Anthropogenic climate change is worsening North American pollen seasons

Abstract

Airborne pollen has major respiratory health impacts and anthropogenic climate change may increase pollen concentrations and extend pollen seasons. While greenhouse and field studies indicate that pollen concentrations are correlated with temperature, a formal detection and attribution of the role of anthropogenic climate change in continental pollen seasons is urgently needed. Here, we use long-term pollen data from 60 North American stations from 1990 to 2018, spanning 821 site-years of data, and Earth system model simulations to quantify the role of human-caused climate change in continental patterns in pollen concentrations. We find widespread advances and lengthening of pollen seasons (+20 d) and increases in pollen concentrations (+21%) across North America, which are strongly coupled to observed warming. Human forcing of the climate system contributed ∼50% (interquartile range: 19-84%) of the trend in pollen seasons and ∼8% (4-14%) of the trend in pollen concentrations. Our results reveal that anthropogenic climate change has already exacerbated pollen seasons in the past three decades with attendant deleterious effects on respiratory health.

Keywords: Earth system model; attribution; climate change; detection; respiratory health.

Fig. 1.

Detection of long-term worsening of pollen seasons in North America. Linear trend over individual stations of the annual pollen integrals (A) and pollen season start date (B) across the 60 pollen stations in North America. Warm colors indicate increasing annual pollen integrals or earlier start dates and circle size is proportional to the years of data at each station.

Fig. 2.

Temperature strongly influences pollen seasons and loads in North America. Predicted slope from linear mixed effects models across 60 North American cities of annual average temperature against the total annual pollen integrals (A), pollen season start date (DOY) (B), total spring (February–May) pollen integrals (C), and total pollen season length (days) (D). Points are individual years at individual stations. Thin lines are station-level trends. Point/line colors are regions (SI Appendix, Fig. S5). Shaded areas indicate the 95% CI of the fixed effect.

Fig. 3.

Anthropogenic climate change (ACC) has exacerbated pollen seasons. Boxplot of the percentage contribution of ACC to the long-term (1990–2018) and more recent (2003–2018) trends of annual total pollen integrals (dark red) and spring total pollen integrals (red) (A) and pollen season start date (dark green) and season length (light green) (B) across 60 pollen stations in North America. Data are plotted from 22 climate models (i.e., each model’s estimated fractional contribution to the observed continental trend from the mixed effect model).