Arctic warming linked to little-studied GHGs

Icebergs discharged from Greenland's Jakobshavn Glacier.

A RECENT study by researchers at Columbia University has found that ozone depleting substances (ODSs)—long-lived artificial halogen compounds, such as chlorofluorocarbons (CFCs) and hydro-chlorofluorocarbons (HCFCs), responsible for the hole in the earth’s stratospheric ozone—caused about a third of all global warming from 1955 to 2005, and half of Arctic warming and sea ice loss during that period. They thus acted as a strong supplement to carbon dioxide, the most pervasive greenhouse gas (GHG); their effects have since started to fade, as they have slowly dissolved and are also no longer produced following the Montreal Protocol of 1987.

A 1985 research paper was the first to report the ozone hole over Antarctica and that it was caused by ODSs. Although the ozone-destroying effects of these substances are now widely understood, there has been little research into their broader climate impacts prior to this study.

Ozone-depleting substances were developed in the 1920s and 1930s and were used as refrigerants, solvents and propellants. Being entirely manmade, ODSs did not exist in the atmosphere before. Atmospheric concentrations of most ODSs peaked in the late 20th century and have been declining since. However, the new study finds that for at least 50 years the climate impacts of ODSs were extensive.

Because the Arctic is losing ice at a worrying pace, the Columbia researchers wanted to understand why the area is warming much faster than other regions. The team used climate models of global climate change to understand the effects of ODSs on Arctic climate, one with ODSs and the other without, both developed at the National Centre for Atmospheric Research (NCAR) of the United States.

With ODSs factored in, Arctic temperatures rose 1.59 °C. With ODSs excluded, the warming was only half as much, by 0.82 °C. Comparatively, the model indicated that global temperatures increased 0.59 °C with ODSs and 0.39 °C without. The researchers concluded that ODS greatly exacerbated Arctic warming for half a century, though the exact mechanism for why it is affected so disproportionately is not yet understood.

The results highlight the importance of the Montreal Protocol, which has been signed by nearly 200 countries, say the authors. “Climate mitigation is in action as we speak because these substances are decreasing in the atmosphere, thanks to the Montreal Protocol,” said Lorenzo Polvani, lead author of the study. “In the coming decades, they will contribute less and less to global warming.”