Number of heat wave days seriously underestimated, study finds

Knowing the number of hot days is particularly important on a planet that, like ours, is warming. However, researchers today reveal an error in the established calculation method. An error that leads to a systematic underestimation of the frequency of days in which temperatures rise beyond normal.

Our climate is warming. In general and on average. But scientists also tell us that extreme weather events will become more frequent and intense. Precipitation, cyclones or even droughts. Perhaps most surprising is also the extremely cold weather. But, of course, also heat waves or other waveswaves of heatheat. The latter are recognized within the community of climatologistsclimatologistsbe one of those of the consequences of global warmingglobal warming the most dangerous for humanity. However, the scientists could well have been wrong in their calculations in subjectsubject.

Did you know? Global warming was first highlighted in… 1856! Discover the story of the woman who proved it in Science Hunters. © Futura

Researchers at the University of Vienna (Austria) appear to have discovered an error in the established method for searching for extreme temperatures on a planetary scale. With the result, they announce it in the magazine Nature Communicationsa systematic underestimation of the frequency of hot days.

A miscalculation that hides hot days

To understand this, you have to know that extreme temperatures are generally defined in relation to local conditions and then extended to unusually warm periods around the world. A way to compare the situation in Europe, for example, with that ofAntarcticAntarctic. Regions with very different climates.

When calculating a local temperature threshold value, windowswindows temporary call mobilemobile are often used. These windows aim to increase the number of days taken into account for the calculation, with the aim of reinforcing the importance of the threshold. Therefore, many previous studies have increased the durationduration of this time window, going from the initially recommended 5 days to 31 days.

Did you know?

The so-called hot days correspond to the 10% of the hottest days in a given region.

What researchers from the University of Vienna demonstrate today is that such long time windows cause the threshold calculation to conflict with the seasonal cycle. Depending on the region, this can lead to an underestimation of the probability of extremes occurring. Please understand that the expected frequency of hot days is underestimated.

The study carried out by researchers at the University of Vienna (Austria) shows that if an error in climate calculations is not corrected, hot days will be underestimated by up to 30% in 30 years. In other words, today only 70% of real extreme temperatures are detected in some regions. © Lukas Brunner, University of Vienna, CC by

The error decreases with the magnitude of the heating.

There peninsulapeninsula Arabia and the western United States would be among the regions most affected by the problem. In these regions, the researchers estimate that the algorithms only detect 7% of the hottest days instead of 10%. This is a relative error of 30%. For Europe, on the other hand, there would be no mistake in this matter.

The researchers also point out that in the context of global warming that we are experiencing, the error trend could finally be reversed. In fact, the most sensitive regions will experience extreme temperatures almost every day of the year by the end of this century. Therefore, the greater the warming, the more the discovered underestimation will decrease. Which will ultimately lead to an overestimation of the change signal. Because historically only 7% of days were counted as hot instead of 10%.

The authors of the study thus propose to their colleagues a correction that would almost completely eliminate the error. Sufficient to better characterize extreme temperature changes in the context of global warming.

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