Memorandum submitted by the London School
of Hygiene and Tropical Medicine
CLIMATE
CHANGE AND
HUMAN HEALTH
1. The potential impacts of climate change
on human health
Global climate change will probably have a wide
range of health impacts as many diseases are sensitive to climate.
The IPCC Third Assessment Report[15]
currently identifies the following main mechanisms by which climate
change will affect human health.
— Changes in distribution and seasonal
transmission of malaria and other diseases that are transmitted
by insects and ticks (eg dengue, mosquito-borne viruses, leishmaniasis).
Vector-borne diseases are one of the major contributors to the
global burden of disease (according to the WHO) and are highly
sensitive to climate conditions.
— Changes in food supply due to reduced
crop yields in vulnerable areas.
— Changes in frequency and or intensity
of weather disasters, particularly floods (coastal and riverine)
and droughts.
— Increases in food and/or water borne
diseases, particularly diarrhoeal diseases, as higher temperatures
encourage the growth of micro-organisms and more erratic rainfall
increases the frequency of contamination of surface water.
— Population displacement and economic
disruption associated with climate change and sea level rise.
— The direct effects of higher temperatures
in urban populations, causing increased cardio- respiratory mortality
in relation to heatwaves. In temperate cities, increases in heat
related deaths may be more than offset by decreases in cold-related
deaths but in tropical cities the net effect is likely to be adverse.
The IPCC concluded that the negative impacts
on health will be greater than the benefits to health of climate
change and that the worst impacts will be in developing countries.
The World Health Organisation has included climate
change as one of the six environmental risk factors in the forthcoming
Global Burden of Disease assessment. Climate change research has
focused on the physical, chemical and biological impacts, and
impacts within economic sectors such as agriculture and water
resource management. Health research has been directed towards
better understanding of direct temperature effects on health,
of the seasonality of certain infectious diseases, and of the
public health consequences of extreme weather events. Predictive
models have been developed that link climate scenarios with vector-borne
disease distributions. Policy-makers should appreciate that, while
our scientific capacity to model various health outcomes of climate
change continues to evolve, it is not possible to make precise
and localised projections for many health outcomes, especially
for those that result indirectly from a sequence of impacts.
Reduced food and water supplies. Climate
change represents an additional pressure on the world food supply
system. The current IPCC assessment is that yields of cereal grains
would increase at high and mid-latitudes, but decrease at lower
latitudes. The world's food system may be able to accommodate
such regional variations at the global level. However, at the
local level, some populations may be severely affected. The UN
Food and Agriculture Organization (FAO, 1999) estimates that 790
million people in developing countries do not have enough to eat.
Environmental factors, both natural and those that are a consequence
of human activities, can limit agricultural potential. Adaptation
should be undertaken, via development of crop breeding and management
programmes for heat and drought conditions. In the near term,
adaptation strategies will improve productivity in marginal environments.
Diarrhoea is one of the most important
causes of death and morbidity, particularly of children, in developing
countries. Recent studies have demonstrated it is highly sensitive
to relatively small increases in temperature: for example, research
in Peru[16]
showed that each 1ºC increase in daily temperature resulted
in an 8 per cent increase in paediatric admissions for diarrhoea.
This suggests that predicted temperature increases over the coming
century are likely to significantly increase the impact of diarrhoeal
disease in the poorest populations (currently estimated by the
WHO as 6.5 per cent of the total burden of disease in Africa and
over 8 per cent in the poorest countries of SE Asia). The projected
increase in precipitation variability may also increase diarrhoea
morbidity by the contamination of water supplies.
Health consequences of floods and droughts.
Any increases in climate extremes (storms, floods, cyclones, etc)
associated with climate change would cause physical damage, population
displacement, and adverse effects upon food production, freshwater
availability and quality, and upon the risks of infectious disease
epidemics, particularly in developing countries. Over recent years
a number of major climate-related disasters have occurred which
have had major adverse effects on human health—including
floods in China, Mozambique, and Bangladesh, famine in Sudan,
and Hurricane Mitch which devastated Central America. Whilst these
events cannot be confidently attributed to climate change, they
indicate how vulnerable populations are susceptible to extreme
weather. There is evidence that exposure to natural disasters
may have long term impacts on mental health in adults and children.
Malaria and other vector borne diseases.
Malaria and other vector borne diseases are likely to increase
their range in a warmer climate. This is already happening, but
the relative importance of climate change, local changes in environment
and population behaviour, and collapse of public health control
measures, is unclear in most situations[17].
Changes in rainfall distribution throughout the year and its intensity
are more important (and less predictable) for malaria transmission
than temperature increases. There is good evidence that El Niño
affects epidemic risk in certain regions[18].
The important extensions of actual malaria occurrence due to climate
change, as distinct from the potential for malaria to be transmitted,
are likely to be in those tropical countries with high altitude
areas where the population of the hills are free from malaria
but are surrounded by plains in which malaria is highly endemic.
Here, the spread of both the vector and the malaria parasites
can easily follow changes in climatic suitability. So far, extensions
laterally into higher latitudes have been more due, at any rate
in Asia, to failures of public health measures than climatic changes.
Public health measures, well applied, should be able to control
epidemics and unstable malaria at the edges of its distribution.
Climate change is unlikely to have a large effect on the severity
or transmission of malaria in those countries of tropical Africa
where there is already massive transmission and suffering from
the disease.
Arboviruses (insect-borne virus diseases)
provide a less predictable and perhaps more disturbing threat
than does malaria in relation to global climate change. Climate
change may facilitate their spread to the more temperate developing
countries and it is less predictable which will emerge as major
problems. Several arboviruses can give rise to fatal illness (for
example, yellow fever, dengue haemorrhagic fever) for which treatment
is not feasible and few have vaccines available.
3. Which populations are the most vulnerable?
There are many uncertainties in assessing the
potential health impacts as climate change scenarios are highly
uncertain at the spatial and temporal resolution most appropriate
for health impact assessment. The largest source of uncertainty
is the future world in which the climate impacts are felt—will
it be more or less equitable with better or worse health care?
Therefore, research activities have shifted towards identifying
those populations most vulnerable to the health impacts of climate
change. For example:
— Populations in currently malaria-free
areas in the East African Highlands are vulnerable to increases
in malaria associated with climate change.
— Populations in Bangladesh are vulnerable
to health impacts of flooding associated with climate change.
— Populations in central America are
vulnerable to increases in flood and landslide risk, and also
drought risk, due to any increase in rainfall variability, including
possible more frequent and intense El Niño events.
4. Clean energy and the health benefits of
mitigation policies
Actions taken to reduce greenhouse gas emissions
are very likely to benefit health. Fossil fuel combustion releases
both local hazardous air pollutants (particulates, ozone, nitrogen
oxides and sulphur dioxide) and greenhouse gases. Hence, policies
to reduce greenhouse gas emissions via a reduction in vehicle
exhausts or via an increase in the efficiency of indoor household
cookstoves (particularly in low income countries) would yield
substantial benefits to health. Controlling road traffic would
also benefit health through reductions in road traffic accidents,
a leading cause of death world-wide. The benefits to health from
mitigation are highly dependent on the technologies and sectors
that are involved. For example, a significant number of premature
deaths could be prevented via reductions in particulate emissions
in the household sector in China (ie domestic fuel use). Large
numbers of people lack access to clean energy and suffer ill health
and social disadvantage as a result. Renewable energy sources,
particularly solar and wind, could help provide this much needed
energy while minimising greenhouse gas emissions and maximising
health gain. However, rigorous health impact assessment of renewable
energy technologies should be undertaken in developing countries.
5. Adaptation measures to reduce the potential
health impacts of global climate change
Adaptation measures can be used effectively
to reduce greatly many of the potential health impacts of climate
change. The most important, cost-effective and urgently needed
measure is to rebuild public health infrastructure. Many diseases
and public health problems that may otherwise be exacerbated by
climate change could be substantially prevented with adequate
financial and human public health resources. These resources would
encompass public health training programs, research to develop
and implement more effective surveillance and emergency response
systems, and sustainable prevention and control programs. Low
income countries already have spending well below that required
to control infectious disease. According to the WHO Commission
on Macroeconomics and Health the minimum level of health expenditure
to introduce and maintain essential health interventions is US$34
per person in low income countries and US$38 per person in the
least developed countries. Poor countries currently lack the needed
financial resources to meet the most basic health needs of their
populations.
Current debate on adaptation specifically to
reduce the health impacts of climate change has focused on the
following areas:
— Improved use of climate information
to forecast and control epidemics of malaria and other infectious
diseases.
— Improved surveillance of diseases
and disease vectors in order to detect any changes in distribution,
seasonality or transmission intensity, or the emergence of new
diseases.
— Heat wave early warning systems.
Epidemic forecasts begin with a crude
prediction of epidemic risk several months in advance, derived
from the long-range weather forecast. This forecast may be made
more precise several weeks in advance using vegetation and other
patterns on satellite images, allowing preventive and early response
resources to be put in place. Research is being undertaken in
East Africa to see how far this can be made an operational tool
and there are also similar plans within India. These activities
merit support since, once set up, the ongoing costs in terms of
weather forecasting and satellite imagery are low. The key
issue is linking information to response. The poorest populations
are least able to remain in a state of perpetual readiness to
cope with epidemics. Epidemic forecasting has the potential to
really alleviate the hazards to which poorer populations are exposed.
Capacity building for developing countries.
Current efforts to support capacity building have focused on national
Climate Change Vulnerability and Adaptation Assessments.
However, health impacts have not been adequately addressed in
most assessments, if at all, and the involvement of the health
sector has been minimal. WHO is developing guidelines for developing
countries to undertake health impact assessments for climate change
that address health sector participation and capacity building.
These activities could be supported by DFID.
London School of Hygiene and Tropical Medicine
January 2002
15 Climate change 2001: Impacts, Adaptation, and
Vulnerability. Contribution of Working Group II to the Third
Assessment Report of the Intergovernmental Panel on Climate Change.
Eds McCarthy et al. CUP, New York. Back
16
Checkley et al. (2000) Lancet, 355, 442-4. Back
17
Kovats et al. (2001) Phil Trans Roy Soc B, 356:
1057-10. Back
18
Kovats (2000) WHO Bulletin, 78: 1127-1135. Back
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