Climate change and health: implications for research, monitoring, and policy

Introduction

The potential effects of climate change on human health are summarised in the previous article.1 These are wide ranging and pose considerable challenges to both researchers and policy makers.2 The complexity of these environmental processes and their impact on health necessitates a multidisciplinary approach.

In environmental health there is a close relation between epidemiological research and those monitoring activities which seek evidence of changes in the environmental or health status of populations. A distinction is usually made between monitoring and surveillance, the latter being the continuing standardised recording of the occurrence of disease. In the context of climate change and health, however, both monitoring and surveillance are needed to (a) identify important changes in disease incidence, health risk indicators, or health status; (b) determine whether these changes are likely to be the result of local, regional, or global environmental changes; (c) to help develop countermeasures and assess their effectiveness; and (d) to develop hypotheses about the potential health effects of climate change. Monitoring should also help in the detection of unexpected events.3

The research challenge

Since there is uncertainty about the profile and rate of future climate change it is necessary to estimate effects on health in relation to specified probable climate scenarios. This process differs in several important ways from the more familiar empirical procedure of quantitative risk assessment.4 The latter is usually conducted in relation to some existing index of environmental exposure for which there is prior empirical evidence of direct (usually toxicological) health risks across an exposure range which includes the index exposure.

The three main approaches to health risk assessment based on scenarios are extrapolation based on specific (historical) analogue situations for some aspects of climate change; formal integrated mathematical modelling; and generalised assessments drawing on expert judgment of the range of health consequences (physical, microbiological, and psychological) of diffuse and complex demographic, social, and economic disruption.

Modelling skin cancer rates

A recent illustration of integrated mathematical modelling comes from a related topic—stratospheric ozone depletion, increased ultraviolet irradiation, and the impact on the incidence of skin cancer in fair skinned populations.12 The study modelled the excess rate of skin cancer in Europe and the United States during the coming century in response to three contrasting ozone depletion scenarios: (a) a “business as usual” scenario of gaseous emissions destroying ozone; (b) one incorporating the emission restrictions required by the protocol drawn up the Montreal meeting on substances that deplete the ozone layer in 1987; and (c) a scenario taking account of the Montreal protocol as amended in Copenhagen in 1992.

The study used an integrated model that combined metamodels of the components of the chain linking source and risk—that is, emissions, ozone depletion, changes in ultraviolet irradiance, and dose-effect (ultraviolet-cancer) models. The uncertainties in each component were included in the model. A multiple run Monte Carlo technique was used to allow for variable combinations of these uncertainties and estimated future trajectories of skin cancer incidence rates were produced. The central estimate for the third scenario was that the skin cancer incidence would peak at an increment of approximately 10% around the middle of next century. For the other two scenarios, the cancer increments were orders of magnitude larger.

An El Niño event causes temperature anomalies in the troposphere. In this false-colour satellite image of the 1983 event, red areas correspond to regions with temperature higher than the long term average; blue areas indicate regions where temperatures are lower than the long term average

NASA GSFC/SCIENCE PHOTO LIBRARY

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Dealing with uncertainty

As with all forecasting, assessing the impacts of global climate change entails unavoidable uncertainties.4 17 These uncertainties arise from the intrinsic unknown element in future trends in human industrial, demographic, and trading behaviour; from the nature of the non-linear and interactive relations within the various complex natural systems; and from the variable (and population specific) sensitivity of the health outcome to the change in climate and environment. Uncertainty also arises from the stochastic nature of the biophysical systems being modelled.

Differences in vulnerability between populations are another source of variability.18 These occur because of the heterogeneity and changeability of human culture, social relations, and behaviour. As Balbus and Patz state: “While a given disease system may be particularly sensitive to the effects of climate change based on biological or physiological characteristics, the ultimate vulnerability of a given population to that disease may be considerably lessened by adaptive responses.”19 Some populations and geographical regions will be particularly vulnerable. For example, populations whose food supplies are insecure are vulnerable to downturns in agricultural productivity caused by climatic factors, and people living on the edge of regions where infectious diseases borne by vector organisms are endemic are most likely to experience the early extensions in range of these diseases.

Another dimension of complexity in the assessment task results from the interplay of several environmental stresses that are coexistent. Interaction between local environmental degradation and changes on a larger scale—climate change, population growth, and loss of biodiversity—may significantly influence the effects on health. For example, local deforestation caused by increased population pressure may directly change the distribution of vector borne diseases while also causing a local increase in temperature (in addition to its contribution to a global temperature increase by depleting one of the biosphere's great carbon dioxide “sinks”).20

Major research needs

Important research needs include the following2:

• Improvements in mathematical models for predicting the impact of climate change on health, including higher resolution to enable local and regional impact assessments to be made;

• Further studies to (a) distinguish more clearly between the effects on health of climate and of air pollution; (b) determine the extent to which, in different regions, a reduction in mortality related to cold might offset the impact of more frequent heatwaves; and (c) assess the longer term health effects, if any, on populations living in locations with different climates;

• Analysis of infectious disease epidemics associated with recent regional changes in climate, using these as analogues of future climate change. For example, asystematic examination of vector borne outbreaks in regions affected by climatic events related to the El Niño southern oscillation would improve our understanding of the relations between climate and health;

• For vector borne diseases, there is a need for basic laboratory and field investigations of arthropod vector ecology and pathogen infectivity at raised temperatures and varying humidity and ecological studies on the climate sensitivity of diseases in locations at the margins of endemic areas;

• Assessment of how changes in food production—as a result of climate and weather changes, increased ultraviolet irradiation, sea level rise, changes in pest ecology, and socioeconomic shifts in land use practices—could affect human health and nutrition;

• Study of the association of extreme climatic events with global warming and the occurrence of disasters affecting large human populations;

• Modelling studies of the potential public health implications of forced migration from climatically vulnerable regions;

• Ecological studies of the range of possible public health impacts of reductions in biodiversity related to the climate;

• Assessment of the potential health impacts of strategies to mitigate greenhouse gas emissions (for example, the health risks of biomass fuels).

Monitoring for changes in health related indices

Policy implications

The implications of climate change for public policy are wide ranging. Policies to reduce changes are shown in the box. Mitigation options aim to reduce greenhouse gas emissions or to increase carbon dioxide sinks—for example, by promoting reforestation. Some options directly affect health, such as the promotion of bicycling, which would increase fitness and lower cardiovascular risk while helping to reduce carbon dioxide emissions.29 Renewable energy sources should be assessed for their impact on health since some may have adverse consequences. Hydroelectric dams for example may cause population displacement and social disintegration.30

Population growth is an important driving force of climate change. It is estimated that half of the increase in carbon dioxide emission between 1992 and 2022 will be a result of population growth.32 Although most will occur in developing countries, any growth in developed countries is an important contributor because of the much higher per capita consumption of fossil fuels. Currently only around 1% of international donor aid is spent on family planning, whereas just 2-3% would give worldwide access to contraception.33 Policies such as these, which meet short term local needs as well as long term environmental goals, should be priorities for implementation.

Tension between the priorities of conventional economics and environmental protection has led to the development of “environmental economics.” 34 This attempts to assign a market value to the otherwise uncounted costs of the adverse impact of environmental degradation. “Ecological economics” seeks to incorporate the concept of sustainability and thus to avoid compromising the health and survival of future generations.35 There is clearly a need for greater public and professional debate about the long term consequences of climate change and the balance between the immediate economic impact of mitigation strategies and their potential to reduce the impact on health and wellbeing in the future.

Agenda 21, the principal outcome of the 1992 UN Conference on Environment and Development held in Rio de Janeiro, indicates that many countries support an integrated approach to reducing poverty and environmental degradation. Richer countries agreed—at least in principle—to increase funding to promote “sustainable development” and to transfer information and energy efficient technology and improve education and training.36

The WHO is now seeking to persuade governments that public health considerations are a key criterion in sustainable development.37 There has already been international cooperation in phasing out compounds that cause stratospheric ozone depletion in the form of the updated Montreal protocol of 1987; this is an example of the use of a precautionary approach which yielded international action despite scientific uncertainty.38 However, in the case of climate change action has not yet matched the rhetoric. The UN Framework Convention on Climate Change urges developed countries to take the lead in combatting climate change but it will be late 1997 before concrete action on greenhouse gas emissions will be agreed for the period beyond 2000, and most nations are unlikely to reach the initial target of reducing their emissions to 1990 levels by 2000.39 The recently elected British government has announced its intention to reduce the nation's carbon dioxide emissions in 2010 to a level 20% lower than that in 1990 but clear policies need to be developed and implemented to ensure that substantial and timely reductions occur.

Meanwhile, steps could be taken to improve population adaptation to climate change—but not as alternatives to mitigation. Some, such as eliminating the breeding sites of vector organisms and improving vaccination coverage, are within the capacity of health professionals. Others, such as changes in building design to reduce heat load and improvements in flood protection mechanisms, require policy changes in other sectors.

Finally, global environmental hazards to health should feature in medical school curricula since much of the anticipated impact on health would occur within the coming decades.40 Meanwhile, in the spirit of primary prevention, health professionals should advocate to policy makers early application of strategies to minimise climate change in order to limit the anticipated impact on health. That impact, mediated through disruption to life supporting biophysical systems, has unprecedented importance for the sustainability of human health.