Advances in Environmental and Engineering Research Climate Change, CO 2 -Concentration, and the Impact on Long-Term Pollen Observation with Implications for Human Health

Climate change has a major impact on nature and influences ecological systems. The increase in the CO 2 -concentration in the atmosphere is a major driver of global warming. This study showed that global warming has a major impact on the release of pollen, and hence, on the people suffering from allergies in Switzerland. Basel is a station where long-term pollen observation is conducted, and the data was used to investigate the change during the last 52 years. There are stations throughout the world to measure the atmospheric CO 2 concentration. Data from these stations showed an increase in temperature, which influences the biosphere. We found that the flowering time of Hazel, Birch, and Grass pollen has shifted forward in the corresponding season, inducing hay fever early in spring. Earlier pollen release is strongly correlated with and caused by an increase in temperature. This study showed the relationship between increasing CO 2 -concentration in the atmosphere, the increasing air temperature followed by increasing and earlier pollen counts, and finally, increasing prevalence of pollinosis over half a century.


Introduction
Climate change is a major threat to humans. The increase in atmospheric CO 2 concentration is the primary cause of climate change, as mentioned by Arrhenius [1]. However, the first political action against climate change was considerably delayed and was initiated with the establishment of the Intergovernmental Panel on Climate Change in 1988 [2].
Climate change severely affects very different social areas like agriculture, tourism, energy, and health [3]. A major problem regarding mitigation of climate change is the long-term effect that prevents major actions. This was realized during the corona pandemic when the threat of climate change was mostly neglected.
The consequences of increasing CO 2 -concentration in the atmosphere by traffic or heating are a large threat.
Health is one of the most important aspects to be strongly influenced by an increase in air temperature. The impacts of climate change on human health include heat-related mortality [4], the appearance of vector-borne (mosquito, sandfly, and tick) and rodent-borne infections in the higher latitudes and altitudes [5], and increasing cases of inflammatory bowel disease and infectious gastroenteritis in hospitals during heatwaves [6]. Finally, the rising air temperatures and carbon dioxide concentrations result in increased pollen production, allergenicity, and the advancement and lengthening of the pollen season in some plant species [7,8].
Several studies across Europe showed a positive or negative influence of meteorological variables on pollen count and pollen season [9][10][11].
Advancing and lengthening of the pollen season can only be seriously demonstrated by longterm pollen measurements. The pollen trap of Basel was the first one in Switzerland, and the technology has been unchanged for 52 years [12][13][14].
The objective of this study was to show the association between the increasing CO 2concentration in the atmosphere, the increasing air temperatures followed by increasing and earlier pollen counts, and the increasing prevalence of pollinosis in Switzerland.

CO 2 Data
The Schauinsland is a mountain in the Black Forest, 1,284 m above sea level. The measurement of CO 2 is operational since 1972 and operated by the German weather service, which is a part of the global atmosphere watch (GAW) of the World Meteorological Organization (WMO).
The Zugspitze at 2,962 m above sea level is the highest peak of the Wetterstein Mountains, as well as the highest mountain in Germany. There, the measurement of CO 2 is operational since 1995.
The Mauna Loa Observatory (MLO) is located on the north flank of Mauna Loa Volcano, on the big island of Hawaii, 3,397 m above sea level and operated by the National Oceanic and Atmospheric Administration (NOAA) since 1952.
The Jungfraujoch research station is situated 3,450 m above sea level, between the peaks of the Jungfrau (4,158 m a.s.l.) and the Mönch (4,099 m a.s.l.) and operated by the University of Bern.

Meteorological Data
Meteorological data were collected at the meteorological station of Basel-Binningen, 316 m above sea level. The air temperature was measured 2 m above the ground according to the recommendations of the World Meteorological Organization. The temperature at the climatological station in Basel was measured by the automatic monitoring network of the Federal Office of Meteorology and Climatology. The stations deliver a multitude of data on the weather and climate in Switzerland every ten minutes. The data is automatically transmitted to the central database, where various quality assurance checks are performed.

Pollen Data
Pollen data from Burkard Seven Day Recording Volumetric Pollen and Spore Trap Hirst [15], with a sucking rate of 10 l minute -1 , were available for 52 years for Basel . The pollen trap in Basel was located at the Kantonsspital building, 260 m above sea level. The distance between the pollen trap and the meteorological station was about 3 km.
The pollen amounts and the release of Corylus, Betula, and Poaceae were analyzed for 52 years (1969 to 2020). This was one of the longest time series in Europe [16].
The start of the pollen season was defined as the day when the sum of the daily counts reached 2.5% of the annual pollen count, and the end of the pollen season was the day when the sum of daily counts reached 97.5% of the annual pollen count, whereby, the pollen season encompassed 95% of the annual pollen recorded. Different durations have been used to define the start and length of the pollen season [17].
The data for Corylus between 1975 and 2019 were not available due to technical problems of the pollen trap in the corresponding years.

Epidemiological Data
The epidemiological data on the prevalence of pollinosis in Switzerland were used from previous studies [18,19]. Spring pollinosis is mainly induced by hazel and birch pollen in January/February for Hazel and in March for Birch. Summer pollinosis is mainly induced by grass pollen from May to July. Therefore, this study was focused on these three pollen taxa.

Statistical and Graphical Analyses
Statistical analysis (t-test, Pearson's correlation) and graphical representations were made in Microsoft Excel.

Results
An overview of the increase in atmospheric CO 2 -concentration is provided in (Figure 1). Data for Jungfraujoch was only available since 2010; therefore, the other three stations (Mauna Loa, Schauinsland, and Zugspitze) were included to incorporate the data since 1969 for the content of pollen and the incidence of pollinosis. Generally, all four stations showed a similar increase in CO 2concentration and explained the observed increase in temperature ( Figure 2).  The increase in the annual mean temperature in Basel-Binningen from 1969 to 2020 is shown in Figure 2. The increase in temperature might partly be due to the urban heat island effect [20].
An overview of the increase in Corylus pollen from 1969 to 2020 is shown in Figure 3. The linear trend indicated an increase from approximately 750 annual pollen counts to approximately 2,000 annual pollen counts. The correlation between air temperature and the annual pollen count of Corylus in Basel is shown in Figure 4.

Figure 4
The correlation between the annual mean temperature and the annual pollen count of Corylus from 1969 to 2020 in Basel.
Pearson's correlation coefficient for the correlation between the annual mean temperature and the annual pollen count was 0.56, indicating a strong and statistically significant correlation (p < 0.05) as shown in Table 1. The increase in the annual Betula pollen count from 1969 to 2020 is shown in Figure 5. The linear trend indicated an increase in the annual pollen count from 5,500 to 6,500 (approximately).  An overview and the statistical analysis of the correlation between the annual mean temperature and the number of days since the beginning of Betula pollen released from 1969 to 2020 in Basel are presented in Figure 7 and Table 2. Pearson's correlation coefficient was -0.49, and the correlation was significant (p < 0.05). The correlation suggested that flowering is directly enforced by the rise in temperature [21,22].

Figure 7
The correlation between the annual mean temperature and the number of days since the beginning of Betula pollen release from 1969 to 2020 in Basel.  (Figure 8). This represented a shift of approximately eight days in 52 years. The overview and the statistical analysis of the correlation between the annual mean temperature and the number of days since the beginning of Poaceae pollen release from 1969 to 2020 in Basel are shown in Figure 9 and Table 3. Pearson's correlation coefficient was -0.51 and was statistically significant (p < 0.05). The correlation suggested that flowering is directly enforced by an increase in temperature.

Figure 9
The correlation between the annual mean temperature and the number of days since the beginning of Poaceae pollen release from 1969 to 2020 in Basel. For the results of previous studies (Figure 10), the prevalence of pollinosis is shown in the same time frame as the increase in CO 2 -concentration and the increase in temperature and the release of pollen.

Discussion
The concentration of CO 2 is a major source of global warming, as mentioned by Arrhenius in 1910. Systematic measurements of CO 2 -concentration in the atmosphere started in Mauna Loa, Hawaii, in 1952 [23]. The increase in CO 2 from around 320 ppmV in 1969 to around 420 ppmV in 2020 demonstrated the situation worldwide, as well as in Switzerland, and also explained the observed temperature increase in Basel-Binningen.
The phenology of Betula showed the heating and chilling requirements that are needed to trigger bud development and to assess how global climate change might influence phenology in this species [24].
Several climate-related parameters, including photoperiod, water availability, temperature, and wind speed and direction, affect plant phenology. In annual grasses, the key factor is the weather that prevails during the growing season [25].
The increase in temperature in Basel-Binningen ( Figure 2) is the reason for the earlier flowering of trees and herbs like Corylus, Betula, and Poaceae. Earlier flowering and the corresponding pollen release cause hay fever symptoms, starting in January for Corylus and in March for Betula. These findings are similar to those reported from several European countries [26,27]; thus, indicating the relevance of climate change and its impact on allergy.
Global warming, caused by increasing atmospheric CO 2 concentrations by traffic and heating, has caused earlier flowering and pollen release in plants and thus, affected human health by increasing the instances of allergy and asthma.
Global change impacts agriculture, tourism, assurance, migration, and human health. The effects on human health are very diverse and include aspects like heat-related mortality, vector-borne infections, and an increase in the cases of inflammatory bowel disease and infectious gastroenteritis in hospitals during heatwaves [28].
The epidemiological situation indicated a direct link between increasing CO 2 -concentration in the atmosphere; thus, inducing an increase in the air temperature. This, in turn, promotes earlier flowering and increases pollen counts due to the higher availability of CO 2 in the air that has a fertilizing effect. The increasing prevalence of pollinosis might also have additional causes, such as the 'western style of life' (e.g., junk food consumption or increased hygiene requirements) [29,30].
To cope with these impacts on human health, the only approach is to stabilize and later decrease the CO 2 concentrations in the atmosphere either by reducing anthropogenic emissions or by implementing technical measures to decarbonize the atmosphere.

Conclusions
The increase in CO 2 -concentration in the atmosphere is a major driver of global warming. Global warming is the cause for the earlier flowering of plants like Betula or Poaceae that might be responsible for allergy and asthma. Moreover, the incidence of pollinosis is also increasing. Reducing the CO 2 -concentration in the atmosphere is the only strategy to cope with global warming and its negative impacts, as proposed in the Paris agreement in 2015 [31].