Pollen, allergies and climate change

With the arrival of spring, the good weather doesn’t come alone but it is accompanied by the pollen allergy season. While enjoying the beauty of blossoming nature, a huge percentage of people have to deal with allergy-inducing airborne pollens. Now, because of climate change, the allergy season is about to get even worse.

Pollens and allergies

Pollen is the male reproductive component of plants and, as such, is in theory innocuous. When pollen enters the human body is sometimes attacked like it was a parasite. This is caused by the fact that the protein sequence in pollen is recognised as similar to the protein sequence in parasites by their immune systems. When this happens, their bodies attempt to expel the presumed parasite through sneezing and other symptoms. This reaction against the pollen is what is commonly called as allergy.

The pollen composition that circulates in the air changes during the year with the seasons. In spring, the pollen that gives humans allergies comes mostly from trees. In the summer, grass pollen becomes dominant and becomes the main cause of allergies. At the end end of summer and beginning of fall instead, people begin to suffer from pollinating weeds.

The relation between pollen and climate change

Millions of people suffer from seasonal allergies triggered by airborne pollen, not just in spring but in summer and fall too. In the last decade, evidence suggested their numbers would rise in a changing climate. In 2016, Charles W. Schmidt wrote about the role of climate change in contemporary pollen allergies. He underlined how the warming planet is extending the growing season, and along with it allergy-caused risks to human health.

A new study confirmed that climate change will influence the timing and intensity of anemophilous pollen production. The pollen season beginning might shift to 10-40 days earlier and the end to 5–15 days later, thus lengthening the season duration. As temperature and precipitation alter pollen emission maxima, the amount of pollen produced during the flowering season could rise up to 40% by the end of the century. Similarly, the increasing atmospheric CO2 may increase pollen production emissions by up to 200% in the same time frame. Some trees responsible for allergy-inducing pollens thrive on higher temperatures and CO2 concentrations, factors that will characterise the next decades. These results indicate that increasing pollen and longer seasons will increase the likelihood of seasonal allergies.

Health consequences of pollen allergies

Increasingly harsher pollen seasons are becoming more and more a threat to global public health. The World Health Organization estimates that allergic disorders will affect half of the planet’s population by 2050. Worldwide, allergies currently affect 10%-30% of the population and 40%-50% of children (American Academy of Allergy, Asthma & Immunology). 

The rise in pollen concentrations is not the only factor contributing to these increases. Indeed, the many ways the pollutants react with pollen definitely play a role in this. Pollutants’ chemicals destroy pollen’s cell walls, breaking the relatively large pollen grains into microparticles. These microparticles can enter the lungs deeper and become more dangerous for patients. In addition to this, pollutants can trigger an allergic reaction with a higher probability.

Improving the outlook

The aforementioned research is based on models relying on historical data. These models predict pollen emissions in response to several factors like temperature and precipitation for some common allergy-inducing plants. The process considers the atmospheric carbon dioxide increments and variations in plant distributions caused by climate change. While many airborne pollen-producing plants might thrive, others might not flourish as much in a warmer environment reach in CO2. Furthermore, the expansion of some plants might come at the expense of other allergen plants.

The models compared the amount of pollen released in two prospective long term climate scenarios. The first scenario was characterised by modest greenhouse gas emissions and the second one by CO2 higher than 2.5 times their current level. The latter resulted in a protracted and more intense pollen season. Instead, the more moderate scenario saw the pollen impacts decreasing by half compared to the previous one. This highlights how much tackling climate change will have critical benefits to our respiratory health.