A recent study published by the National Academy of Sciences shows not only is anthropogenic climate change worsening the North American pollen season, it’s also prolonging it.

The research focused on four pollen metrics at 60 North American pollen stations over the span of 28 years (1990-2018). Observed variables included total pollen count, pollen season start date, pollen season length and pollen count extremes.

Research results

The results of the study showed there was an approximate 20% increase in spring (February–May) and annual pollen counts, with the largest increase in Texas and the Midwest. The allergen with the most significant increase was tree pollen.

IN-DEPTH: The Austin area’s only certified Allergy & Asthma clinic confirmed two record-setting spikes in cedar this winter.

Changes in season were also observed, with the average start date of pollen season coming ~20 days earlier and lasting eight days longer.

Figure A: annual pollen count trend
Figure B: pollen season start date trend

Why it matters?

Both the increase in pollen concentration and season duration results in an increase in exposure time for those who suffer from pollen allergies.

In addition, long-term data shows significant increases in allergies across all age groups in the United States, with trends of increasing pollen sensitivity in kids leading to increased adults with allergic asthma. Both asthma and allergies are said to account for “substantial morbidity burdens” and hefty medical costs every year.

Further explanation of models and research process

Researchers used climate models to analyze the cause and effect relationship between climate change and pollen counts. The model included eight climate variables, including temperature, precipitation, frost days and atmospheric CO2 concentrations, to test four pollen metrics: annual pollen count, spring pollen count, pollen season start date and pollen season length.

The models explained 51–90% of the variance in pollen metrics, with temperature found to be the primary driver of pollen variability.

A different set of models was used to determine the role of human-caused climate change on the same four metrics. This was done by combining the output of 22 Earth system models to calculate the signal of human influence on the pollen variables. This set of model runs showed anthropogenic forcing was a strong driver of trends in pollen season and a modest driver of trends in pollen counts.

For more information on the study, click here.