To conclude that July 22 is the hottest day in human history, scientists analyzed over 100 million documents using a special technique.
On July 21, the Copernicus Climate Change Service (C3S) of the European Union confirmed that this was the hottest day ever recorded in history. Just 24 hours later, this record was quickly broken, with July 22 becoming the hottest day in human history.
Many people doubt the accuracy of these claims. Even the most knowledgeable meteorologists cannot place thermometers in every corner of the world to calculate the average temperature for the day. So what technique did they use to confidently declare July 22, 2024, as the hottest day in history?
A Global Climate Picture
Copernicus employed a “reanalysis” technique that combines temperature data with climate systems.
As a result, this center has created a near real-time temperature picture of the Earth’s climate. The data presented includes temperature, wind, rainfall, and boasts an accuracy of up to 30 km2. This data can record global temperatures from the 1940s to the present day.
A pedestrian using a handheld fan while crossing an intersection during a heatwave in Tokyo on July 4. (Photo: CFP).
In addition to the newly recorded hottest day in history, data from climate images also show that 2023 is the hottest year on record, and the last 13 months have also been the hottest.
Although it is impossible to place thermometers everywhere, Copernicus receives about 100 million weather data points daily for reanalysis. “Climate information flows to our center every day,” said Carlo Buontempo, director of the Climate Change Center under the European Centre for Medium-Range Weather Forecasts (ECMWF).
This 100 million weather data comes from aircraft, satellites, ships, radar, and ground weather stations. These include information on temperature, wind, rain, snow, and air pollution worldwide.
This data will be integrated into a system called ERA5 – which has been programmed with comprehensive information about global climate history.
A fan cooling off in the Concorde Stadium of the Paris 2024 Olympic Games on July 30. (Photo: Bloomberg).
However, this data still has certain shortcomings. Weather data collection devices may not record accurate information in overcast conditions. Therefore, scientists will use ERA5 to make weather predictions and then compare them with actual weather information from nearby areas.
In other words, a temperature forecast at a specific location will be compared with all the data that ERA5 has received. This is why this technique is referred to as “reanalysis.”
The process of making predictions and then matching them with actual data from ERA5 is repeated until no errors are recorded. In this way, scientists can create an accurate and complete picture of the world’s climate. This is how the declaration that July 22 is the hottest day in the world was made.
The Highest Temperatures in 100,000 Years
Globally, the five largest weather agencies (the National Oceanic and Atmospheric Administration and NASA in the United States, ECMWF, the China Meteorological Administration, and the Japan Meteorological Agency) all use this technique to assess temperature.
Despite differences in systems and measurements, the general conclusions regarding climate records from these agencies are almost identical. Specifically, agencies agree that recent temperatures are the highest in the last 100,000 years.
According to studies, global average temperatures typically peak in mid-July and August each year. Before July 21, the record for the hottest day in the world belonged to May 7, 2023.
However, in the context of a strengthening El Niño, most forecasting agencies believe this record will soon be “overthrown.” Therefore, the reanalysis technique is increasingly valued to ensure the most accurate global temperature forecasts possible.
A delivery driver resting in hot weather in Philadelphia on June 21. (Photo: Bloomberg).
The reanalysis technique is not only useful for making announcements of “the hottest day in history” but is also used to train AI weather forecasting models.
This technique is also employed by solar and wind energy companies to calculate total energy production and how to maximize energy generation.
Copernicus is researching a new model called ERA6 with higher accuracy, which can use reanalysis techniques to create a climate picture accurate to within 14 km2.
For Director Buontempo, claims about the hottest day in history do not contribute significantly to sustainable development efforts. Using a single day as a benchmark for climate change gives the impression that temperature changes have only occurred recently, he said.
“We need to help people understand that climate change has been ongoing for a long time and affects many areas,” he emphasized. “We must make announcements as direct and understandable as possible.”
