If you felt like your allergies came earlier this year, you are probably right. Analysis of 97 European pollen monitoring stations over 40 years (Ziello et al., 2012) found that the birch pollen season has advanced by 7-14 days since the 1970s in central and northern Europe.
What changed
Warmer late-winter temperatures are the dominant driver. Birch, oak and alder all bud when accumulated heat exceeds a species-specific threshold. As that threshold is reached earlier in the year, pollen release follows.
The length of the season has not changed as much as its timing. However, higher average CO2 concentrations have been shown in greenhouse experiments to increase pollen production per plant, especially in ragweed (Ziska & Caulfield, 2000).
Why it matters for health
Earlier seasons push allergy care into an overlap with winter viral infections, which complicates both diagnosis and treatment. The French immuno-allergology society reports a measurable increase in consultations for rhinitis in February since 2010, largely driven by cypress and early-onset birch.
"Climate adaptation for allergy sufferers starts with a longer surveillance window. What used to be a March-to-May concern now spans January to November if you count ragweed."
How to use ClearSpot year-round
Keep the "pollen" sensitivity enabled even outside the traditional spring window. Our module switches between CAMS forecasts (high spatial resolution, short horizon) and RNSA historical reference data (lower resolution, longer horizon) so the verdict stays meaningful whether you are checking today or planning a holiday in four months.