Background Ongoing climate change might, through rising temperatures, alter allergenic pollen biology across the northern hemisphere. We aimed to analyse trends in pollen seasonality and pollen load and to establish whether there are specific climate-related links to any observed changes.Methods For this retrospective data analysis, we did an extensive search for global datasets with 20 years or more of airborne pollen data that consistently recorded pollen season indices (eg, duration and intensity). 17 locations across three continents with long-term (approximately 26 years on average) quantitative records of seasonal concentrations of multiple pollen (aeroallergen) taxa met the selection criteria. These datasets were analysed in the context of recent annual changes in maximum temperature (T max ) and minimum temperature (T min ) associated with anthropogenic climate change. Seasonal regressions (slopes) of variation in pollen load and pollen season duration over time were compared to T max , cumulative degree day T max , T min , cumulative degree day T min , and frost-free days among all 17 locations to ascertain significant correlations.Findings 12 (71%) of the 17 locations showed significant increases in seasonal cumulative pollen or annual pollen load. Similarly, 11 (65%) of the 17 locations showed a significant increase in pollen season duration over time, increasing, on average, 0•9 days per year. Across the northern hemisphere locations analysed, annual cumulative increases in T max over time were significantly associated with percentage increases in seasonal pollen load (r=0•52, p=0•034) as were annual cumulative increases in T min (r=0•61, p=0•010). Similar results were observed for pollen season duration, but only for cumulative degree days (higher than the freezing point [0°C or 32°F]) for T max (r=0•53, p=0•030) and T min (r=0•48, p=0•05). Additionally, temporal increases in frost-free days per year were significantly correlated with increases in both pollen load (r=0•62, p=0•008) and pollen season duration (r=0•68, p=0•003) when averaged for all 17 locations.Interpretation Our findings reveal that the ongoing increase in temperature extremes (T min and T max ) might already be contributing to extended seasonal duration and increased pollen load for multiple aeroallergenic pollen taxa in diverse locations across the northern hemisphere. This study, done across multiple continents, highlights an important link between ongoing global warming and public health-one that could be exacerbated as temperatures continue to increase.

No abstract

In many perennial wind‐pollinated plants, the dynamics of seed production is commonly known to be highly fluctuating from year to year and synchronised among individuals within populations. The proximate causes of such seeding dynamics, called masting, are still poorly understood in oak species that are widespread in the northern hemisphere, and whose fruiting dynamics dramatically impacts forest regeneration and biodiversity. Combining long‐term surveys of oak airborne pollen amount and acorn production over large‐scale field networks in temperate areas, and a mechanistic modelling approach, we found that the pollen dynamics is the key driver of oak masting. Mechanisms at play involved both internal resource allocation to pollen production synchronised among trees and spring weather conditions affecting the amount of airborne pollen available for reproduction. The sensitivity of airborne pollen to weather conditions might make oak masting and its ecological consequences highly sensitive to climate change.

The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRaP URL' above for details on accessing the published version and note that access may require a subscription.

No abstract