• Mississippi •Grijalva
«•Sebou Moulouya • .Senegal Nile Volta ••Niger
• Sao Francisco
FIGURE 1-5 Relative vulnerability of coastal deltas as indicated by estimates of the population potentially displaced by current sea-level trends to 2050 (extreme >1 million; high 1 million to 50,000; medium 50,000 to 5,000). Climate change would exacerbate these impacts.
SOURCE: Figure TS.8 in IPCC (2007b).
A study in six sub-Saharan African countries showed the potential for HIV/ AIDS to amplify the effects of drought on childhood malnutrition, particularly in periurban and urban populations where HIV prevalence was high (Mason et al., 2005). Malnutrition associated with drought increases susceptibility to diseases such as measles, particularly in countries such as Somalia where immunization rates are low (Shepherd-Johnson, 2006).
Drought has variable effects on the incidence and distribution of vector-borne diseases such that, for example, reductions in mosquito activity during droughts may be followed by increases in disease transmission once the drought ends because of the increased number of susceptible hosts (Woodruff et al., 2002). In other cases, stagnation of water in residual pools may cause short-term increases in the transmission of malaria. Long-term drought may result in the contraction of areas suitable for malaria transmission.
Assessment of the likely effect of climate change on malnutrition is complex because the impacts on food production and consumption depend on a range of factors, including agricultural practices, the potential role of carbon dioxide fertilization in improving some crop yields (the effect of increasing concentrations of carbon dioxide in improving the yields of some crops may be reduced when crops are stressed as a result of high temperatures or changes in precipitation), patterns of land ownership, and the ability of disadvantaged populations to purchase food. Concern has also been expressed about the potential competition for land between biofuels and agricultural production for food, although this is not an inevitable consequence and will depend on the policy choices that are made (Haines et al., 2007). Vulnerability to increased malnutrition as a result of climate change is likely to be greatest in regions currently most vulnerable to food insecurity, particularly sub-Saharan Africa (FAO, 2005).
Both fatalities and direct economic losses of national per capita income from natural disasters are higher by orders of magnitude in low- and middle-income countries compared to high-income countries (Linnerooth-Bayer et al., 2005). For example, a study of the impact of Hurricane Mitch on the livelihood of rural poor in Honduras showed that one of every two households surveyed incurred medical, housing, or other costs due to the hurricane. Relief amounted to less than one-tenth of the losses incurred by households (Morris et al., 2002). Such economic losses accentuate poverty and contribute substantially to the adverse effects of climate-related disasters on public health. For example, an estimate of mortality due to floods in Mozambique in 2000 suggested that the increase in infant mortality associated with around a 14 percent drop in gross domestic product in the flooded provinces made a substantial contribution to the overall deaths due to flooding (Cairncross and Alvarinho, 2006).
70 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS
Is There Evidence That Climate Change Has Begun to Affect Human Health?
There is good evidence that climate change has caused an earlier onset of the spring pollen season in the Northern Hemisphere, with resulting changes in the seasonality of allergic rhinitis (Emberlin et al., 2002). The summer of 2003 was probably the hottest in Europe since 1500, and climate change is thought to have at least doubled the risk of a heat wave such as that experienced in 2003 (Stott et al., 2004).
However, in the case of infectious diseases there is still considerable controversy about the degree to which climate change has been responsible for changes in the incidence and distribution of disease. This is due to the potential contribution of other factors, such as changing land use patterns, human behavior, and methodological issues, including the use and analysis of appropriate climate data. Northern shifts in tick distribution have been observed in Sweden (Lindgren et al., 2000), and the incidence of tick-borne encephalitis (TBE) in Sweden has increased considerably since the mid-1980s. A study of cases of TBE in Stockholm County between 1960 and 1998 showed that increases in disease incidence were significantly related to a combination of two consecutive mild winters, as well as temperatures favoring spring development and extended autumn activity in the prior year, and temperatures allowing activity early in the incidence year (Lindgren and Gustafson, 2001). This suggests that milder winters and the early arrival of spring may have contributed to the increased incidence of TBE, but other factors may be implicated, such as changes in land use and land cover leading to increases in the wildlife hosts of ticks, together with the presence of more people in endemic locations (Randolph, 2001).
There has been considerable interest in the possible role of climate change as a factor in the increases in malaria incidence in the East African highlands over recent decades. Using an analysis of data for four sites, Hay and colleagues (2002) asserted that there were no significant trends in climate variables and therefore concluded that climate change had played no role in malaria resurgence in the region. However, the use of low-resolution data to investigate the relationship was criticized, and it was suggested that the apparent lack of an association could not be interpreted as convincing evidence that climate change had not played a role (Patz, 2002). Subsequently, an updated time series (Pascual et al., 2006) using an additional 5 years of data demonstrated that, using both nonparametric and parametric statistical analyses, there was evidence of significant warming trends of around 0.5°C at all sites. It was suggested that the "observed temperature changes would be significantly amplified by the mosquito population dynamics with a difference in the biological response at least 1 order of magnitude larger than that in the environmental variable" (Pascual et al., 2006).
Other authors have shown that climatic factors play a role in malaria epidemics in the East African highlands. The study of climate variability, seasonality, and
the number of monthly malaria outpatients over 10- to 15-year periods in seven highland sites in East Africa showed substantial spatial variation in the sensitivity of malaria outpatient numbers to climate variability, with between 12 and 63 percent of variance attributed to climate variability (Zhou et al., 2004). The study of malaria epidemic risk in Ethiopia showed that epidemics were significantly more often preceded by a month of abnormally high minimum temperature during the previous 3 months than would be expected by chance (Abeku et al., 2003).
The recent United Nations Development Programme (UNDP) Human Development Report (UNDP, 2007) has documented the growing burden of climate disasters, which is greater than can be explained by population growth alone. Weather-related insurance losses are increasing faster than the population, inflation, and coverage, but the greatest impacts are in developing countries where the majority lack insurance. Between 2000 and 2004, more than 250 million people per year were affected by hydrometeorological disaster (with increases in floods, droughts, lightning strikes, and the intensity of tropical cyclones), compared to less than 50 million per year between 1975 and 1979. A recent report has documented the contribution of increased sea surface temperature to increased Atlantic hurricane activity in recent years (Saunders and Lea, 2008).
Estimating the Impact of Climate Change on Infectious Diseases
A growing number of studies that have modeled projected impacts of climate change on health have been reviewed by the IPCC (IPCC, 2007b). A study of the potential effect of climate change on malaria transmission in Africa that assessed the impacts of 3 climate scenarios suggests a modest (5 to 7 percent) increase in the population at risk, largely due to expansion into higher altitudes. It also suggested a prolongation of the transmission season in some areas, leading to a 16 to 28 percent increase in the total number of person-months exposure (Tanser et al., 2003). This analysis, although based on a very large database of historical malaria surveillance data, has been criticized for oversimplifying the situation (1) by underestimating the variability in response of local vector species to climatic change and (2) because extension of the transmission season does not necessarily translate into a proportional increase in mortality or clinical disease (Reiter et al., 2004). Inevitably, however, all models involve some simplification of assumptions, and for example, few studies take adaptive capacity into account.
Exercises to estimate the global burden of disease due to climate change have been undertaken under the auspices of the World Health Organization (WHO). Epidemiological models were used to estimate the impact of climate change on a number of health outcomes (malaria, diarrheal disease, malnutrition, flood deaths, and direct effects from the heat and cold). The analysis suggests that although there are likely to be some benefits, particularly lower cold-related mortality in temperate zones, these benefits will be greatly exceeded by negative impacts on health, particularly in terms of infectious diseases and malnutrition in low-income
countries. The methodological approach has been outlined elsewhere (McMichael et al., 2004), and on aggregate, the estimates suggest that compared to baseline, climate change had caused around 150,000 deaths annually by 2000, an equivalent to 0.3 percent of global deaths per year or 0.4 percent of global disability-adjusted life-years (DALYs) lost annually. The estimate may well be conservative because the baseline used was the average climate for 1960-1991 when climate change was probably already under way and the range of health outcomes was limited. Although increasing wealth and some level of adaptation could blunt the adverse effects, it is likely that the disease burden as a result of climate change will increase substantially over time and will be particularly concentrated in the poorer populations. Nevertheless, populations in all regions of the world are likely to experience some adverse effects, particularly if temperature increases exceed 2°C, at which temperature the probability of major adverse events—such as melting of ice caps and disruption of ecosystems—appears to be unaccept-ably high, as judged for example by policy makers of the European Union (EU) who have undertaken to pursue negotiations with the aim of keeping temperature increases below that level (European Commission, 2007).
Adaptation to climate change may take a number of forms; physiological and behavioral adaptation may take place without policy changes, but properly designed adaptation strategies can result in near-term benefits to public health, as well as improving the resilience of populations to future climate change. Policies to improve access to clean water and sanitation, promote hygiene behaviors, promote uptake of immunization, and strengthen health systems are needed in any event in order to improve the chances of attaining the UN Millennium Development Goals (Haines and Cassels, 2004). Increased use of insecticide-impregnated nets and appropriate antimalarial drug combinations that take into account prevailing patterns of drug resistance, as well as effective vector control strategies such as indoor residual spraying, can all help to reduce the burden of malaria.
The threat of climate change has resulted in increased interest in climate-based early warning health systems for heat waves and climate-sensitive diseases. Early warning systems must be integrated into local health systems if they are to have an impact. One example is the highland malaria project (HIMAL), which aims to create and test functional systems for malaria early warning and early detection including district-level surveillance and predictive modeling (Abeku et al., 2004). Most routine disease surveillance systems lack the ability to provide accurate and timely indications of increases in the number of cases of malaria. There is a need to improve the routine collection of data on parasitologically confirmed cases of malaria because febrile illnesses other than malaria have to be considered as possible causes of outbreaks (Cox et al., 2007). Seasonal forecasts can also be used to increase preparedness for climate variability and extreme
events associated with phenomena such as El Niño; these approaches were used to warn specific governments when a strong El Niño was developing in 19971998 (Hamnett, 1998).
Meeting the Energy Needs of the Poor While Reducing Greenhouse Gas Emissions
Meeting the energy needs of the poor will also help to reduce vulnerability to climate change. Currently there are around 1.6 billion people without electricity (Modi et al., 2006), and 2.4 billion use solid fuels (wood, dung, coal) in their households. Meeting the essential energy needs of the poor will take around 1 percent of current world energy use and in addition reduce exposure to high levels of indoor air pollution (with an attributable annual mortality of about 1.6 million) (WHO, 2002). Concerted action is needed to improve access to more efficient cook stoves and to assist poor populations to move to cleaner fuels, such as kerosene, liquefied petroleum gas, or biogas. Electrification, using renewable energy where possible, can improve adaptation by supplying electricity to maintain the cold chain for vaccines, to provide a reliable power source for health facilities, and to make possible the use of information and communication technologies. The need for policies that prevent dangerous anthropogenic interference with the climate while addressing the energy needs of disadvantaged people is an essential challenge for the current era (Haines et al., 2007).
Although most renewable energy technologies can provide near-term benefits for health, for example by reducing exposure to air pollution, as well as mitigating greenhouse gas emissions, it is important that health impact assessments are undertaken. For example, a range of public health problems related to dams (which can be used to generate hydroelectricity and to promote adaptation to climate change through improved irrigation) have been documented, including increases in the prevalence of schistosomiasis, the introduction of Rift Valley fever, and increases in the burden of malaria. A recent systematic review concluded that although it was not possible to quantify the attributable fraction of the malaria burden due to dam building and irrigation, future water resource development projects should include in-depth assessment of potential effects (Keiser et al., 2005).
Climate change is likely to have far-reaching implications for human health and development. The Stern Review (Stern, 2006) has extensively reviewed the economic rationale for mitigation and adaptation polices, and also suggested that there is a strong economic case for action in the near term because the effects of climate change could result in losing around 5 percent of the gross world prod-
74 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS
uct (GWP) by the middle of the twenty-first century, perhaps even reaching 20 percent or more if the full range of effects is considered.
Infectious diseases are one of a number of categories of health outcomes that are likely to be affected adversely by climate change. Public health policies should take into account the need to adapt to a changing climate, as well as the potential for near-term benefits to health from a range of policies to mitigate climate change. Research funders should increase resources available to improve our understanding of the linkages between climate change, other environmental changes, and human health.
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