If You're Sneezing More From Pollen, Climate Change Could Be the Culprit
Flowers are beginning to bloom, trees are turning green again and the sun is shining. But if you’re like almost one-third of people in the United States, you might be noticing watery eyes, a tickly throat and a runny nose. That’s right, spring is finally in the air, but so is the pollen that’s gearing up to make your life a bit more miserable over the next few months.
It gets worse: with climate change shifting our weather patterns and causing an early, more extended pollen high, we could all be sneezing more than usual this year.
Pollen: a pervasive problem
Hay fever isn’t new, and it’s increasingly common; an estimated 30 percent of the U.S. population suffered from hay fever, or allergic rhinitis, in 2000, up from just 10 percent in 1970. The National Health and Nutrition Examination Survey (1988−1994), which collected information from nearly 40,000 people in the US, showed that 26.9 percent and 26.2 percent of the population were allergic to perennial rye grass and ragweed respectively—at least twice as high as the previous survey (1976−1980).
It’s pollen that’s to blame for their symptoms. When plants reproduce, they have to get their sex cells together. Pollen carries the male sex cells so it has to be transferred to the female plant. Many plants use insects, like bees, to transfer their pollen to other plants, and others rely on wind. The plants that are wind pollinated produce tiny, light pollen that can be carried on a breeze—fantastic for their reproduction, disastrous for our respiration.
When you inhale pollen grains, they can kickstart an immune response in which your body is trying to attack them. Your immune system overreacts to the harmless pollen: the sneezing, the eye-watering and the histamines that make your nose itchy are designed to kill or eject the pollen. If you’re prone to allergic rhinitis, the more pollen you’re exposed to, the worse your symptoms.
Not every hay fever sufferer is allergic to every pollen. It tends to be seasonal—in the spring, tree pollens like those from the birch, oak and mountain cedar cause the most problems, followed by grass and weeds like mugwort and nettle in the summer, with weeds like ragweed and fungus spores following in the autumn.
But one major factor is having an impact throughout the year: climate change is causing an increase in pollen release, and it’s even making some pollens more potent hay fever inducers. In 2015, the World Allergy Organization, a group of 97 medical societies from around the world, released a statement warning that climate change will have an impact on when, how long and how bad the pollen season will be.
Warmer weather, more pollen
The first culprit is the rise in temperature we’re seeing as a result of climate change. “We have got good evidence of this—global warming due to climate change induces more airborne pollen,” said Amena Warner, Head of Clinical Services at Allergy UK. “Pollen seasons are extending because of the warmer weather, which is having an impact on how much airborne pollen there is circulating.”
A 2015 study showed that in the decade between 2001 and 2010 in the US, pollen season started on average three days earlier than it did in the 1990s. What’s more, the amount of airborne pollen increased by more than 40 percent. “These changes are likely due to recent climate change and particularly the enhanced warming and precipitation at higher latitudes in the contiguous United States,” concluded the researchers.
This is also probably increasing the number of people suffering with hay fever. Scientists predict that by 2050, the number of people with allergic rhinitis in Japan will increase by 40 percent because of local temperature increases: Tokyo’s mean yearly temperature has risen by 3°C since 1890 and is set to hit 3.5°C by 2100.
More CO2 is feeding the pollen problem
While warmer temperatures are leading to earlier and longer pollen seasons and even more potent pollen, rising CO2 levels are also helping plants produce more pollen. Plants feed on CO2, so when there’s an abundance of it, they can go wild producing pollen. Couple that with warmer temperatures, and you’ve got the ideal growth and reproduction conditions for plants, which means more allergens for us.
Take the invasive and highly allergenic plant ragweed, for example. Lewis Ziska and his colleagues at the US Department of Agriculture (USDA) grew ragweed in the lab, under three conditions: pre-industrial levels of CO2, current levels and the higher levels we expect to see in a few decades. They found that exposure to current levels increased the amount of pollen the ragweed produced by 131% compared to pre-industrial CO2, and under predicted CO2 levels this shot up to 320 percent.
Ziska says the intensity of an allergic reaction depends on how much pollen is released, the duration of the exposure and how allergenic the pollen is. In ragweed, these three factors work strongly together. “What’s unique about ragweed is that it produces so much pollen—roughly a billion grains per plant,” he wrote in Environmental Health Perspectives. “And the Amb a 1 protein [in the pollen coat] is also highly reactive with the immune system.”
No escape to the city
One might be tempted to think hay fever would be less of a problem in the city, away from all the trees and weeds, but the opposite appears to be true. Similar results have been observed outside the lab: in downtown Baltimore, where it’s 3ËšC warmer and has 30 percent more CO2 than the countryside, ragweed “thrived, growing bigger and puffing out larger plumes of pollen than its country counterpart,” reported Rachel Becker in The Verge.
Ragweed may thrive in our cities, but there’s a bigger—and taller—problem: the trees planted to provide shade and beauty are making our allergies worse.
“Many people believe that the more trees you have in a city’s green infrastructure, the more they act as a biofilter,” said Amena Warner of Allergy UK. “But are they the right kind of trees? In urban areas, particularly in London, there’s a lean towards planting birch trees, which are highly allergenic. When they’re in cities, people can’t escape the pollen easily, and it’s virtually indestructible unless it’s wet.”
That means the pollen that collects on your clothes, the bottom of your shoes and in your hair during your afternoon stroll could plague you until it rains or is washed away. That, says Warner, extends the time you’re in contact with pollen, even out of pollen season. The U.K. has the third highest rates allergic rhinitis and asthma prevalence in the world, so Allergy UK is seriously concerned about this.
“It’s important that the right tree is planted in the right place,” said Warner. “We want to raise awareness of why planting allergenic birch trees in urban areas can increase hay fever and other respiratory conditions.”
So if we know the pollen from birch trees (and lots of others) is causing allergic reactions, why are they still dominating our city streets? “Mainly because they seem to be fashionable,” said Warner. “They have this lovely silvery bark, and they’re long and graceful with a beautiful sweeping canopy that gently sways in the wind. And they don’t drop fruit—in a city, you want trees with a low cleanup cost.”
Keeping hay fever at bay
There are alternatives—not all tree pollen is allergenic. In 2010, a report by the National Wildlife Federation called on states, communities and homeowners to “undertake smart community planning and landscaping, with attention to allergenic plants and urban heat island effects, to limit the amount of pollen and other allergens that become airborne.”
One way to reduce the impact of hay fever in cities would be to use the OPALS (Ogren Plant Allergy Scale), which rates trees in terms of how allergenic they are, to choose less allergenic trees. So when you’re choosing your tree, whether it’s in your garden or on the street, opt for something that won’t make people sneeze.
As the climate continues to change and we see an increase in hay fever, we’ll also notice a bigger impact on public health, not least because an estimated 30 percent of people with allergic rhinitis develop asthma later on. While urban planning may be out of our hands, there are some things we can do to reduce the pollen problem.
David Mizejewski, a naturalist at the National Wildlife Federation and a long-time allergy sufferer, gave readers of the Federation’s 2010 report some advice:
- Get an allergy test—that way you can decide when’s best to go outside
- Ask your doctor about allergens and what medication to take
- Check daily pollen counts and go out when they’re low
- Wash your clothes and yourself to remove trapped pollen, and use nasal sprays
- Choose non-allergenic plants for your garden
- Plant female trees and shrubs (it’s the males that produce pollen)
It’s important to remember that people with allergic rhinitis can develop asthma, which can be serious. So if your symptoms start to affect your breathing, it’s best to consult a doctor.