Even a tropical country like Bangladesh couldn’t escape the wrath of the distorted polar vortex.
During winter, more often than not, a large part of northern United States is hit by an Arctic blast, sometimes severe, sometimes less severe, that lasts for a week or two. But this winter’s blast plunged not only the Midwest and the Northeast into a deep freeze with bone chilling temperatures as low as negative 25 degrees Celsius ‒ negative 35 degrees with wind chill, it also tested the mettle of millions of people living in the Deep South ‒ from Texas to Florida to the Carolinas ‒ who seldom experience sub-freezing temperature. In the midst of the cold spell, a rapidly intensifying cyclone, known as bombogenesis or “bomb” cyclone triggered by an extreme drop in atmospheric pressure, dumped 15-25 centimetres of snow in the Northeast while winds were howling at 80-120 kilometres per hour. This was followed by another winter storm that blanketed the Upper Midwest and parts of New England in the Northeast with wind-driven snow, freezing rain and sleet.
Unsurprisingly, the unforgiving Arctic freeze and record-breaking temperatures prompted Donald Trump, the cheerleader of climate deniers, to tweet, “In the East, it could be the COLDEST New Year’s Eve on record. Perhaps we could use a little bit of that good old Global Warming that our Country, but not other countries, was going to pay TRILLIONS OF DOLLARS to protect against. Bundle up!”
Trump’s favourite news source, the conservative Fox News Channel, probably failed to alert him that while we were shivering in the sub-zero temperatures, residents of Alaska, historically the coldest state during winter, were enjoying a relatively balmy weather, with temperatures most of the times staying above the freezing mark. And for information of those dancing to the tunes of their cheerleader who is “ignorant of his own ignorance” about global warming, extreme hot days in the U.S. over the past 365 days are beating extreme cold days by three to one, notes the climate change tracking platform Climate Signals.
Leading an administration without a science adviser, Trump seems to have no awareness whatsoever that the cold snap covered barely one percent of the Earth’s surface. He was also unaware that while the United States was experiencing record-breaking low temperatures, some regions in Australia were experiencing hottest weather in nearly 80 years with temperatures in Sydney hitting as high as 47.3 degrees Celsius.
In fact, despite a frigid December, last year was one of the hottest years on record, surpassing a number of all-time global heat records. Moreover, it occurred without the warming influence of El Niño that helped boost the global temperature to record levels the previous two years. Furthermore, notwithstanding the blustery Arctic freeze, the average temperature in New York and surrounding areas so far in January is five degrees Celsius ‒ almost twice the average for this time of the year.
Clearly, Trump’s tweet tells us that he doesn’t understand the difference between weather and climate. Weather is a local phenomenon, describing what happens in a particular region on a shorter time scale, such as the Arctic blast we recently went through. Climate on the other hand refers to how the atmosphere acts over a long period of time. Simply put, climate can be thought of as the cumulative average of many variables of the atmosphere, oceans and landmasses, such as temperature, rainfall, or snowfall, or extent of snow cover, over many years. Therefore, it takes much longer than one season of bitter cold, not two or three weeks, to have any long-term effect on the climate.
Although it may sound counterintuitive, extreme cold spells in the Northern Hemisphere are caused, at least in part, by climate change, global warming in particular. How? The answer lies in the cold air mass, which under normal circumstances, sits above the poles in an area called the polar vortex. It is a large, low-pressure zone that exists at two levels of the atmosphere, one in the troposphere, where most of the weather phenomena occur, and the other a bit higher up, in the stratosphere, home of the ozone layer that protects us from the harmful effects of ultraviolet radiation. The vortex rotates counter-clockwise at the North Pole and clockwise at the South Pole. The vortices are seasonal atmospheric phenomena not necessarily created by global warming.
However, scientists believe that global warming distorts the vortex in the North Pole, thereby resulting in a sudden plunge in temperature south of the Arctic Circle. That’s because increases in global temperature are not evenly spread around the world. They are greater on land and at higher latitudes. Consequently, on average, Arctic temperatures have increased in recent decades at about twice the global average. The picture for Antarctica is less clear because the Antarctic climate has behaved differently in different regions and seasons.
As a result of warming, more ice of the Arctic Ocean is melting during the summer months. Recently declassified data from the U.S. Navy nuclear submarines operating under the polar ice along with many oceanographic studies suggest that the summertime coverage of Arctic Ocean’s ice has declined some 25 percent since 1979, with more modest but still significant declines in other seasons.
As the ice melts, the Arctic ice sheets reflect less sunlight, causing the Arctic Ocean to absorb more heat, which it then releases into the atmosphere, adding to warming. This process, and other Arctic feedback loops, are known as Arctic Amplification. Eventually, the amplification has a ripple effect extending well into the stratosphere, weakening and distorting the polar vortex, thus allowing the air to escape south. In other words, instead of staying where it belongs in winter, closer to the Arctic Circle, the air moves down south into continental United States, Europe and Asia. Hence, the extreme cold spells.
Even a tropical country like Bangladesh couldn’t escape the wrath of the distorted polar vortex. On 7 January 2018, the country recorded the lowest temperature in five decades as mercury nosedived to a chilling 2.6 degrees Celsius in Tetulia.
While climate pundits are predicting that our planet could warm, on average, roughly two degrees Celsius by the end of the century, we should not interpret that to mean an end to bitter cold waves during winter any sooner. Arctic blasts will still occur, but depending on how much greenhouse gases we dump into the atmosphere, they will become rarer over time.
Nevertheless, the message from the recent Arctic blast is loud and clear. Our romance with fossil fuels have fundamentally changed the global weather systems to the point where we have to do something drastic if we want to live on the only habitable planet in the solar system beyond the twenty-first century.
The writer, Quamrul Haider, is a Professor of Physics at Fordham University, New York