© by aha! Swiss Allergy Centre - Info on allergies - Climate and plants - tree in springtimes

The mixture of vegetation is closely matched to the climatic conditions of a region. Different plants colonise an area and thrive depending on temperature, precipitation and moisture. This is why climate has a decisive influence on what plants with allergenic pollen are found in what region.

Plants and Climate

In Central Europe, the six most important plant groups are the grasses, birches, hazel, alders, ashes and mugwort. In the cooler Alpine climate, hazel and ash for instance no longer thrive and mugwort is scarcely to be found. Owing to the low temperatures, most of the plants in the Alps produce less pollen, so that the pollen season there is much shorter and less intense.

The Mediterranean climate is associated with different plant species which are important in terms of allergies: olive tree, cypress and pellitory (Parietaria). The close link to temperature raises the question of what impact climate change will have on the allergy situation.

Climate change – what do we know?

The temperature in Switzerland has risen by about 1.3–1.6°C in the past 100 years. This increase is greater than the global average (0.6°C). Climate specialists expect a temperature rise of 3°C in summer and 2°C in winter by the year 2050. Precipitation levels will decrease in summer and increase slightly in winter. Models show that towards the end of the 21st century every other summer will be as warm and/or as dry as the 2003 heat wave.

What changes in pollen flight can we see today?

  • Time shift in the pollen season: the pollen season of birches and ashes is starting around 2–3 weeks earlier than 20 years ago. The grass pollen season is starting around 10 days earlier.
  • Longer pollen season: lengthening of the pollen season is mainly evident with grass and weed pollen. The tree pollen season has not lengthened so far; it has simply shifted by about two weeks.
  • Increase in quantity of pollen? There is a suspicion that more pollen will be produced in warmer temperatures. In the 20-year pollen measurements for Switzerland, this is still not evident although some measuring stations have recorded larger quantities of certain pollen species than 20 years ago.

What changes can we expect in future?

  • The pollen season continuing to start earlier (may be assumed)
  • A possible increase in pollen quantities? (still uncertain)
  • Possible increase in weed pollen (sorrel, plantain, mugwort, goosefoot) because of greater dryness in summer and more open spaces
  • New allergenic plant species may emerge: possible migration of warmth-loving plants, i.e. allergenic plants from the Mediterranean region (cypress, pellitory – Parietaria), poss. olive. The new allergenic species may lengthen the period of time that allergy symptoms appear or also cause additional people to suffer allergies.
  • Vegetation shift to higher altitudes, i.e. even in the mountains there may be more pollen than we have today because of a warmer climate.
  • Spread of ambrosia and increase in quantities of ambrosia pollen: ambrosia mainly spreads because of human activity, but climate change supports the colonisation of new habitats by ambrosia.

Facts and figures

In Switzerland around 1.2 million people, roughly 20% of the population, are affected. The flower of a single blade of grass contains around 4 million flower pollen grains. Conifers are among the flower pollens that do not trigger any allergy. Visible as a yellow dust-fall in springtime, at most they cause irritation of the conjunctiva.

Author: Dr. Regula Gehrig-Bichsel, Federal Office of Meteorology and Climatology MeteoSwiss

Editors: aha! Swiss Allergy Centre in co-operation with the Scientific Advisory Board. For prevalence figures, see source references.

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