On the occasion of July 14, franceinfo invites you to visualize the evolution of world temperatures since 1789. Global warming caused by human activities clearly appears in the second half of the 20th century.
Posted
Reading time : 1 min.
:quality(50)/2023/07/12/64aec8ca37cb2_075-pitton-notitle220803-npoha.jpg)
What was the weather like on July 14, 1789, the day the Bastille was stormed? During this revolutionary period, Paris experienced a cool summer, a far cry from those we experience today under the effect of global warming caused by human activities. It was 17.8°C on average in July 1789 in the streets of the capital, compared to 23°C in 2022.
>> Is it hot or cold for the season? Compare today’s weather to temperature history
This climate change is particularly visible on the strips of global warming, a visualization developed by a British scientist. The average global temperature for each year is represented by a line. In blue, the years colder than the reference average – 1961-1990 in this case – and in red, the warmest years.
Extremely rapid warming
To reconstruct the annual temperatures of these distant centuries, climatologists rely on the first temperature readings – the thermometer was invented in the 17th century – and on a multitude of natural climatic archives: tree rings, ice cores or sediments, stalactites… “Paleoclimatologists combine all of this data to make a reliable estimate of period average temperatures”explains the climatologist Christophe Cassou, who participated in the development of this frieze for the “Journal Météo / Climat” of France Télévisions.
:quality(50)/2023/07/12/64aec933d2ca3_whatsapp-image-2023-07-12-at-16-59-17.jpeg)
The “Little Ice Age”, a period of cooling from the 15th to the 19th century, appeared clearly until 1850. This cold snap was explained by natural causes: numerous volcanic eruptions, including small particles disperse throughout the planetary atmosphere and block out sunlight, less solar activity and slowing possible ocean currents in the North Atlantic.
This cold is gradually giving way to global warming, caused by our increasing consumption during the 20th century of coal, oil and gas, fossil fuels that emit large amounts of greenhouse gases. “What is striking is the extremely rapid nature of the warming from the 1970s”, analyzes Christophe Cassou. A rhythm not seen for at least 2,000 years.