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March 5, 2014

Climate Change Effects on Allergy


I am an allergist in a small community and I have been invited to be part of a panel on a TV current events program to discuss the effects of climate change on allergy in the community. I am aware of some data on the earlier start and prolonged nature of seasonal pollens. Is there good evidence of other changes we can expect?


By Dr. Gennaro D’Amato

Climate change and Allergic Respiratory Diseases

Global temperature has risen markedly over the last 30 years due to increases in greenhouse gas emissions, largely from anthropogenic sources. For example, mean annual central England temperatures have continued to rise and are now over 2° C higher than in the coldest period of the “Little Ice Age” in the late 17th century with half of this increase occurring in the last 40 years. The increase in temperature has also seen a rapid rise in the number of hot days and severe meteorological events such as the 2003, 2012 and 2013  heat wave where temperatures of 35°C and greater were reached resulting in around forty thousand excess deaths across Europe

It is now widely accepted that the earth’s temperature is increasing, as confirmed by warming of the oceans, rising sea levels, glaciers melting, sea ice retreating in the Arctic and diminished snow cover in the Northern Hemisphere. Moreover, changes are also occurring in the amount, intensity, frequency and type of precipitation as well as the increased of extreme events, like heat waves, droughts, floods and hurricanes. As stated in the recent Working Group I Report of the Intergovernmental Panel on Climate Change (IPCC) "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations"

The key determinants of greenhouse gas emissions are energy production, consumption and efficiency, transport, agriculture and food production and waste management and attempts at mitigating climate change will need to address each of these. However, while there is some uncertainty about predicting future meteorological trends, whatever interventions may be put in place to ameliorate climate change, it is likely that the world will experience more hot days, fewer frost days, and more periods of heavy rain and consequent flooding. Paradoxically it is likely that there will be more periods of drought. A body of evidence suggests that major changes involving the atmosphere and the climate, including global warming induced by human activity, have impact on the biosphere and human environment. Studies on the effects of climate changes on respiratory allergy are still lacking and current knowledge is provided by epidemiological and experimental studies on the relationship between asthma and environmental factors, like meteorological variables, airborne allergens and air pollution. However, there is also considerable evidence that subjects affected by asthma are at increased risk of developing obstructive airway exacerbations with exposure to gaseous and particulate components of air pollution. It is not easy to evaluate the impact of climate changes and air pollution on the prevalence of asthma in general and on the timing of asthma exacerbations. However, the global rise in asthma prevalence and severity suggests air pollution and climate changes could be contributing. Pollen allergy is frequently used to study the interrelationship between air pollution and rhinitis and bronchial asthma. Epidemiologic studies have demonstrated that urbanization; high levels of vehicle emissions and westernized lifestyle are correlated to an increase in the frequency of pollen-induced respiratory allergy prevalent in people who live in urban areas compared to those who live in rural areas. Meteorological factors (temperature, wind speed, humidity, etc) along with their climatological regimes (warm or cold anomalies and dry or wet periods, etc), can affect both biological and chemical components of this interaction. In addition, by inducing airway inflammation, air pollution overcomes mucosal barrier priming allergen-induced responses. In conclusion, climate change might induce negative effects on respiratory allergic diseases. In particular, the increased length and severity of pollen season, the higher occurrence of heavy precipitation events and the increasing frequency of urban air pollution episodes suggest environmental risk factors will have a stronger effect in the next decades.

Climate change and respiratory disease

The key climate change factors which could potentially respiratory disease are extreme temperature events (both heat and cold), changes in air pollution, flooding, damp housing, thunderstorms, change in allergen disposition and consequent allergies, forest fires and dust storms effects either being short-or long-term. The main areas of concern are asthma and rhino-sinusitis. COPD and respiratory tract infections but the extent to which these will be impacted will vary according to the proportion of susceptible individuals in a given population. Areas of greater poverty with limited access to medical services will suffer more as will those areas with less well developed medical services which will include migrating populations and those where population growth is greatest.

Recent findings show that experimental warming induce an advanced flowering and fruiting phenology for species that began to flower before the peak of summer heat but delayed reproduction in species that started flowering after the peak temperature in a prairie in North America. Among the latter species, authors underlined the delayed flowering of ragweed (Sherry RA, Zhou X, Gu S, Arnone JA 3rd, Schimel DS, Verburg PS, Wallace LL, Luo Y. Divergence of reproductive phenology under climate warming. Proc Natl Acad Sci U S A. 2007 Jan 2;104(1):198-202).

With warming over the longer term, changing patterns of plant habitat and species density are likely, with gradual movement northward. However, the change in land use might also play a relevant role, especially for some important allergenic species, such as graminaceae.

Since most of the data come from the analysis of distribution of airborne pollen, these findings are potentially biased by the occurrence of long and medium distance transport episode of allergenic pollen as shown in several European countries.

Pollinosis is frequently used to study the interrelationship between air pollution and respiratory allergy. Climatic factors (temperature, wind speed, humidity, thunderstorms, etc) can affect both components (biological and chemical) of this interaction. By attaching to the surface of pollen grains and of plant-derived particles of paucimicronic size, pollutants could modify not only the morphology of these antigen-carrying agents but also their allergenic potential. In addition, by inducing airway inflammation, which increases airway permeability, pollutants overcome the mucosal barrier and could be able to “prime” allergen-induced responses.

There are also observations that a thunderstorm occurring during pollen season can induce severe asthma attacks in pollinosis patients. After rupture by thunderstorm, pollen grains may release part of their cytoplasmic content, including inhalable, allergen-carrying paucimicronic particles.

An individual’s response to air pollution depends on the source and components of the pollution, as well as on climatic agents. Indeed, some air pollution-related episodes of asthma exacerbation are due to climatic factors that favor the accumulation of air pollutants at ground level and some cities are continuously affected by black smog caused by motor vehicles.


References (papers published on this topic by my group).

  1. D’Amato G.Urban air pollution and plant-derived respiratory allergy: a review. Clin Exp Allergy 2000;30:628-36.
  2. D’Amato G,.Liccardi,M.D’Amato. Environmental risk factors (outdoor air pollution and climatic changes) and increased trend of respiratory allergy.Review article. J. Invest Allergol Immunol 2000;10:123-8
  3. D’Amato G,G.Liccardi,M.Cazzola. Outdoor air pollution, climate changes and increasing trend of respiratory allergic diseases. Respiratory Medicine 2001;95:606-611.
  4. D’Amato G Airborne paucimicronic allergen-carrying particles and seasonal respiratory allergy (Editorial). Allergy 2001;56:1109-1111
  5. D’Amato G,G:Liccardi, M.Cazzola. Outdoor air pollution and respiratory allergy. In "D’Amato G,Holgate S. Eds “The impact of air pollution on respiratory health". European Respiratory Monograph 2002.
  6. D’Amato G.Editorial: Outdoor air pollution, climate and allergic respiratory diseases: evidence of a link. Clin Exp Allergy 2002;32:1391-1393.
  7. D’Amato G, G.Liccardi,M.D’Amato,M.Cazzola.Outdoor air pollution, climatic changes and allergic bronchial asthma. Eur Resp J 2002-12-26
  8. D’Amato G,G.Liccardi Pollinosis and air pollution in the Mediterranean area. Allergy Clin Immunol intern (ACI Int) 2003 ;15:73-78.
  9. D’Amato G, Liccardi G, Viegi G, Baldacci S. Thunderstorm-associated asthma in pollinosis subjects. British Medical Journal, website ( 7 January 2005
  10. D’Amato G,Liccardi G,D’Amato M,Holgate ST. Environmental risk factors and allergic bronchial asthma. Clin Exp Allergy 2005;35:1113-1124.
  11. D’Amato G., Liccardi G, Frenguelli G: Thunderstorm-associated asthma in pollinosis patients. Allergy 2007;62:11-16.
  12. D’Amato G, Cecchi L,Bonini S.,Nunes C.,Annesi-Maesano I, H.Behrendt,Liccardi G,Popov T, van Cauwenbergh. Allergenic pollen and pollen allergy in Europe. Allergy 2007;62:976-90.

Gennaro D’Amato, MD
Director, Division of Respiratory and Allergic Diseases
High Speciality A.Cardarelli Hospital, Department of Chest Diseases
Napoli, Italy

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