Are some seasons disappearing from our lives?

Climate change is a well-known topic for most people nowadays, being present in a considerable proportion of conversations worldwide. Albeit scientists have a data-based perception of the global climate change, most people relationship with it is based on their daily experiences and memories, which can be unreliable especially in the medium and long ranges. One statement commonly heard by the authors in relation to people’s experience with climate change is that intermediate seasons are retreating, leading to a cold-hot season dipole. This work aims to verify if data confirm this general perception using quality-controlled observational data. In this study, we select over 1000 climatological stations around the world and analyse the trends in the number of days belonging to each climatological season. For a station to be selected, a simple two-step procedure is followed to ensure the reliability of the trends computation: 1) any year with at least 20 days without data is removed from the time series; 2) then, if a station has less than 8 years with remaining data in any decade, that station is discarded from the selection. Once station selection is performed, the number of days belonging to one season is computed by creating a yearly cycle of temperature using data between 1955 and 1984 as climatological reference period. Then, the days belonging to a climatological season are computed as follows for the northern (southern) hemisphere stations: a) days with a temperature above (below) the climatological mean of June 1^st are considered summer (winter) days; b) days with a temperature below (above) the value of the climatological mean of December 1^st are considered winter (summer) days; c) values in between have been considered as spring or autumn days, depending if they occur before the yearly higher peak of temperature, or after it. Both daily maximum and minimum temperatures, and several reference periods, are used for the analysis with similar results in all cases. We find that, in general, the durations of intermediate seasons have remained steady or slightly increased since 1955 around the world, in contrast with the popular feeling. Furthermore, the length of summer has increased in Europe, Australia and China at a rate of 3-4 days/decade in average, whereas the number of winter days has decreased in those regions at a rate of between 5 and 10 days/decade. However, these trends are not as clear in the continental United States of America, with a region in central USA with a reverse trend –longer winters and shorter summers. These findings highlight the importance of data availability for climatological studies and discussions and reveal an area of interest inconsistent with the general global trend, which should be further studied.