate change in this region, known as Arctic amplification, has long baffled scientists.
Now, a set of potent, yet often overlooked, greenhouse gases may provide the answer. Most previous studies on these chemicals focused on their ozone-depleting effects — the chemicals are responsible for the Antarctic ozone hole in the Southern Hemisphere — but they may have also played a significant role in global warming.
In fact, ozone-depleting gases can warm the atmosphere thousands of times more efficiently than carbon dioxide. To determine just how much these substances have contributed to Arctic warming, an international team of researchers — including scientists from Columbia University in the US, the Institute for Atmospheric and Climate Sciences in Switzerland, and the University of Toronto, Canada turned to well-established climate models. They quantified global warming between 1955 and 2005, both with or without ozone-depleting substances. Although the uncertainties and complexity of climate models make it difficult to precisely quantify the effects.
In particular, the authors looked at emissions of CFCs, which include propellants and refrigerants, that have been around since the 1920s and 1930s. The chemicals were later banned by the 1987 Montreal Protocol and started being phased out from 1989 onwards.
Without CFCs, the simulations showed an average Arctic warming of 0.82 °C. But when the ozone-depleting gases were added to the mix of greenhouse gases, this increased to 1.59 °C. By varying the thickness of the ozone layer, the authors were able to show that the additional warming was directly caused by the ozone-depleting chemicals and not just the effects of the depleted ozone layer.
Since atmospheric concentrations of CFCs have been on the decline since the turn of the century, the results offer some hope that Arctic warming and melting of the Arctic ice sheets could stabilise in future as concentrations continue to drop.
The authors write: “Our findings also have implications for the future because the phase-out of [ozone-depleting substances], which is well underway, will substantially mitigate Arctic warming and sea-ice melting in the coming decades,”
But, of course, this is not certain as many other factors, in particular, rising carbon dioxide emissions — which actually peaked in 2019 — contribute to global warming. Moreover, despite a global crackdown, CFCs are still used around the world. And let’s not forget that the hydrofluorocarbons introduced to replace CFCs are still more potent than carbon dioxide.
Furthermore, the already vanishing sea ice sheets could have unstoppable cascading effects. Real and immediate action is needed to reduce the emissions of all greenhouse gases to prevent the potentially devastating effects of climate change.
(1) Polvani, L.M. et al. Substantial twentieth-century Arctic warming caused by ozone-depleting substances. Nature Climate Change (2019). DOI: 10.1038/s41558-019-0677-4