At least 49 people have died as a result of the winter storm that has been battering the United States for days. According to CBS News, these are deaths directly attributable to the wave of freezing cold — from hypothermia, road accidents, or heart attacks. In another 24 cases, the link to the extreme weather event is still being assessed. In some parts of Minnesota in particular, temperatures plummeted to -40 degrees Celsius, though much of the rest of the country also recorded figures well below zero. At the same time, snow fell across a great many states, reaching several tens of centimetres in depth — 60, for example, in Colorado. At least 800,000 people have been left without electricity.

Climate denialists seize their moment, starting with Donald Trump

What better occasion to let the trumpets of climate denialism sound? Their standard-bearer, United States president Donald Trump, immediately went on the offensive with a post published on his social network Truth in which he wrote: "Could one of the Insurrectionist Environmentalists please explain to me what happened to Global Warming?".

It is the same old climate-sceptic argument https://www.lifegate.it/spallata-trump-normative-clima-epa devoid of any scientific basis, one that conflates meteorology with climatology, yet evidently still resonates with millions of American citizens — and not only them. For this reason, it is worth dismantling it at the root, data in hand.

Meteorology and climatology are not the same thing

Let us start with definitions: meteorology describes short-term phenomena, while climatology studies trends over long and very long timescales. Even the graphic representation of the rise in average global temperature is not perfectly linear. Some years have been slightly cooler, others warmer. But the trend is clear, unmistakable, and within everyone's grasp — though evidently not that of President Trump and those who lend him credibility.

Despite the particularly extreme values of the current winter storm, cold spells in the United States are gradually becoming less frequent, shorter and less intense. Here too, this is a long-term trend that cannot be disputed in any way, provided one is acting in good faith. Between 1970 and 2021, the duration of such episodes fell by an average of six days across 97 per cent of 244 US locations examined in a study conducted by the non-governmental organisation Climate Central.

Cold spells in the United States are less frequent and less intense

Over the same reference period, moreover, the annual minimum temperature rose by an average of more than 2 degrees Celsius. Heat records also outpace cold records in the vast majority of American cities. In other words: a world afflicted by human-induced global warming does not mean the absence of cold spells, but rather their progressive thinning out.

It is also worth adding that a potential slowdown of the Gulf Stream, which keeps temperatures mild across Europe, could trigger significantly lower temperatures in the future. This is a dynamic that may seem counterintuitive, yet is once again by no means disconnected from the climate changes currently under way.

Arctic warming may contribute to slowdowns of the polar vortex

What is more, some scientists have explained that incursions of icy Arctic air can, paradoxically, be encouraged by global warming. The current storm too is the result of a distortion of the polar vortex — a semi-permanent low-pressure system present at altitude above the North Pole, which for this reason "holds" the freezing air in place. In certain cases, however, undulations occur that can "release" pockets of frozen air, which then spread towards lower latitudes.

The hypothesis put forward by experts is that the warming of the Arctic — which is occurring more rapidly than the planetary average — combined with the reduction of the ice cap, may be altering polar currents, in some situations facilitating the "spillover" southwards of Arctic air. Precisely as is happening right now in the United States.