Summers expected to warm faster than winters with climate change

Summers expected to warm faster than winters with climate change
Summers expected to warm faster than winters with climate change

In a warmer climate than the one the Earth currently experiences, summers heat up more quickly than winters, concludes a study led in particular by Niels de Winter, an Earth scientist working at the VUB. The research analyzed the composition of fossil shells dating from the Pliocene period, around three million years ago, when the Earth’s average temperature was warmer than now.

When the past sheds light on our future

The study, published in the scientific journal Science Advances, measured the chemical composition of fossil shells, found during the construction of the Kieldrecht lock, in West Flanders, explains the VUB in a press release Wednesday. These shells come from molluscs (oysters, clams, scallops, etc.), which lived during the Pliocene period in the North Sea. Certain current parts of Flanders and the Netherlands were then submerged. These shellscontain very detailed information that was recorded during their life“, they developed in layers, a bit like tree rings or fingernails.

During the Pliocene, the average temperature on Earth was 2.5 to 3°C higher than today. The researchers have “took a ‘snapshot’ of the climate at the time, to observe the differences between seasons in a warmer climate” than the current one, explains the VUB. To reconstruct the temperature at which the shells formed, the scientists measured the amount of rare heavy isotopes of oxygen and carbon present in a single calcium molecule in the shells. These atoms are in fact more common in shells formed in colder waters.

The study concludes that in a warmer climate, such as that of the Pliocene, warming is greater in summer than in winter. Thus, the temperature in winter had increased by around 2.5°C at that time, and by 4.3°C in summer.

Researchers observe the same phenomenon in models for the future, which predict warming of the same magnitude for the year 2100“, points out VUB. This research therefore allows us to glimpse the future climate in Europe, if the current trend continues. “We can probably expect sharper temperature differences between summer and winter, and the risk of heat waves in summer will increase“, explains Niels de Winter, who also works at the Vrije Universiteit Amsterdam, in the press release. The Brussels Institute of Natural Sciences also participated in the research.

The weakening of the “depression rail”: direct cause of “super summers”

As for the reason for this difference between summer and winter, the study does not dwell on this aspect. But other scientists confirm that this is already a reality. “All seasons are now warmer than at the beginning of the 20th century. But summer heats up more strongly than winter“, Christine Berne, climatologist at Météo France, told France Info.

To find out more about the causes, we must turn to a study carried out by the Weizmann Institute in Amsterdam and published in April 2024. The basic problem seems to be the disruption of the “rail of depressions” which leads to disturbances and cooler temperatures as far as Europe. Normally, this works well thanks to the difference in temperatures between the polar regions, which are very cold, and those further south, which are warmer. Except that with climate change, the North Pole has become the part of the world warming the fastest. Since the contrast between north and south weakens, especially in summer, the track of depressions weakens. Hence the particularly high risk of heat waves during the summer season.

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