Educational aims
The reader will be able to:
- •
Explain how children are more vulnerable than adults to the respiratory health effects of climate change due to physiological and behavioural factors.
- •
Describe the mechanisms by which climate change, through increasing temperatures, allergens, mold, air pollution, and extreme weather events, can negatively impact respiratory health in children.
- •
Discuss the observed and projected effects of climate change on asthma, respiratory infections, lung development and lung function in children.
- •
Outline mitigation and adaptation strategies that healthcare professionals and society can implement to protect children’s respiratory health in the context of climate change.
Abstract
Climate change has significant consequences for children’s respiratory health. Rising temperatures and extreme weather events increase children’s exposure to allergens, mould, and air pollutants. Children are particularly vulnerable to these airborne particles due to their higher ventilation per unit of body weight, more frequent mouth breathing, and outdoor activities. Children with asthma and cystic fibrosis are at particularly high risk, with increased risks of exacerbation, but the effects of climate change could also be observed in the general population, with a risk of impaired lung development and growth. Mitigation measures, including reducing greenhouse gas emissions by healthcare professionals and healthcare systems, and adaptation measures, such as limiting outdoor activities during pollution peaks, are essential to preserve children’s respiratory health. The mobilisation of society as a whole, including paediatricians, is crucial to limit the impact of climate change on children’s respiratory health.
Global warming corresponds to the rapid increase in the average temperature of the Earth’s surface during the 20th and 21st centuries, and climate change more broadly refers to the resulting modification of large-scale weather patterns . Global warming is a consequence of human activities, mainly via the emission of greenhouse gases (GHGs) such as carbon dioxide (CO2). Currently, the CO2 content of the atmosphere is increasing and, as a result, the planetary temperature is also rising. The average planetary temperature of the decade 2011–2020 was 1.09 °C higher than during the reference period 1850–1900, and each of the last four decades has been warmer than the previous one . Children are vulnerable to the consequences of climate change, particularly their respiratory system which is in direct contact with the atmosphere. The objective of this review is to describe the links between climate change, its impacts on the atmosphere, and the observed and expected consequences of these changes on children’s respiratory health.
From global warming to climate change
Global warming has a number of consequences for the climate. Firstly, it is accompanied by an increase in the frequency, duration and intensity of extreme temperature events, whether cold spells during the winter due to disturbances in the polar vortex , or extreme heat events . Extreme heat events increase the risk of drought, as was the case in the summer of 2022, when a heat wave caused an unprecedented drought in western France, northern Italy, Spain, and Portugal . A vicious cycle then set in, with the soil becoming increasingly dry due to high temperatures and lack of precipitation, which in turn contributed to further temperature increases. An associated risk with these episodes is wildfires. Between 1979 and 2013, the length of meteorological fire seasons increased by 19 % globally . In California, the area of forest burned increased fivefold between the summers of 1996–2021 and the summers of 1971–1995 . In Europe, projections anticipate a tenfold increase in the risk of catastrophic wildfires in Southern Europe if the intermediate climate projection scenario (SSP2-4.5) occurs, i.e., global warming of 2 °C in the short term .
Climate change also leads to an increase in the frequency and intensity of rainfall, thunderstorms, storms, and cyclones, and thus flooding. On a global scale, an increase in precipitation has been observed in nearly two-thirds of the 8,326 stations included in a study, correlated with the increase in planetary temperature . Projections also indicate an increase in the frequency of severe storms, both in the United States and in Europe, with a growing probability of atmospheric conditions contributing to lightning, hail, and wind gusts . In tropical zones, the trend is towards an increase in the frequency and intensity of cyclones since 1970 . All of these phenomena have led to an increase in the frequency and intensity of flooding since the 2000 s . Between the expansion of flood-prone areas and population growth, one study estimated that an additional 58 to 86 million people were exposed to flooding in 2015 compared to the year 2000, representing a 20 to 24 % increase in the global population exposed to flooding . The effects of climate change are therefore already being felt.
Children: a vulnerable population
Children are the first victims of climate change. Increasing temperatures expose them to infectious diseases such as malaria or dengue fever, periods of drought to malnutrition, periods of heavy rainfall and flooding to drowning and acute diarrhoea epidemics, and the proliferation of these extreme weather events to a deterioration in their mental health .
Their respiratory system is particularly vulnerable to the consequences of climate change ( Fig. 1 ). Compared to adults, children are more exposed to airborne particles such as pollutants, allergens, moulds, and infectious agents. Their ventilation per unit of body weight is higher than that of adults in order to meet the increased production of CO2 due to their growth, the increase in their body surface area relative to their weight, and the relatively larger size of the most active organs such as the brain . To eliminate this CO2, the respiratory rate increases in children, exposing them further to airborne particles . Children also breathe more frequently through the mouth because of their greater nasal resistance, which promotes pulmonary deposition of particles . Finally, children spend more time being active, which increases both their ventilation and mouth breathing, and more time being active outdoors, further aggravating the exposure of their respiratory system to airborne particles . Another non-physiological factor is that infants and young children breathe at a lower height from their strollers or due to their small size, and are therefore more exposed to atmospheric pollutants that are heavier than air .
Children are therefore more exposed to airborne particles than adults, which is all the more problematic as the consequences of harmful environmental exposures are more severe in children than in adults. The respiratory system of children in the first year of life is indeed more vulnerable to environmental factors due to the small diameter of the airways, particularly the bronchioles, with a higher risk of obstruction and respiratory distress . But the main consequence is long-term: environmental exposures that occur in childhood can have consequences for the individual’s entire life. Indeed, lung development, initiated from the first weeks of pregnancy, continues for about two years after birth, while lung growth continues until around the age of 20, with lung function reaching its peak at this age before gradually declining . Any impairment of lung function in childhood will therefore have consequences on lung function in adulthood, which is itself a major determinant of chronic respiratory pathologies such as chronic obstructive pulmonary disease but also of all-cause mortality . Environmental exposures related to climate change on the child’s respiratory system will therefore likely have consequences for the rest of their lives .
Global warming and respiratory infections in children
Respiratory infections represent the second leading cause of mortality in children worldwide after complications of prematurity, responsible for more than 900,000 deaths per year in children under 5 years of age . They also have a long-term impact, as it has recently been shown that a respiratory infection in early childhood was associated with a doubled risk of premature death (before 73 years of age) in adulthood, even after adjusting for the child’s socioeconomic status, the number of people in the household during childhood, birth weight, sex, and smoking in adulthood .
In temperate climates, most viral infections occur in autumn and winter when temperatures are low, it would be intuitive to think that the increase in temperatures would allow for a decrease in respiratory infections. However, several factors contribute to respiratory epidemics, such as the behaviour of the population (number of contacts, in confined spaces or not), which complicates the analysis of the isolated effect of an increase in temperature. Epidemiological data show overall stable rates of hospitalizations for respiratory syncytial virus (RSV) bronchiolitis in Europe before the SARS-CoV-2 pandemic , while global warming continued. Should future research confirm an association between warmer-than-average winter temperatures and reduced incidence of RSV bronchiolitis and influenza epidemics , the long-term implications of this potential change remain uncertain. The reduced population immunity to these viruses resulting from milder epidemic seasons could potentially lead to the emergence of earlier and more severe outbreaks in subsequent years .
It is also difficult to predict the evolution of the risk of bacterial respiratory infections. Streptococcus pneumoniae pneumonias are favoured by a cold and dry climate, but also by the viral respiratory infections whose uncertain evolution we have discussed . The influence of environmental factors on Mycoplasma pneumoniae pneumonias has been much less studied. A single study conducted in Japan and including data from 12,000 children found an increase in the number of cases between 1999 and 2007, and a 16.9 % increase in the weekly number of cases per 1 °C increase in average temperature . In Europe, no increase in the number of cases was found between 2011 and 2016 for these Mycoplasma pneumoniae pneumonias, which occur in epidemics every 4 to 7 years . Finally, in patients with cystic fibrosis, a warmer ambient temperature was associated with more frequent Pseudomonas aeruginosa colonisation .
Overall, the evolution of respiratory virus epidemics and pneumococcal or mycoplasma pneumonias remains very uncertain in the context of climate change. New therapeutics such as anti-RSV monoclonal antibodies should have a much greater effect on viral and bacterial ecology than climate change, except in the event of the emergence of a new infectious agent as was the case for SARS-CoV-2.
Heat waves, cold waves, and respiratory health in children
The respiratory system is sensitive to extreme temperatures. Exposure to cold, dry air or, conversely, to hot air can lead to bronchoconstriction, although the mechanisms underlying these reactions are not fully understood. The main hypothesis during exposure to cold, dry air is dehydration of the airway surface liquid, leading to secondary release of pro-inflammatory mediators and bronchoconstriction . During exposure to very hot (49 °C) and humid air, the C nerve fibres of the bronchial epithelium seem to be involved in the induced cough and bronchoconstriction, notably via their transient receptor potential vanilloid 1 (TRPV1) receptors .
Regardless of the mechanisms involved, epidemiological studies confirm the vulnerability of the respiratory system to extreme temperatures, with an increase in asthma exacerbations and emergency department visits in both cases. A recent meta -analysis combining studies conducted in adults and children found an increase in the relative risk of asthma exacerbation in cases of extreme heat and extreme cold of 1.07 (95 % CI: 1.03–1.12) and 1.20 (95 % CI: 1.12–1.29), respectively . An epidemiological study conducted in China since then confirms these results with an increase in the risk of emergency department visits secondary to extreme temperatures (above 30 °C – 90th percentile and below 14.2 °C – 10th percentile), more pronounced in male patients and children . These findings are also consistent with an Australian study that reported increased emergency department visits for asthma exacerbations during both extreme heat (above 26.5 °C – 95th percentile) and cold events (below 13.8 °C – 5th percentile) .
The impact of extreme temperatures extends beyond children with asthma, potentially altering normal lung development. A French cohort study of 343 mother–child pairs showed that exposure of mothers and newborns to heat and cold waves was significantly associated with a decreased functional residual capacity and an increased respiratory rate in female newborns .
In summary, the deleterious impact of temperature on the respiratory system follows a U-shaped curve with maximal impact in cases of cold spells and heat waves.
Climate change, allergens, and respiratory health
Climate change also leads to an increase in pollen concentrations and an extension of pollen seasons. A retrospective study that analysed pollen data from 17 locations in the northern hemisphere found an increase in pollen concentrations in 12 of these 17 locations, correlated with the increase in temperature . The same study showed a lengthening of pollen seasons in 11 of the 17 locations, by an average of 0.9 days per year, again correlated with the increase in temperatures. Two subsequently published studies, conducted in South Korea and North America on data covering the last 20 and 30 years respectively, confirm these results, with a correlation between the increase in temperatures and the increase in pollen concentration and/or the duration of the pollen season . This increase in pollen exposure is associated with an increase in the number of children sensitised to pollen and greater morbidity in children with asthma. A study conducted over 22 years on 8,295 children in the Seoul metropolitan area (South Korea) showed a correlation between the increase in the duration of pollen seasons, from 98 to 140 days per year between 1998 and 2019, and the increase in children’s sensitisation to tree pollen (+0.28 % per year) . In children with asthma, greater exposure to pollen increases the risk of asthma exacerbations requiring emergency department visits. A systematic literature review that included 14 studies, 3 of which could be meta -analysed, found an increase in the average number of paediatric emergency department visits for asthma of 1.88 % (95 % CI 0.94 %-2.82 %) per 10 grains of grass pollen/m3 increase in exposure, up to three days after exposure . Projections in the United States suggest an 8 % increase in emergency department visits in the case of a moderate increase in GHGs and a 14 % increase in the case of a significant increase in GHGs by 2090 due to greater exposure to oak, birch, and grass pollen . Similarly, a systematic literature review with meta -analysis (n = 12 studies) found an increase in hospitalisations for asthma exacerbations during exposure to birch and grass pollen (although only significant in the meta -analysis of case-control studies in the latter case), with a higher risk in 2–12-year-olds compared to 13–18-year-old adolescents . An Australian study finally observed a significantly increased risk of rehospitalisation during the grass pollen season, particularly in 2–12-year-olds . Part of these asthma exacerbations could be explained by an increased susceptibility of allergic children to viral infections. Allergic sensitisation has indeed been associated with an impaired immune response to rhinovirus infection in bronchial epithelial cells of atopic children, with or without manifestation of asthma . These results have been confirmed by studies showing that anti-allergic therapies, such as allergen immunotherapy or administration of anti-IgE biotherapy (omalizumab), can increase interferon production and reduce the risk of asthma exacerbations in asthmatic patients .
In summary, the increased exposure to allergens due to climate change could degrade the quality of life of children with asthma and increase their use of healthcare services.
| Thunderstorm asthma |
|---|
| Climate change is causing an increase in extreme events such as thunderstorms, which can trigger sudden epidemics of asthma exacerbations, a phenomenon called “thunderstorm asthma”. Thunderstorm asthma requires a very high concentration of pollen in the air (>100 grains/m3), a humidity level above 70 %, precipitation, and wind gusts. The numerous pollen grains are then broken by osmotic shock upon contact with rainwater, each releasing around 700 granules small enough to quickly and deeply penetrate the airways. The most emblematic case of thunderstorm asthma occurred in Melbourne, Australia in 2016. In the 30 h following the storm on November 21, an additional 3,365 emergency department visits and 476 hospitalisations were recorded for asthma compared to usual figures. Male children and adolescents were the most affected by the phenomenon . |
Climate Change, Mould, and children’s respiratory health
Climate change, by increasing precipitation, storms, and hurricanes, raises the degree of humidity inside and outside buildings, leading to the development of mould . The successive hurricanes Katrina and Rita in the Gulf of Mexico illustrate the impact of these phenomena on the risk of mould exposure: after 80 % of New Orleans was flooded for more than six weeks, over 100,000 homes experienced significant mould growth . Moreover, experimental studies have found an increase in the production of mould spores such as Alternaria alternata when CO2 concentrations were increased .
The links between mould and asthma have been the most studied. Exposure to moisture and mould is associated with an increased risk of developing asthma, whether at preschool age, school age, or adolescence . For instance, in a cohort of 3,798 Swedish children, exposure to moisture and mould at 2 months of age was associated with an odds ratio of 1.73 (95 % CI: 1.20–2.50) of developing secondary persistent asthma up to 16 years of age . Once asthma is diagnosed, exposure to mould has been associated with increased symptoms, asthma exacerbations , emergency department visits , and hospitalisations for asthma . Children with asthma sensitised to mould have decreased lung function and greater bronchial hyperreactivity compared to children who are not sensitised or are sensitised to other aeroallergens . They also have more severe and difficult-to-treat asthma due to lung inflammation dependent on interleukin-33, which is relatively resistant to inhaled corticosteroids . Finally, they may be more frequently subject to fatal asthma attacks . In other respiratory diseases, only one study has assessed mould exposure in patients with cystic fibrosis. Exposure to higher concentrations of Aspergillus fumigatus was associated with a higher risk of allergic bronchopulmonary aspergillosis, and its associated lung damage .
In summary, climate change could lead to asthma that is more severe and more difficult to treat as a result of increased precipitation, humidity and mould in certain regions of the world.
Climate Change, air Pollution, and children’s respiratory health
Air pollution depends on two factors: pollutant emissions and meteorological conditions. By modifying meteorological conditions, climate change has an effect on air pollution, particularly on concentrations of ozone and fine particulate matter (PM2.5), which are the most concerning pollutants for children’s respiratory health .
Ozone is a gas resulting from the physicochemical degradation of volatile organic compounds in the presence of sunlight and nitrogen oxides. PM2.5 refers to suspended particles with a diameter of less than 2.5 µm, which mainly emanate from wood heating, road traffic, construction sites, or chemical reactions between precursor gases present in the atmosphere.
Climate change influences ozone and PM2.5 concentrations in several ways. First, global warming increases ozone production via an increase in biogenic volatile organic compound emissions and an acceleration of the chemical reactions involved in its production . Ozone concentrations are thus higher during heat waves and in summer compared to winter in the northern hemisphere. Second, during periods of drought, the decrease in precipitation no longer allows the washout of suspended PM2.5, again leading to an increase in their concentration in the atmosphere . Climate change also favours episodes of air stagnation, particularly in tropical and subtropical zones , resulting in an accumulation of ozone and PM2.5. Finally, the increase in wildfires causes the emission of major quantities of PM2.5 that spread over a large scale. The wildfires in California in 2020 and 2021 thus produced some of the highest amounts of PM2.5 ever observed at monitoring stations, sometimes for weeks .
Ozone and PM2.5 aggravate the natural history of certain chronic lung diseases but also impair the respiratory health of children without lung disease. In children with asthma, exposure to ozone and PM2.5 is associated with an increase in respiratory symptoms , emergency department visits , and hospitalisations for asthma exacerbations . A study conducted in New York City based on 76,000 hospitalisations for asthma identified that the most vulnerable population on days of high pollution corresponded to children aged 6 to 18 years, with a 19 % and 20 % increase in hospitalisations for each 22 ppb increase in ozone and 12 μg/m3 increase in PM2.5, respectively . PM2.5 from wildfires has a particular harmfulness, with a risk of emergency department visits for respiratory symptoms 10 times higher than that observed for PM2.5 not coming from wildfires .
In children with cystic fibrosis, exposure to ozone and PM2.5 is associated with an increase in respiratory exacerbations . Exposure to PM2.5 has also been associated in these children with earlier Pseudomonas aeruginosa infection and a decrease in FEV1 .
In children in the general population, exposure to ozone and PM2.5 are risk factors for developing respiratory diseases. Children exposed to these pollutants, particularly those who engage in outdoor sports activities, are at higher risk of developing asthma . They are also at higher risk of pneumonia. A systematic literature review with meta -analysis published in 2017 found an increase in the risk of pneumonia of 1.7 % (95 % CI: 0.6–––2.4) per 10 µg/m3 of additional ozone concentration (16 studies included) and 1.8 % (95 % CI: 0.5–––3.1) per 10 µg/m3 of additional PM2.5 concentration (13 studies included) . Since its publication, a cohort study of 112,567 children under 2 years of age and 17,828 children aged 3 to 17 years in the United States confirmed this result, with a 15 % increase in the risk of lower respiratory infection in children under 2 years and a 32 % increase in children aged 3–17 years for each additional 10 μg/m3 of PM2.5 concentration. Exposure to PM2.5 was associated with an increased risk of RSV bronchiolitis in children under 2 years and influenza in children aged 3–17 years .
Ozone and PM2.5 also have effects on children’s lung function. Prenatal exposure to ozone and/or PM2.5 is associated with an increased risk of prematurity and intrauterine growth restriction , each of which are risk factors for respiratory morbidity and long-term decreased respiratory function . The impact of these pollutants on lung development and growth continues postnatally, with children born prematurely and exposed to PM2.5 having decreased lung volume between 7 and 12 years of age , and all children exposed to ozone and/or PM2.5 having decreased respiratory function between the ages of 18 and 24 years, i.e., at their peak respiratory function .
In summary, for the same level of emission by human activities, meteorological conditions aggravate exposure to ozone, and possibly to PM2.5, although this is more debated , with these two pollutants being responsible for high respiratory morbidity.
Climate Change, Pollen-Pollution Interactions, and children’s respiratory health
There is evidence for a deleterious effect of the association between exposure to pollution and pollen on respiratory health. Air pollution increases pollen production, enhances their allergenic potential, and facilitates their transport into the airways, their penetration through the damaged epithelium, and thus sensitisation or allergic reaction . Several experimental studies conducted in asthmatic adults have shown that exposure to ozone for several hours increased bronchial reactivity during an allergen challenge test , meaning that bronchoconstriction was induced by lower doses of allergens. An epidemiological study conducted in the Brussels region found this synergistic effect between exposure to ozone and birch pollen on the risk of hospitalisations for asthma, both in children and adults , and a paediatric study conducted in the Paris region also found an interaction between ozone concentration and pollen concentration on the risk of asthma exacerbations reported by parents . Regarding the interaction between PM2.5 and pollen, the results are more mixed: a study conducted in Canada found a synergistic effect between these two exposures on the risk of hospitalisations for asthma, both in children and adults , but these results were not confirmed in a paediatric study conducted in the United States .
Preserving children’s respiratory health in the era of global warming
Two types of measures should be considered to preserve children’s respiratory health from the consequences of climate change: mitigation measures and adaptation measures ( Fig. 2 ).
