Climate-driven changes in pollen dynamics: increased loads and earlier, longer exposure

There is unequivocal evidence that the climate is changing, and it is generally accepted that the trend will continue. Climate change is relevant to public health, as it can lead to alterations in the distribution and flowering phenology of plants and to changes in pollen exposure, with subsequent impacts on human health. The primary objective of this paper was to provide a quantitative synthesis of the available literature on the evolution of pollen season intensity and timing in plants with a higher allergenic potential. Six botanical families have been studied: Betulaceae (birch, hazel, alder), Cupressaceae, Oleaceae (olive, ash), Poaceae, Urticaceae, and Asteraceae (mugwort, ragweed). Three main indicators of the potential impact of climate change on pollination have been retained: the pollen integral, the start date of the pollen season, and the duration of the pollen season. The outcome is a dominant trend toward earlier and more abundant pollen seasons, particularly for trees that flower in winter and spring. In contrast, trends for grass or weeds that pollinate later are less consistent and often region-specific. The variations recorded are taxon-, site-, and period-dependent, with some species even showing opposing trends within the same botanical family, illustrating the complex interactions between biological adaptation and climatic variability. While the current influence of climate change on pollen production and phenology is well established, the magnitude of its future impact remains uncertain, and the diversity of methodologies and study durations limits the comparability of available data. Nevertheless, most projections support a continued, though possibly attenuated, increase in pollen intensity and season advancement. In any case, when combined with likely qualitative and quantitative changes in the concentration of allergens in pollen grains, the identified trends may already have, and will very likely continue to have, an impact on both allergic sensitizations, the prevalence of seasonal symptoms, and their severity, thus affecting their diagnosis, prevention, and treatment.