Pollen grains from flowering plants were meant to fly, sometimes hundreds of miles on the wind. Now it seems that the climate crisis has accelerated travel, causing allergy season in some parts of the world to start earlier, last longer, and become more severe every year.
Over the past three decades, warmer temperatures due to climate change have caused North America’s pollen season to grow by as much as 20 days a year. At the same time, higher CO2 levels mean that more pollen is generally produced in the spring. Similar trends have also been noted in Europe.
This increase in pollen aggravates all kinds of respiratory problems for people with allergies, but there is another phenomenon that is often overlooked.
New research in southeastern Germany has found that the way pollen is transported in a warming world is also changing due to weather patterns and atmospheric circulation, potentially spreading pollen to new areas and exposing people to various allergens for which their immune systems are not prepared.
The study focuses on the state of Bavaria in Germany and uses six pollen monitoring stations in the region to track seven species of flowering plants.
From 1987 to 2017, the authors found that certain species, such as hazel bushes and alder trees, extended their blooming season by up to 2 days per year, adding up to 60 days in the pollen season in Bavaria during that time. During the same period, other plant species, such as birch and ash trees, have started to bloom and release their pollen 0.5 days earlier per year.
Most surprising, however, is how much of that pollen was non-native. At alpine monitoring stations, 75 percent of the pollen species came from outside Bavaria. At lowland stations, 63 percent was 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 being released from other parts of the world during the day and at night, extending local allergy seasons and making them more variable towards the end of spring.
The findings are consistent with another recent study, which took place across Europe, and found that pollen transport alone is responsible for up to 20 percent of recent changes in grass pollen and up to 40 percent of changes in birch pollen. Sometimes these extra charges can even show up at night, a time usually considered safe for allergic people to air out their homes.
“Pollen transport has important implications for the length, timing and severity of the allergen pollen season,” says eco-climatologist Ye Yuan of the Technical University of Munich.
The study in Bavaria is one of the first regional studies on this topic, and it suggests that even before spring, pollen transport from elsewhere in the world is not unheard of.
Between 2005 and 2015, the authors found that preseason pollen was commonplace, even if that particular plant was not yet blooming in Bavaria. In fact, many non-local pollen emerged at least 10 days before local sources.
“Even during the main pollen season, 70 percent of the pollen season start dates were linked to transportation,” the authors write, suggesting that the pollen season is “only weakly dependent on local pollen blooms”.
Where exactly all that non-native pollen comes from is another issue that’s beyond the scope of this particular study, but it’s worth investigating in the future.
“We were surprised that pre-season pollen transport is a fairly common phenomenon, seen in two-thirds of cases,” admits ecoclimatologist Annette Menzel, also from the Technical University of Munich.
Taking this factor into account, the pollen season could be even longer than previous estimates, Menzel adds.
Pollen allergies already affect 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 pollen to new areas (where people are not sensitized) can cause the problem, so much worse.
“Especially for lightweight allergen [pollen]”Long-distance transport can seriously affect local human health,” said Yuan.
We just don’t know yet.
The study is published in the Limits in allergy.