Global warming may be to blame
SPARE A THOUGHT for the zebras in Chicago’s zoo. The creatures looked ill-equipped while clomping through the snow in sub-zero temperatures this month. The Windy City is enduring exceptionally cold weather. Forecasts suggest -31°C (-24°F) is likely on January 30th. Given the strong breezes whipping off a part-frozen Lake Michigan, that could feel more like -48°C. Schools and some offices have closed. The last time it was so frosty was a generation ago, and records could even be broken. The situation is similar across the Midwest. Universities have cancelled classes. Residents in many towns and cities have been warned to stay inside, or risk the rapid onset of frostbite. Wisconsin has declared a state of emergency, in part because of heavy snow. Although chilly winters are nothing new, the freeze this year looks unusually severe. The cause is changing air currents. But what explains them, why do they make the region so cold, and how should people cope?
Two sets of air currents determine which parts of North America and Europe get blasted by Arctic air each winter. The stratospheric polar vortex is a smallish patch of low-pressure air that circulates, anti-clockwise, in a ring some 48km (30 miles) above the Arctic. It helps to trap the coldest air near the pole and forms only in winter. A second current, the polar jet stream, flows all year round, at an altitude of about 11km, and covers a much larger area. It is affected both by the temperatures and air pressure in different parts of the globe, and by the spinning of the Earth. When the Arctic is cold and lower latitudes are reliably warm, the jet stream is more stable. The problem for America’s Midwest is that the Arctic has warmed unusually fast, a result of more greenhouse gases in the atmosphere, and so the polar jet stream is fluctuating more widely. As a result, the stratospheric polar vortex may slow down, and colder air is drawn southwards. A similar sort of shift in the air currents helped to cause the “Beast from the East” that chilled western Europe in 2018.
Is man-made climate change therefore the cause of disruption to the polar vortex? It is not yet proven beyond dispute, but some climate scientists see evidence building up. For example, Jiankai Zhang at Cambridge University and colleagues have argued in Nature Climate Change, a journal, that the loss of ice in the Barents-Kara seas, combined with increased snowfall in Eurasia, contributed to the slowdown of the Arctic polar vortex over the past three decades—and thus colder spells farther south. They warned that the “persistent sea-ice loss in the future and its associated climatic impact” are not sufficiently understood, but could suggest more changes are coming. The fact that polar sea-ice is melting faster than many climate scientists had previously expected (because of climate change) could suggest the dramatic cold spells suffered by Chicago and other cities this week will become more common.
How do residents cope? For most, the extreme cold is a temporary inconvenience. It gives them a common topic of conversation and causes some annoyances—higher heating bills, cancelled flights, closed schools and more perilous roads. Restaurants and taxis typically lose business, but services that deliver takeaway food get a boost. For the elderly and for poorer and homeless residents the consequences are far more severe. The city of Chicago provides warm shelters, though newspapers have already reported some individuals’ deaths from hypothermia. In the long run, a wider change is possible. More extreme winters could hasten the steady decline in the populations of both Chicago and Illinois, as the young head to cities on the coasts, while older residents turn their eyes to retirement in sunny Florida. Pity the zebras, then. It’s rather harder for them to move on.