According to data from the U.S.-based National Centers for Environmental Information (NOAA), 2022 was the sixth warmest year since 1800 – that is, since we have had data on global temperatures. But, most significantly, the past nine years have been the warmest on record overall. Why then do we continue to observe extreme cold events such as frost waves? We ask this question especially during the winter. Let's clarify. Global warming explained with physics To explain the meaning of global warming, let’s start with a simple classical physics problem. If you drive your car on the highway for a distance of 100 km at a constant speed of 100 km/h, it will take you 60 minutes. If, on the other hand, you drive the same route for 60 km at 120 km/h and for the last 40 km at 90 km/h, you will take less than 57 minutes. It is true that for a certain stretch your speed was very low, but on average your speed was above 100 km/h and therefore your travel time was reduced. The same reasoning applies to the temperature of the Earth's atmosphere. Global warming is that climate phenomenon which, since the end of the 19th century, records a global increase in the average temperature on Earth. The word "average" is very important because it means that global warming does not affect all areas of the Planet equally. Some areas are warming a lot, some less, and some may even experience a decrease in temperatures. But what does matter, and this is the point that scientists all agree on, is that globally the average temperature recorded each year is increasing, to the tune of almost one degree centigrade over the last century. That global warming is taking place is confirmed by the United Nations Intergovernmental Panel on Climate Change (IPCC) in its latest report, which states, "It is virtually certain that there has been [...] a reduction in the number of cold days and nights globally since 1950. Both cold and warm extremes show a rise in temperatures." But then, what are the frost waves due to? The polar vortex hypothesis There is no doubt about it: extreme cold weather events continue to occur. The latest example is the winter storm that swept across much of the United States during Christmas 2022, with temperatures reaching minus 50 degrees Celsius, high winds, and heavy snowfall. The scientific community attributes these sudden and intense waves of cold to ripples in the polar vortex, a current of cold air that generally rotates stably over the Earth's poles. It may happen that these eddies begin to undulate, bringing cold air even to mid-latitudes and thus causing the frost waves. Again, however, the IPCC tells us that there is no scientific evidence linking climate change to an increase in polar vortex ripples. On the contrary, all the evidence indicates that the decrease in global cold extremes is also affecting the mid-latitudes. So, in conclusion, while it is scientifically proven that episodes such as the Christmas 2022 winter storm are related to polar vortex ripples, we must consider that such events are to be regarded as exceptional episodes occurring within a rapidly warming global climate context.
