Amid global warming, why are we in a deep freeze?

During winter, more often than not, a large part of northern United States is pummelled 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 45 degrees Celsius, it also tested the mettle of millions of people living in the Deep South, particularly Texas, a state that seldom experience sub-freezing temperature.

An onslaught of wicked wintry weather—a cocktail of heavy snow, sleet and damaging ice storm—with sub-zero temperatures knocked millions of Texans off the power grid and plunged them into deep freeze, the lowest being negative 12 degrees in Houston. Frozen and burst water pipes in homes and businesses were widespread. Unlike northern states, Texas is not equipped to handle ice, sleet or snow. As a consequence, hundreds of vehicles, including dozens of 18-wheeler, were involved in horrific and sometimes fatal pileups on untreated icy roads.

The recent extreme weather is not limited to the United States. That is because when the winter is extreme in one part of the hemisphere, it is often extreme all across the hemisphere. Thus, the "beast" from the Arctic hit Europe too. In January, Spain experienced a deadly snow storm with dangerously low temperatures. Even a tropical country like Bangladesh, especially the northern region, could not escape the wrath of the cold wave.

Snow fell hard in Greece and Turkey, where it is far less normal. Snow also fell in Jerusalem and parts of Jordan and Syria, while snow-covered camels in Saudi Arabia made for a rare sight. We also had more than our fair share of snow. In the lower Hudson Valley of New York, where I live, Mother Nature already dumped around 36 inches of snow since the last week of January, with more in the forecast. Most of the snow—24 inches—fell in a single storm event from January 31 through February 2.

Climate change deniers have often used cold winter weather to advance their argument that global warming is a Chinese hoax. In one infamous example, when an Arctic freeze descended on the northeast, including New York City, in December 2017, former US President Donald Trump tweeted, "Perhaps we could use a little bit of that good old Global Warming to protect against" harsh winters. Only someone who is "ignorant of his own ignorance" could make such a stupid statement!

It may be counterintuitive, but paradoxically, among the many factors, anthropogenic climate change is mainly responsible for the short-lived bursts of extreme winter weather that we have been witnessing in recent years. Indeed, there is strong scientific evidence that rapid heating of the Arctic caused by global warming is pushing frigid air from the North Pole further down south due to distortion of the polar vortex.

Under normal conditions, cold air is concentrated in a huge low-pressure gyre around the North Pole in an area called the polar vortex—about 15 to 50 kilometres above the Earth's surface in the layer of the atmosphere known as the stratosphere. When the vortex is strong, the jet stream—a narrow band of strong, fast-flowing wind in the upper atmosphere that generally blows from west to east all across the globe—acts as a barrier between the spinning cold air in the north and the warmer air to the south. As a result, cold air remains trapped in the Arctic, making winters in the northern mid-latitudes milder.

How does global warming distort the polar vortex? It is well-known that the rise in global temperature is not evenly spread around the world. Because of the loss of Arctic ice which otherwise would have reflected a substantial amount of solar radiation back into outer space, average temperature in and around the North Pole is increasing about twice as fast as in the mid-latitudes. This is known as Arctic Amplification. Several studies show that the amplification is particularly strong in winter. Consequently, a rapidly warming Arctic weakens the jet stream, which in turn weakens the polar vortex to the extent that it becomes distorted, thereby spilling its cold air southward.

According to meteorologists, in a span of two weeks from December to January, Arctic Amplification gave rise to a phenomenon called Sudden Stratospheric Warming, in which temperatures in the atmosphere 15 to 30 kilometres above the Arctic jumped by nearly 55 degrees, from negative 80 to negative 25 degrees. This accelerated warming weakened the jet stream considerably and subsequently distorted the vortex so severely that it got knocked off the pole, resulting in a sudden plunge in temperature south of the Arctic Circle all the way to the US-Mexico border. Hence, the once-in-a-lifetime cold winter in Texas and other southern states.

Continued rise in global temperature will not necessarily mean an end to bitter cold waves during winter any sooner. One group of researchers believe that Arctic blasts will still occur, but their intensity will depend on how much greenhouse gases we vent into the atmosphere. It is very probable that they will become rarer over time, but the ones we are experiencing now will more likely persist and last longer. Another group says that warming in the Arctic will increase the chances of frigid polar air spilling further south, leading to more periods of extreme cold days in the future, much colder than the ones we are experiencing now.

Nevertheless, the recent weather pattern clearly demonstrates that both extreme heat and extreme cold can happen side by side. Besides, two to four weeks of cold snaps do not make a winter. They are short-term weather events, while climate is about long-term trends. Arctic blasts are, therefore, not enough to compensate for the overall warming of the climate across the planet. In fact, last year was one of the hottest years on record, with the average temperature surpassing a number of all-time highs. And it occurred without the warming influence of El Niño.

Finally, we are in a deep freeze amid global warming because our "senseless and suicidal" romance with fossil fuels has fundamentally changed the global weather systems for worse.

Quamrul Haider is a Professor of Physics at Fordham University, New York.