The news over the past few days has been filled with repeated announcements of new global daily heat records. Thus, Tuesday, July 4 was the hottest day in history, at least since the weather data is recorded.
They are done so thanks to tools that make it possible to obtain preliminary data. However, if these can deliver a first warning of an episode of extreme heat, they must be considered with caution, underline the experts of the climate.
The University of Maine, in the United States, has set up a website, called Climate Reanalyzer, which makes it possible to visualize the curve of the average temperature at the global level, for each day of the year since 1979. Thus, we finds that on Monday, July 3, this curve reached, at its highest, 17.01°C. The next day, Tuesday July 4, it rose to 17.18°C, and on Thursday July 6 to 17.23°C.
The European climate change observatory Copernicus, which has a similar tool, confirmed the records on Monday, then on Tuesday, although there were slightly lower values.
These estimates are produced by so-called “reanalysis” tools, which combine observed temperature measurements (by weather stations, satellites, etc.) and their interpretation by a computer model.
The models used explain the differences in the values ??obtained. The University of Maine relies on public data from the United States Agency for Oceanic and Atmospheric Observation (NOAA). The agency, which acknowledged that many temperature records were currently being recorded locally around the world, however distanced itself from the university’s results, saying it could not “validate the methodology or the conclusions” and prefer to focus on monthly and annual records.
The fact that Copernicus delivered similar results, however, shows that the published data can “be taken seriously,” UC Berkeley climatologist Zeke Hausfather told AFP. The European tool (named ERA5) is considered by scientists to be “the most reliable”, he said.
These are estimates that are “not official records,” Climate Reanalyzer developer Sean Birkel told AFP. “The focus should be on annual and monthly records,” which are carefully checked, added this researcher at the University of Maine. Such validations are not possible for near real-time data, due to lack of time.
On Thursday July 6, Copernicus released its analysis for June 2023 separately, announcing that it was the hottest June on record. A similar monthly analysis from NOAA is expected next week.
These reports are based “only on field observations”, which are also “far more numerous” than those injected into the reanalysis tools, explained Zeke Hausfather. As a general rule, climate experts prefer to focus on long-term trends and changes in order to eliminate variations simply related to weather.
In addition, the global average temperature is an “abstract” data that is not necessarily meaningful to the general public, notes Zeke Hausfather. “Nobody lives at the world average. »
Nevertheless, these daily data “can make it possible to begin to identify extreme events” which could “have a significance from the point of view of the climate”, judge Sean Birkel. The preliminary records detected can then be cross-checked using other databases and allow the examination of the causes of this rise in temperatures to be launched, he underlined.
“These tentative records are further evidence of shifts in global weather patterns, driven by climate change and the ongoing El Niño episode,” Omar Baddour of the World Meteorological Organization said in a statement. They are “the sign that we are heading towards a very warm period on the surface of the globe,” added Zeke Hausfather. At this rate, it looks increasingly likely that 2023 will become the hottest year since records were first recorded in 1880.”
