Is the global rise of asthma an early impact of anthropogenic climate change?

Abstract

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.

Figure 1

Changes in asthma point prevalence observed since 1956. The locations used different diagnostic criteria, but these were consistent within each study location. Different studies for the same nation are distinguished by a, b, c, and d. Data from Pearce et al. (2000).

Figure 2

Three-monthly seasonal average atmospheric CO₂ concentration recorded at Mauna Loa Observatory, Hawaii, from March 1958 through December 2002 [data from Keeling and Whorf (2003)]. Highest CO₂ occurs in the northern hemisphere spring [March, April, May (MAM)]. Because this is peak growing season for northern hemisphere plants, the higher spring CO₂ levels may further magnify the impact on plant growth and pollen production. DJF, December, January, February; JJA, June, July, August; SON, September, October, November.

Figure 3

Percentage change in pollen quantities (Ambrosia artemisiifolia L.) produced under different concentrations of atmospheric CO₂. Increase in pollen quantity is shown for CO₂ concentrations equivalent to preindustrial levels (280 ppm), through 1950s levels, to 2000 levels and to potential future levels. ^aData from Ziska and Caulfield (2000). ^bData from Wayne et al. (2002).

Figure 4

Schematic diagram of the relationship between global climate change and the rise in asthma prevalence and severity, via impacts of climate change on plant and pollen attributes. ↑, increase.