April 22, 2024

Every few years scientists re-confirm, through new research, that airborne pollen has substantial respiratory health impacts and that anthropogenic or man-made climate change is known to exacerbate these impacts by increasing concentrations of pollen and extending pollen seasons.1

Studies conducted in both greenhouse and field settings have shown a link between pollen levels and rising temperatures, indicating a need for public health policies and awareness raising regarding anthropogenic climate change's role in pollen seasons.2,3,4 Such a shift in the environment is uniquely foreboding as it has been suggested that it can adversely affect human health by contributing to rises in allergic respiratory diseases such as allergic rhinitis and asthma.5

The HCPLive editorial team regularly interviews experts in the medical field with the aim of raising awareness of various health concerns and informing clinicians on such topics. This feature article represents a deep dive into the subject of climate change in honor of Earth Day, specifically in its adverse relationship to allergic disease.

In this video series, 3 experts were featured to discuss such issues and to highlight research on the causative relationship linking air pollution, rising temperatures, and prevalence of different allergic conditions.

The team spoke with David B. Peden, MD, the Harry S. Andrews professor of pediatrics, medicine and microbiology/immunology and associate director of the Center for Environmental Medicine, Asthma & Lung Biology at the University of North Carolina (UNC) School of Medicine. We also interviewed Elizabeth Cerceo, MD, associate internal medicine program director and the director of environmental health in the division of hospital medicine at Cooper University Health Care.

Lastly, we spoke with Lewis Ziska, PhD, an associate professor of environmental health sciences at the Mailman School of Public Health at Columbia University and the Climate and Health Certificate Lead. Ziska, Peden, and Cerceo each are leading experts in their fields and have contributed their views and research on this topic throughout their careers.

Given the surge of interest around the dangers of anthropogenic climate change and the rising incidence of allergic diseases in industrialized countries, these 3 interviews posted above highlight several key topics regarding new research, public health needs, and changing perceptions regarding humanity’s shared impact on the health of the planet.

Here are several notable quotes from the 3 interviews on the topic of climate change and its effects regarding allergic conditions.

On Pollution and Its Impact on Climate Change

Peden: What's pretty clear is that manmade air pollution is a singular driver to the changing climate that we're seeing now. The carbon footprint is essential and it becomes a cycle. What happens is that as you have man-made pollutants, you change climate, you have you have a warmer climate, and that changes the likelihood that pollutants are going to be produced, then you're going to get more pollutants, that then changes the climate, so it becomes a little bit of a cycle…Fossil fuel, combustion, is clearly the most significant driver of climate change that we have.

Cerceo: There's really two prongs to it. When we combust fossil fuels, it both releases the greenhouse gasses that accelerate climate change and global warming. Then there's the direct effect from all of those pollutants, those things that we breathe in, that we eat, and that we consume. All of those have impacts on our health and wellbeing.

The (Environmental Protection Agency) has designated 188 hazardous air pollutants, and these are known bad actors. These are things like acrolein, benzene, cadmium, mercury, and we know that these are not good for our health. Then there's the criteria air pollutants and those are 6 things that affect more broader air quality. Those are things like particulate matter, 2.5, or PM2.5. Things like ozone, oxides of nitrogen, sulfur dioxide, but it also encompasses lead and carbon monoxide.

Ziska: Right now, there are efforts to try and address what's happening in regard to fossil fuel emissions and efforts in regard to public health, but very little at the governmental level. I think if you looked at all of the money that the National Institute of Health spent in the last 3 years on average each year, they're spending about $12 million. That's a million, not a billion. So these issues related to the climate and health are obviously important, and pollen is just one aspect of that. But you can look at air quality, you can look at heat stress. There's so many more aspects of this that we just don't really have a full grasp on yet. I think there's a lot more that we need to know.

On Climate Change's Effect on Pollen Allergies

Peden: What has happened is that as you have a warmer climate, 2 things occur. One, the pollination season is longer, so in the American northeast, what used to be a relatively robust but brief pollen season now has spread out several weeks longer than it used to be. That's all because you have mild falls, milder winters, and it goes into spring. So spring kind of begins earlier and it lasts longer. You end up having a longer time for plants to pollinate.

The most robustly-studied of those is ragweed and ragweed pollen. But in fact, tree pollen also behaves much the same way. Birch has been studied in Europe. Basically, any flowering plant that requires airborne pollination. In flowers that require insects, that pollen is usually not the issue. But airborne pollination really is the problem.

Cerceo: If we dial in on allergies in particular, allergies are a huge problem. Globally, about 30% of adults and about 40% of children have allergies, nasal polyps, and it's projected that by 2050, there's going to be 4 billion people with allergies. There's a lot of reasons for that. First, with climate change and global warming, we see at higher temperatures that these allergenic plants flourish. They go into regions where they weren't before. They have longer growing seasons and there's earlier springs.

There's actually a great interactive article in the Washington Post, where you can see these early springs that are really in a U-shape across almost all of the US. There's a little tiny swath in the Upper Midwest that it's not affecting yet. But for so many of us, we're seeing early springs, and we're seeing longer allergenic seasons, sometimes by up to 28 days. The other problem is that as you have higher CO2 concentrations, that actually propagates more pollen and that pollen is more allergenic. Specifically, it impacts the Amb a 1 protein, and it makes it even more potent.

Ziska: One of the things that's happening with rising carbon dioxide is it also directly affects the chemistry of plants and one of the effects that we're seeing is for ragweed, which is some of my work. Dr. Oh, the head of pediatric allergy in South Korea, was looking at it for oak trees. In both cases, what we saw was that as CO2 increases, the protein on the surface of the exine, the exine—which is the outer outer shell of the pollen protein that causes the immune system to respond and causes your allergies—is increasing. Basically, what rising CO2 is doing is changing the chemistry in a way that makes the pollen more allergenic.

So when you add that to the other 2 facets…the direct effects of rising CO2, as well as the indirect effect of rising CO2 relative to temperatures, are going to affect the amount of pollen that's going into the air. The amounts of pollen in the air, in turn, are going to affect your respiration, your allergies, and so forth. For myself, I carry a rescue inhaler around that was made during the spring and the fall, because my allergies are severe enough that I can get asthma. We know that the amount of pollen, the kind of pollen, will have respiratory effects that depending on the individual may become exacerbated to asthma and often COPD and other health issues.

On Public Awareness and Clinicians’ Responsibilities in Awareness-Raising

Peden: You have commercials for antihistamines, you have commercials for over-the-counter or other corticosteroids. You have commercials for drugs that focus on treating allergies. The truth of the matter is that part of that is because there's a marketplace for those, but part of that marketplace is that there's a broader public perception that there's a longer and more robust pollination season. I think conversationally, many people comment on and are aware that pollen season goes longer, noticing the springs and that ragweed season has been worse than usual. I do think especially in the past 5 years, I think people have really begun to understand that. There's more press attention to climate change.

Cerceo: There's a lot of really compelling research into climate change communication. Fortunately, many more Americans are now recognizing that climate change is a problem and that it impacts their health directly. I'll refer you to some great research by Ed Maibach. It's called ‘the Six Americas.’ So looking at those portions of the population that are alarmed, that are concerned and cautious, those segments of the population have really increased such that it's almost 80% of the population.

Now, one of the things we really need to do as physicians, though, is make those tangible linkages to how things like allergies, things that many of us experience, are linked to climate change and air pollution. (We have to) really make that clear, so people understand how to take care of their health, how to advocate for themselves, and how to vote for policies that are going to be beneficial for their health and that of their communities.

Ziska: I think that if you ask folks and don't include the phrase ‘climate change,’ if you just ask them “Are you seeing an effect in terms of your allergies? Are you seeing an effect perhaps in your neighbors?” Most of them will say yes. In part because of the political differences, if you use the phrase ‘climate change’ in that regard, they may say, “No, it's not related to climate change.” So it's a hard question to really address per se.

The quotes contained in this article were edited for the purposes of clarity. For further information, view the interviews posted above.


  1. Anderegg WRL, Abatzoglou JT, Anderegg LDL, Bielory L, Kinney PL, Ziska L. Anthropogenic climate change is worsening North American pollen seasons. Proc Natl Acad Sci U S A. 2021 Feb 16;118(7):e2013284118. doi: 10.1073/pnas.2013284118. PMID: 33558232; PMCID: PMC7896283.
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