Is the Global Rise of Asthma an Early Impact of Anthropogenic Climate Change?

Article excerpt

The increase in asthma incidence, prevalence, and morbidity over recent decades presents a significant challenge to public health. Pollen is an important trigger of some types of asthma, and both pollen quantity and season depend on climatic and meteorologic variables. Over the same period as the global rise in asthma, there have been considerable increases in atmospheric carbon dioxide concentration and global average surface temperature. We hypothesize anthropogenic climate change as a plausible contributor to the rise in asthma. Greater concentrations of carbon dioxide and higher temperatures may increase pollen quantity and induce longer pollen seasons. Pollen allergenicity can also increase as a result of these changes in climate. Exposure in early life to a more allergenic environment may also provoke the development of other atopic conditions, such as eczema and allergic rhinitis. Although the etiology of asthma is complex, the recent global rise in asthma could be an early health effect of anthropogenic climate change. Key words: aeroallergens, anthropogenic climate change, asthma, carbon dioxide, phenology, pollen, temperature. doi:10.1289/ehp.7724 available via [Online 20 April 2005]


Global Trends in Asthma

Although asthma patterns vary throughout the world, considerable increases in both the prevalence of asthma and its severity have occurred globally over recent decades (Bach 2002; Isolauri et al. 2004; Pearce et al. 2000). Because this rise has been far too rapid to implicate any genetic basis for change, various environmental factors and lifestyle factors have been proposed, and most recently the "hygiene hypothesis" has been explored extensively (Bach 2002) as an explanation for increased asthma prevalence. In this commentary, we propose an additional explanation: that a significant proportion of the increase in both asthma prevalence and its severity is the result of anthropogenic climate change.

Evidence for the global increase in the burden of asthma has come from studies of incidence, prevalence, and morbidity. Asthma prevalence appears to have increased since the early 1960s (Beasley 2002), with the rise in asthma prevalence occurring among both children and adults (Beasley et al. 2000) and in a wide range of countries with differing lifestyles (Beasley 2002). Over a similar period, the prevalence of other atopic disorders, such as allergic rhinitis, atopic eczema, and urticaria, has also increased, once again throughout the world (Bach 2002; Beasley 2002). Figure 1 shows increasing prevalence of asthma in several locations. Although different diagnostic definitions have been used in different locations, each location shown is internally consistent, and each shows an increase in asthma prevalence.


Studies of hospital admissions and surveys of symptoms of severe asthma indicate increased asthma morbidity since the early 1960s (Beasley 2002; Kao et al. 2001; Kerr 2002), particularly in young children (Beasley 2002). This increase in asthma morbidity can not be completely explained by an increase in readmissions, diagnostic transfer from related disease categories, or changes in medical practice (Beasley 2002).

In contrast with the overall trend of a rise in asthma over several decades, a few studies have reported an apparent leveling off or even a decline of asthma in recent years. Robertson et al. (2004) reported a 26% decline in the prevalence of reported wheeze between surveys conducted in 1993 and 2002 in Melbourne, Australia, among children 6-7 years of age. The study also found a reduction in emergency department visits and hospital admissions, which may be due at least partly to improved asthma management. Interestingly, the same survey found a 31% increase in allergic rhinitis, which is commonly linked to asthma, a 55% increase in eczema, and an increase in those taking regular steroid medication among those with frequent wheeze. …