“Day After Tomorrow” scenario in the US: Does this mean Global Warming is a hoax?

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In the last days of 2017, when much of the Eastern and Midwest US states were in the grip of a cold snap which eventually led to a “winter hurricane” known to meteorologists as a “bomb cyclone”, President Trump didn’t miss an opportunity to mock the science of global warming.

Trump, we all know that, has a rather distorted idea of what climate change is all about: However, since his words may be misleading for a lot of people, it may be about time for a short recap of a few basic concepts.

First of all, the term global warming refers to the rise in the average temperature of the whole Earth’s climate system since the start of the Industrial Revolution. Secondly, when scientists document a temperature increase, their results are based on the analysis of thousands of temperature measurements performed all over the Earth over a time span of decades.

Talking about climate, we can say that the world’s average global temperature has risen 1.5°C since 1770; on the other hand, talking about weather, we know that, on the same day of the year, it can be very cold in one part of the world and warmer than usual in another place.

Climate change analyses focus on the global average over long periods: It is bad science to argue against the reality of climate change based on observing weather conditions in a single area and on any given day of the year.

As regards the cold snap that Trump referred to as a proof of the “climate hoax”, it is easy to understand how scientifically unfounded the US President’s words are: The NASA image below shows very clearly that, while the US was struck by a “Day After Tomorrow” cold snap (blue color in the map), land temperatures were above average in the Southwest and exteme Northwest of the Country (red color in the map).


As incredible as it may seem, in December 2017, California was devastated by a series of devastating wildfires that forced about 230,000 people to flee their homes; at the same time, Alaskans witnessed the mildest winter conditions ever recorded in what is the northernmost – and normally one of the coldest – state of the US.

Moreover, as we can see from the same NASA image, at the worldwide level, during the Day After Tomorrow week in the US, temperatures were much milder all over Europe and Asia (red color); in fact, most of the Earth’s regions were warmer than average.

As Al Gore recently pointed out, during a public debate in Palm Springs, following the screening of his documentary “An Inconvenient Sequel”, a new US President is needed. America must double on its efforts to invest in wind and solar power, just like China and India have been doing with increasing success. The fight to climate change cannot be won without the fully-fledged commitment of the United States of America.

Federico Pasquaré Mariotto (Associate Professor, University of Insubria)    Fabio Luca Bonali (Post-doc researcher, University of Milan-Bicocca)