How does the climate crisis affect the lungs?

The climate crisis has undoubtedly reached Europe and Switzerland, not to say taken hold of them. According to the German Weather Service (DWD), the past summer of 2022 was the warmest ever recorded since 1951, and the EU climate change service Copernicus confirms this for Europe: compared to the long-term average from 1991 to 2020, the period from June to August was 1.34 degrees warmer.

The southwest of the continent was particularly affected [1]. The heat waves have led to massive drought in agriculture in many places, resulting in crop losses. They have caused forest fires on more than 750,000 hectares of land. In the process, the EU and the UK emitted 6.4 million tons of carbon – the most in 15 years [2]. The lack of rain has led to low water levels, if not drought, in inland lakes, reservoirs and, of course, rivers. The rapid melting of glaciers in the Alps has not been able to change this much, especially since they will no longer exist in a few years (or decades) anyway [3].

Compared to the 1960 birth cohort – most of whom experienced this summer of heat – lifetime exposure to extreme events for those born in 2020 will change as follows, according to the Paris Climate Agreement estimates: nearly 6.8 times as many heat waves, 2.6 times as many droughts and crop failures, and 2 times more frequent wildfires [4].

This sets the dramatic framework in which the health effects on us humans have been studied so far and will need to be further analyzed in the future. This article is primarily concerned with the pulmonary consequences known to date. Of course, there are considerable intersections with some air pollutants that have essentially been and continue to be created by the combustion of fossil fuels and have thus caused the greenhouse effect with its consequences in the first place. Due to the brevity, the explanations can only be “striking”.

Which air pollutants are significant?

Fine dusts, especially PM 2.5, i.e. with a diameter of up to 2.5 µm and smaller, consist of different components such as inorganic fractions (e.g. ammonium sulfates and nitrates, hydrochloric acid), elemental soot, metals, soil or dust particles, furthermore organic chemicals such as urea ammonia (NH3) from liquid manure or acids (e.g. sulfuric acid) and biological materials (e.g. pollen, fungal spores). Due to their small size they are respirable, i.e. they are inhaled into the bronchioli, the ultrafine particles (UFP) <0.2 µm also penetrate the alveolar-capillary barrier and are thus systemically relevant.

Pulmonary pathophysiology is explained in part by bronchial mucosal inflammation due to increased activation of basophil and eosinophil granulocytes. As a result, a hyperirritable bronchial system may develop, allowing other asthmatic trigger factors such as infections, physical stress, or even psychological stress to take effect. In addition, the Th2 immune response can be activated, thereby promoting sensitization as a prerequisite for a possible subsequent allergy. Furthermore, particulate matter – especially UFP – and ozone cause oxidative stress at the lung, which negatively affects lung growth and thus lung function, and also promotes infections of the deep respiratory tract [5].

In a recent epidemiologic study presented at ESMO involving more than 400,000 patients in England, South Korea, and Taiwan, air pollution with PM 2.5 was identified as a major promoter of mutations in the EGFR gene. Although this mutation also occurs in normal aging, it remains inactive, but can cause lung carcinoma if PM-2.5 persists. This is explained by an excessive inflammation of mutation-affected cells. This EGFR mutation was also found in 18% of 250 lung-healthy people who were kidney smokers and lived in clean-air zones, but it remained inactive here as well. In animal experiments with mice, it was also demonstrated that the proinflammatory messenger interleukin-1 could be blocked by an antibody, so that lung carcinomas were prevented [6].

According to the Global Climate Health Alliance (GCHA), smoke plumes from wildfires contain a complex mixture of gaseous particulate matter consisting of carbon monoxide (CO), polycyclic aromatic hydrocarbons (PAHs), and soot particles. Depending on the thermals and prevailing winds, these are transported over thousands of kilometers and can acutely trigger coughing, shortness of breath, and in predisposed individuals, asthma attacks [7]. However, the air pollutants from wildfires identified to date are also significant for long-term, health effects such as carcinogenesis.

Ground-level ozone and nitrogen oxides

Ozone (_O3), in combination with nitrogen oxides (_NO/NO2), is one of the most important air pollutants relevant to health. Thus, prolonged sunshine and hot spells can worsen asthma symptoms in all age groups. This is because UV radiation causes a significant increase in ozone concentration when nitrogen oxides (_NO/NO2) are present at the same time. Above all, _NO2 comes from traffic-related emissions, the source of which is fossil energy (gasoline, diesel) powered vehicles. UV radiation splits _NO2 into nitric oxide (NO) + an oxygen radical. The O radical combines rapidly with oxygen (_O2) to form _O3. In summer, ozone is therefore mainly produced in cities with a lot of traffic and is blown from there by air currents, possibly plus wind, into the rural environment. During evening rush hour traffic in the city, ozone is then reduced again with NO, which is also “provided” by traffic, to _NO2 and _O2. Since there is less traffic in rural areas, there is a lack of NO to break down ozone back to oxygen and _NO2. This explains the apparent paradox that average ozone concentrations in rural areas of Germany, 57 µg/m³, have been significantly higher than those in urban areas, 42 µg/m³, for more than 30 years.

The target value for the protection of human health has so far been 120 µg/m³ _O3 in the so-called 8-hour average in the EU, and 100 µg/m³ _O3 according to the WHO. Short-term ozone concentrations above 120 µg/m³ may cause acute respiratory problems, as _O3 is a reactive irritant gas that penetrates deep into the airways and causes acute mucous membrane irritation or inflammation. The so-called oxidative stress is accompanied by cough, chest tightness and shortness of breath, thus leading to acute asthma attacks [8].

Permanent ozone exposure, even below 120 µg/m³, leads to reduced lung growth in children up to puberty [9], and in adolescents and adults lung function is impaired and the elastic connective tissue of the lung is chronically damaged. This increases mortality from respiratory diseases in adults.

Thunderstorm asthma and pollen exposure

This phenomenon has been known for some years, especially in Australia, as “thunderstorm asthma” [10], but beyond casuistry it will also increase in Southern and Central Europe. Physically, heat causes increased regional evaporation and thus water contamination of the atmosphere, which is then discharged elsewhere by thunderstorms as so-called heavy weather events with sometimes massive downpours. In the so-called thunderstorm asthma, pollen increasingly breaks out 1-2 hours before the onset of the thunderstorm due to the “osmotic shock”. This refers to heat, electrostatic charge from lightning and high humidity. The allergens contained in pollen bind to fine dusts, which are inhaled as far as the bronchioli, as explained. Particularly affected are adolescents and young adults with a hyperreactive bronchial system, who usually have only mild asthma symptoms so far, e.g., on exertion, and therefore rarely have continuous therapy; furthermore, they usually do not carry an emergency antiasthmatic spray. This is reinforced by the fact that the increase in the greenhouse gas_CO2 also leads to increased pollen and flower production, as can be shown using ragweed as an example [11].

Conclusion

The climate crisis has arrived in Switzerland with heat, drought and severe weather events (Fig. 1), moreover, flood disasters are increasing in Central Europe, such as in the Ahr Valley in Germany in 2021. Even if warming were to be halted, it will be with the next generations for life and will affect their health. Focusing on the lungs, the air pollutants particulate matter, ozone, and nitrogen oxides will be discussed and their pathophysiology will also be presented in combination with pollen counts. Attention is drawn to the growing importance of thunderstorm asthma in adolescents and young adults.

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