Pollen grains from flowering plants were meant to fly, sometimes travelling hundreds of kilometres on the wind. Now it appears the climate crisis has accelerated that travel, making allergy season in some areas of the world start earlier, last longer, and get more severe each year.
In the past three decades, warmer temperatures from climate change have caused pollen season in North America to grow by as much as 20 days per year. At the same time, higher CO2 levels mean more pollen is produced overall in springtime. Similar trends have also been noticed in Europe.
This increase in pollen is exacerbating all sorts of respiratory problems for those who are allergic, but there's another phenomenon at play that's often overlooked.
New research in the southeast of Germany has found the way pollen is transported in a warming world is also changing with weather patterns and atmospheric circulation, potentially spreading pollen to new areas and exposing people to different allergens their immune systems are unprepared for.
The study focuses on the state of Bavaria in Germany, and uses six pollen monitoring stations in the region to track seven types of flowering plants.
From 1987 to 2017, the authors found certain species, like hazel shrubs and alder trees, have extended their flowering season by up to 2 days per year, adding up to 60 days to the pollen season in Bavaria in that time. Over the same time period, other plant species, like birch and ash trees, have begun to flower and release their pollen 0.5 days earlier each year.
What is most surprising, however, is how much of that pollen was non-native. At alpine monitoring stations, 75 percent of pollen species were from outside Bavaria. At lowland stations, 63 percent were related to non-local pollen sources, and that was true even in Bavaria's main pollen season.
"This means that the actual pollen concentration is less dependent on local conditions," the authors write, and more dependent on interregional wind and atmospheric patterns.
Changes in pollen transport could mean more pollen delivered during the day and at night from other areas of the world, extending local allergy seasons and making them more variable towards the end of spring.
The findings fall in line with another recent study, which took place across all of Europe, and found pollen transport alone accounts for up to 20 percent of recent changes in grass pollen and up to 40 percent of changes in birch pollen. Sometimes these extra loads can even show up at night, a time typically considered safe for allergic people to air out their homes.
"The transport of pollen has important implications for the length, timing, and severity of the allergenic pollen season," says eco-climatologist Ye Yuan from the Technical University of Munich.
The research in Bavaria is one of the first regional studies on the subject, and it suggests even before spring, pollen transport from elsewhere in the world is not unheard of.
Between 2005 and 2015, the authors found pre-season pollen was commonplace, even when that particular plant was not yet flowering in Bavaria. In fact, many non-local pollens were showing up at least 10 days before local sources.
"Even within the main pollen season, 70 percent of pollen season start dates were linked to transport," the authors write, and this suggests pollen season has "only a weak dependency on flowering of local pollen sources."
Where exactly all that non-native pollen is coming from is another matter beyond the scope of this particular study, but it's something worth investigating in the future.
"We were surprised that pre-season pollen transport is a quite common phenomenon, being observed in two-thirds of the cases," admits eco-climatologist Annette Menzel, also from the Technical University of Munich.
When taking this factor into account, pollen season may be even longer than previous estimates, Menzel adds.
Already, pollen allergies impact up to 40 percent of the population in Northern Europe, and recent studies suggest that higher pollen concentrations, longer pollen seasons and the spread of pollens to new areas (where people are not sensitised) could make the problem so, so much worse.
"Especially for light-weight allergenic [pollen], long-distance transport could seriously influence local human health," argues Yuan.
We just don't know to what extent quite yet.
The study was published in the Frontiers in Allergy.