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Visualize the alteration of the seasons with this infographic

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In recent decades, the seasons that shape the meteorological landscape of temperate latitudes have experienced a notable alteration. With climate change continuing at the current rate, a much deeper mutation is now looming. In any case, this is what the results of a new study published in the scientific journal reveal. Geophysical research letters.

Many seasonal mechanisms are already severely impacted by global warming. The most striking changes are probably in the living world. Let us quote for example the evolution of the phenology of the plants or that of the dates of migration of birds and insects.

These modulations are of great concern because ecosystems behave like functional units. However, climatic disturbances affect the species that constitute them in many ways. Also, the relationships between organisms become deregulated, causing a more or less profound alteration in the functioning of ecological communities. Changes that end up affecting our lives directly or indirectly – a simple example being the lengthening of the pollen season.

Are there really no more seasons?

A study published on February 19 addressed the question of the changing seasons from a hitherto unexplored angle. Indeed, the authors evaluated how the four seasons of the temperate latitudes of the northern hemisphere (30 ° N – 60 ° N) have changed and will change by the end of the century.

Trend in duration (left) and the beginning of the seasons. Spring (a, e), summer (b, f), fall (c, g) and winter (d, h) show changes consistent with global warming. Credits: Jiamin Wang et al. 2021.

Spring, summer, autumn and winter were defined over the period 1952-2011 according to temperature thresholds. Winter was calculated as the 25th percentile of the annual temperature distribution and summer as the 75th percentile. The spring and fall seasons have been deduced based on the first two. Thus, the researchers had a benchmark to assess changes in length and beginning of the above four entities.

For the past evolution (1952-2011), the results reveal a lengthening of the hot season and a contraction of the cold season. More specifically, summer has gone from 78 to 95 days and winter from 76 to 73 days. As for the inter-seasons, they have both been reduced. The authors found a duration that went from 124 to 115 days for the spring and from 87 to 82 days for the fall. There is in fact a transition to a diagram bi-seasonal marked by an extended warm period, a relatively short cold period and faster transitions between the two. Finally, spring and summer start earlier while fall and winter come later. Work that makes it possible to objectify and quantify a general feeling experienced on the scale of the hemisphere.

Climate: 6 months of summer by 2100

To anticipate the future, the researchers used climate models from the project CMIP by prescribing continued warming at the current rate. In doing so, they found that in such a scenario, summer would last almost half the year. On the contrary, winter would last for less than two months. It goes without saying that such a seasonal clock would have major environmental, socio-economic and health impacts.

seasons
Schematic representation of the duration and start date of the four seasons in 1952, 2011, 2050 and 2100. Summer is in ocher, winter in turquoise and the intermediate seasons in white (green leaf for spring, brown for autumn). Finally, the months are indicated outside the circles. Credits: Jiamin Wang et al. 2021.

“Numerous studies have already shown that the changes in the seasons entail significant risks for the environment and health”, notes Jiamin Wang, co-author of the paper. “It is difficult to conceptualize an increase in temperature of 2 or 5 degrees on the global average”, adds Scott Sheridan, a climatologist who was not involved in the study. “But I think realizing that these changes will lead to potentially dramatic season shifts probably has a much bigger impact on how you view what climate change is doing.”.

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