• Amalia Heide


"In the East, this could be the coldest New Year's Eve on record. Perhaps we could use some of that good old global warming that our country, but no other countries, was going to pay trillions of dollars to protect against. Bundle up," tweeted the former US president a few years ago, confusing climate with weather."

Tweet made by Donald Trump on 29/12/2017

Misinformation is very present in our societies today. The speed with which social networks such as Facebook or Twitter manage to circulate false information is worrying. Donald Trump's presidential term has had as a fundamental pillar to misinform American citizens in different areas of life by using the media. The scientific field could not escape this wave of fake news. Indeed, Donald Trump's refusal to take action to mitigate the impact of climate change has led him to deny the existence of this phenomenon, mixing and confusing concepts such as climatology and meteorology to justify his actions. The main purpose of this article is to understand the difference between weather and climate in order to avoid the widespread unawareness of such an alarming phenomenon as climate change.

Meteorology is the scientific study of instantaneous and local atmospheric or meteorological phenomena. The quantities studied are temperature, atmospheric pressure, wind, humidity, rainfall and cloud cover. Meteorology allows the short-term (days, weeks) forecasting of a variety of climatic phenomena such as droughts, storms or floods and is used to protect populations from natural disasters.

Statistical procedures make it possible to deduce the evolution of the weather over time from all this meteorological data, which is known as climatology. The quantities used in climatology are the same as those used in meteorology but require observation over the medium to long term (years, decades, millennia etc.). The study of the earth's global climate is based mainly on variations in the global average temperature.

Illustration of the difference between weather and climate

The recurrent confusion between the notions of climate and weather leads people to draw conclusions about the evolution of the planet's temperature by assuming that if one has experienced an extremely cold winter it is incomprehensible to stop thinking about the phenomenon of global warming, which one associates with heat. This is the thought that Donald Trump sought to propagate when on 29 December 2017 in New York the minimum temperature was -9°C/-5°C, denying the existence of global warming and mocking, via Twitter, those who are aware of its existence. However, it is necessary to contradict this idea, which has no scientific basis, and to recall that a very harsh winter in a specific geographical location (in this case New York) does not mean that in another part of the world a heat wave cannot occur. This was the case in France during the summer of 2019 where, during the month of June, a heat wave of exceptional intensity settled over almost the entire country. While, according to climatology, the average temperature of the country in June is a minimum of 16°C and a maximum of 28°C, the temperature measured in real time by meteorology was well above average between 21 and 30 June.

Minimum and maximum temperatures expected in France on 27 June 2019 by France TV (weather study)

If we experience a heat wave in France or a cold wave in the United States, we are witnessing the measurement of an atmospheric quantity in real time and not a long-term evolution of the quantity, and consequently these temporary waves of extreme temperatures are not sufficient on their own to affirm whether the global average temperature, established by climatology, is increasing or decreasing.

Moreover, weather is measured locally and instantaneously, whereas climate takes into account the evolution on a global scale. Indeed, despite the cold snap in the United States or the heat wave in France, as temperatures vary from region to region, it is necessary to take into account all the temperatures on the earth's surface to assess how the global average temperature is evolving by carrying out statistical procedures.

Global climates and average annual temperature by parallel

For this reason, the study of the earth's global climate is calculated from measurements at different points on the globe at the level of continents and oceans. For example, the average temperature at the poles is characteristic of cold climates, whereas the average temperature in Africa is characteristic of warm climates. In order to determine the evolution of the global average temperature, it is therefore necessary to know the average temperature of ALL climate zones in order to make statistical averages. One or two regions are not enough. If the average temperature of one or more climate zones changes, there will be a change in the global average temperature and therefore a change in climate, which can be either warming or cooling.

With this ironic tweet, which mixes concepts such as meteorology and climatology, Donald Trump misinforms his audience about the calculation of the dangerously rising global average temperature and thus postpones a pressing international problem that, according to scientists, requires immediate action.

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