Climate change futures: health, ecological and economic dimensions

Health is the final common pathway of the natural systems we are part of, and climate instability is altering thepatterns of disease and the quality of our air, food and water. The following case studies integrate the multipledimensions of diseases whose range and prevalence are affected by climate. The studies are approached from theperspective of a disease or condition (for example, malaria and asthma), a meteorological event (for example,a heat wave and flood) or from the view of natural and managed Earth systems (agriculture, forests, marineand water). The cases are organized according to background, the role of climate, health and ecological impacts,economic dimensions, scenario projections and specific recommendations to reduce vulnerabilities.Primary prevention for all the illnesses and events addressed include measures to stabilize the climate.INFECTIOUS ANDRESPIRATORY DISEASESextremes can work alone and in combination to influencethe prevalence and dynamics of a tropical vectorbornedisease, and, by extrapolation, how changesmay occur in temperate regions at the margins ofmalaria’s current distribution.THE ROLE OF CLIMATE32 | INFECTIOUS AND RESPIRATORY DISEASESCASE STUDIESMALARIAKristie L. EbiNathan ChanAvaleigh MilneUlisses E. C. ConfalonieriBACKGROUNDMalaria is the most disabling vector-borne diseaseglobally and ranks number one in terms of morbidity,mortality and lost productivity. Some 40% of theworld’s population is at risk of contracting malaria,and roughly 75% of cases occur in Africa, with theremainder occurring in Southeast Asia, the westernPacific and the Americas (Snow et al. 2005). Up to75% of cases occur in children, and over 3,000 childrendie from malaria each day (WHO 2003).Plasmodium falciparum is one of four types of malariaand is responsible for the majority of deaths. Whileadvances in antimalarial drugs and insecticides in thefirst half of the 20th century led to the optimistic viewthat malaria could be eradicated, widespread drug andpesticide resistance, and the subsequent failure of controlprograms, proved this optimistic view wrong and theworld is currently experiencing an upsurge in malaria.The three facets of this case study examine the impactsof flooding on malaria in Mozambique, the indirectimpacts of drought on malaria distribution in northeastBrazil, and the projected impacts of warming andaltered precipitation patterns affecting the potentialrange of malaria in the highlands of Zimbabwe. Thesestudies serve as examples of how warming and weatherClimate constrains the range of malaria transmission whilefloods (and sometimes droughts) provide the conditions forlarge outbreaks. Warming, within the viable range of themosquito (too much heat kills them), boosts biting andreproductive rates, prolongs breeding seasons and shortensthe maturation of microbes within mosquitoes.For malaria transmission to occur, a mosquito musttake a blood meal from someone with malaria, incubatethe parasite, then bite an uninfected person andinject the parasite. Warmer temperatures speed up thematuration of the malarial parasites inside the mosquitoes.At 20°C (68°F), for example, Plasmodium falciparummalarial protozoa take 26 days to incubate;but, at 25°C (77°F), the parasites develop in half thetime (McArthur 1972). Anopheline mosquitoes thatcan transmit malaria live only several weeks. Thuswarmer temperatures permit parasites to mature intime for the mosquito to pass it on to someone previouslyuninfected.Malaria is circulating among populations living at lowaltitudes and increasingly in highland areas in Africa.Heavy rains create mosquito breeding sites alongroadways and in receptacles (though flooding cansometimes have the opposite effect, washing mosquitoeggs away). Droughts can lead to upsurges of malariavia another mechanism: encouraging the migration ofhuman populations into (or out of) malarious areas.Climate change is compounding other changes influencingthe distribution of malaria. Population migrations, deforestation,drug and pesticide resistance also contribute andpublic health infrastructure has deteriorated in manycountries (Githeko and Ndegwa 2001; Greenwood andMutabingwa 2002). But, as climate changes, warmingand weather extremes are likely to play expanding rolesin the spread of malaria (McMichael et al. 2002).