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Lancet Letters
Letters to The Lancet
The current issue of the British medical journal The Lancet has this rather heated
exchange between two proponents of a link between global warming and disease--Paul
Epstein and Andy Haines--and Paul Reiter, head of the Dengue Fever branch, Division of
Vector-Borne Infectious Diseases, National Center for Infectious Diseases (CDC). Dr.
Reiter's comments are at the end.
"Global warming and vector-borne disease"
Letters to the Editor Copyright 1998 The Lancet June 6, 1998
LETTER 1:
Sir--Paul Reiter (March 14, p 839) misses the main point: it is not that vector-borne
diseases have never before occurred at high elevations during especially warm years.
Rather, it is the resurgence of highland malaria, dengue fever, and their vectors in Latin
America, central Africa, and Asia during the 1980s and 1990s, coincident with three
other changes--namely, (1) the widespread and accelerating retreat of tropical summit
glaciers, (2) the upward displacement of plants, and (3) the main underlying
measurement, the upward shift of the freezing level (0°C isotherm) in the mountains
(30°N to 30°S latitudes)--150 metres since 1970, equivalent to a 1°C warming.
Insects, in the fossil record, are excellent indicators of climate change, their distribution
shifting rapidly with warming and cooling--particularly in response to changes in nighttime and winter temperatures. These temperatures have risen twice as fast as daytime
temperatures (1·86°C per 100 years vs 0·88°C per 100 years) since 1950, which is best
explained by enhanced evaporation from warmer oceans, leading to the increased
cloudiness that blocks outgoing night-time infrared radiation.
Our understanding of Earth's climate system, and the impact of our rapidly altering of the
chemical components of the lower atmosphere, are based on an n of (one earth). Pattern
recognition, consistency of data with model projections, and internal consistency among
datasets are our primary tools for evaluating trends and risks. It is axiomatic that climate
circumscribes the range of vector-borne diseases, whereas weather affects the timing and
intensity of outbreaks. Models project that global warming will provide conditions
conducive to transmission at higher latitudes and higher elevations, and four independent
sets of physical and biological data indicate climatic warming.
The global emergence, resurgence, and redistribution of infectious disease in the latter
part of the twentieth century is--as Reiter rightly argues--multifactorial, involving landuse change, local biogeography, population migration, immunological history, control
measures, and--most fundamentally--the level of socioeconomic development. We are all
concerned about emerging infectious diseases, but many are also worried about climate
change from burning fossil fuels. The true challenge in the coming decades will be to
develop healthy economies with clean energy sources.
Paul R Epstein, Center for Health and the Global Environment, Harvard Medical School,
Boston, MA 02115, USA
1 Reiter P. Global-warming and vector-borne disease in temperate regions and at high
altitude. Lancet 1998; 351: 839-40.
2 Intergovernmental Panel on Climate Change (IPCC). In: Boughton JT, Mairo Filho LG,
Callander BA, Harris N, Kattenberg A, Maskell K, eds. Climate change '95: the science
of climate change. Contribution of working group I to the second assessment report of the
IPCC. Cambridge: Cambridge University Press, 1995: 149, 370.
3 Pauli H, Gottfried M, Grabherr G. Effects of climate change on mountain ecosystems-upward shifting of alpine plants. World Resources Rev 1996; 8: 382-90.
4 Dias HE, Graham NE. Recent changes in tropical freezing heights and the role of sea
surface temperature. Nature 1996; 383: 152-55.
5 Easterling DR, Horton B, Jones FD, et al. Maximum and minimum temperature trends
for the globe. Science 1997; 277: 363-67.
LETTER 2:
Sir--Paul Reiter1 incorrectly quotes me as making "adamant" claims that global warming
has already caused malaria, dengue, and yellow fever to invade higher latitudes in the
temperate regions and high altitudes in the tropics. Reiter's statement seems to be based
on a misquote from a Lancet news article, in which I state, "there are some early signs of
malaria and other vector-borne diseases being experienced at higher altitudes than was
previously the case". I made no comment about higher latitudes in temperate countries,
where in most cases public health infrastructure is likely to be adequate to prevent
substantial increases in incidence.
Recent reports, for example on Ethiopia and Kenya (Githeko A, personal
communication), suggest shifts in altitude in malaria consistent with increases in
temperature. Increases in temperature might be associated with increased incidence of
malaria in the Usumbara mountains of Tanzania, and increases in temperature and
rainfall have been associated with a steep rise in malaria cases in Rwanda. Changes in
climate may be due to interannual variability, climatic cycles such El Niño, local
deforestation, or global climate change; indeed all four may co-exist. Lindsay and
Martens have shown with mathematical modelling that such changes in incidence are
likely to occur with climate change, but clearly other factors may also be at work
including those outlined by Reiter. The historical data on high altitude transmission of
malaria cited by Reiter do not necessarily mean that climate change will not effect the
incidence of malaria at high altitudes.
I have argued consistently for better monitoring of the potential health impacts of climate
change to improve understanding of associations between short-term climate variablility,
longer term underlying trends in global climate, local environment change, changes in
public-health infrastructure on the one hand, and the occurrence of vector-borne diseases
and other potential impacts on health of global warming on the other.
Andy Haines, Department of Primary Care and Population Sciences, Royal Free and
University College London School of Medicine, London NW3 2PF, UK
1 Reiter P. Global-warming and vector-borne disease in temperate regions and at high
altitude. Lancet 1998; 351: 839-40.
2 McCurry J. Physicians add their warnings to Kyoto summit. Lancet 1997; 350: 1825.
3 Tulu A. Determinants of malaria transmission in the highlands of Ethiopia: the impact
of global warming on mortality and morbidity ascribed to malaria. London University,
PhD Thesis, 1996.
4 Matola YG, White GB, Magayuka SA, et al. The changed pattern of malaria endemicity
and transmission at Amani in the eastern Usambara mountains, north-east Tanzania. J
Trop Med Hyg 1987; 90: 127-34.
5 Lindsay S, Martens WJM. Malaria in the African highlands: past, present and future.
Bull World Health Organ (in press).
PAUL REITER'S REPLY
Sir--Paul Epstein is absolutely correct: I try, but am quite unable to see his point. I feel
like Alice in her conversation with the White King: "I see nobody on the road," said
Alice "I only wish I had such eyes," the King remarked in a fretful tone. "To be able to
see Nobody! And at that distance too!"
The global warming notion is far from being universally accepted. Moreover, as a
medical entomologist, I am disturbed by the tangle of syllogistic delusions in the health
aspects of the debate, and the Machiavellian way in which they are presented to the
public. For example, at his Kyoto press conference, Epstein stated: "Malaria is now
occurring in the . . . highlands of Papua New Guinea. This is exactly in the same area
where glaciers are retreating and plants are migrating up mountains". True, but even in
the 1940s scientists warned that "with the march of civilization into the highlands there
was every chance that the malaria problem could become . . . severe". They described
large populations of malaria-free so-called stone-age peoples who had been discovered in
a unique state of isolation in these highlands. To protect them, labourers entering from
the malarious lowlands were held in compulsory quarantine for weeks and given curative
malaria therapy. The eventual failure of this measure was exacerbated by anopheline
populations that increased rapidly after forest clearance and other human activities.
Malaria transmission was never attributed to climate change, by malariologists.
In the context of global climate change, Andrew Haines' arguments are equally
misleading. For example, the article he cites on malaria in Tanzania clearly states: "There
was a pronounced warming . . . at Amani during the 1960s when considerable forest
clearance occurred on the Amani hills, followed by a cooling trend as re-forestation
progressed". The statement is supported by a graph of mean annual temperature that
shows a steady decline (total 3°C) from 1970 to 1976. Clearly this was an effect of the
local environment on the local meteorology, not a global impact on the regional climate.
The principal reasons for the rise in malaria were carefully described: (1) a sizeable
influx of people from malarious lowlands, and (2) major ecological disturbance-deforestation, road construction, proliferation of dams, ditches, pools, &c--which opened
up the area to Anopheles gambiae and An funestus, the classic African malaria vectors.
Moreover, the altitude (600-1000 m) was well below the 2600 m maximum for
transmission in neighbouring Kenya, first observed in the early half of the century. Last,
Haines' mention of a mathematical model is a classic example of irrelevant proof, for it
has long been common knowledge that vectorial capacity is a function of temperature.
The model is based on this relation, so, inevitably, it indicates that incidence might
increase with warmer climate.
Like Epstein, I worry about climate change, but my concern is with the dissemination of
fallacious logic to journalists who are more likely to focus on crisis than on reason. I
stand firmly by my original message: however worthy the cause, the distortion of science
to make dramatic predictions of unlikely disasters is not in the public interest.
Paul Reiter, Dengue Branch, Division of Vector-Borne Infectious Diseases, National
Center for Infectious Diseases, Centers for Disease Control and Prevention, Dengue
Branch, San Juan, PR 00921, USA (e-mail: [email protected])
1 Carroll L. Alice's adventures in wonderland, and through the looking-glass and what
Alice found there. Oxford: Oxford University, 1983.
2 Kerr RA. Greenhouse forecasting still cloudy. Science 1997; 276: 1040-42.
3 Peters W, Christian SH, Jameson JL. Malaria in the highlands of Papua and New
Guinea. Med J Australia 1958; 2: 409-16.
4 Peters W, Christian SH. Studies on the epidemiology of malaria in New Guinea. Part
IV. Unstable highland malaria: the clinical picture. Part V. Unstable highland malaria: the
entomological picture. Trans R Soc Trop Med Hyg 1960; 54: 529-48.
5 Attenborough RD, Burkot TR, Gardner DS. Altitude and the risk of bites from
mosquitoes infected with malaria and filariasis among the Mianmin people of Papua New
Guinea. Trans R Soc Trop Med Hyg 1997; 91: 8-10.
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