Abstract Climate change&apos;s burden of disease seems orders of magnitude too low to justify claims that it is this century&apos;s greatest threat to health. However, such claims can be more easily understood by considering how climate change acts as a risk multiplier, compounding pre-existing socially and politically-mediated drivers of adverse health consequences including conflict

Colin D Butler

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Climate change and global health: a new conceptual
framework - Mini Review
Colin D. Butler
Abstract
Climate change’s burden of disease seems orders of magnitude too low to justify claims that it is
this century’s greatest threat to health. However, such claims can be more easily understood by
considering how climate change acts as a risk multiplier, compounding pre-existing socially and
politically-mediated drivers of adverse health consequences including conflict.
Is Climate Change the Biggest Global Health
Threat of Our Time?
A widely cited paper characterized climate change as this
century’s greatest threat to health [1]. However, the 29
authors of this paper, the longest ever published in The
Lancet, are vague concerning their reasons for this strong
claim. About a decade ago, the World Health Organiza-
tion undertook a comprehensive study of the burden of
disease of climate change, concluding that in 2000 it was
about 160 000 deaths per annum, with 5.5 million lost
disability-adjusted life years (DALYs). These were mainly
due to climate change related undernutrition, with minor
contributions from infectious diseases (especially malaria
and diarrhoea), heatwaves and floods [2,3]. Such numbers,
even if accurate, were insignificant as a proportion of
the global burden of disease in 2000, which was almost
1.5 billion DALYs [4]. They would have to rise by orders
of magnitude to justify the claim as the greatest threat to
health we face. Nor do the health chapters in the Inter-
governmental Panel on Climate Change (IPCC) reports
[5] hint that this dire prediction might be valid.
Primary, Secondary and Tertiary Health
Effects – an Emerging Classification
However, such claims may not only be justifiable but also
more easily understood if the commonly used bi-modal
categorization of the health effects of climate change is
widened to include a separate category that explicitly
recognizes the interaction between the environmental
effects of climate change and the social and political
‘milieu’ in which they operate. A recent edited book,
assembling a group of 56 authors from 19 countries,
sympathetic to this broad conceptual framework attempts
to consolidate this causal classification [6]. This third class
concerns future adverse health effects arising from harm
to the economic and social determinants of health
occurring as a consequence of future climate change.
Discussion of these ‘eco-social’ effects is still limited in
the health literature, particularly in comparison to their
potential scale.
In the past, relevant literature (including a previous
edited book on climate change and health) have focused
mostly on pathways described as ‘direct’ (such as from
heatwaves or injury due to a flood or storm) and ‘indirect’
[7]. The latter generally are dominated by changes in
infectious diseases, but other less direct, climate change
related mechanisms are known to impact health, such as
via altered timing and concentrations of allergens or
hypertension from increasingly saline ground water in
coastal Bangladesh exacerbated by sea level rise [8].
If considered at all, the politically-mediated, systemic
effects are also usually also considered ‘indirect’, but
mostly as a footnote. Recognizing this conceptual gap, and
at the same time wanting to promote recognition of the
potential severity of the health consequences of climate
change, Butler et al. [9] proposed a four-way classification
of effects, which they called ‘direct’, ‘mediated’, ‘modu-
lated’ and ‘systems failure’. Later, this was simplified by
merging the final two forms into a group was then called
‘tertiary’ [10]. This revision also changed the names of
‘direct’ and ‘mediated’ to ‘primary’ and ‘secondary’.
‘Primary’ effects operate most directly on humans, such
as through acute or prolonged heat stress, especially a
problem for vulnerable people on hot nights, or emer-
gency personnel engaged in strenuous exercise. Second-
ary effects include changes to the distribution of vectors
that spread malaria and other vector-borne diseases.
Butler and his three co-authors held that the third
category – whatever its name – warranted separate dis-
cussion for several reasons. All three categories arise
from the interaction of anthropogenic climate change
and ‘eco-social’ causes. However, causation becomes
increasingly ‘indirect’, with each successive category. For
example, there is less debate that a heatwave harms
health, even though its health burden is mediated by non-
climatic factors such as housing, air conditioning and the
effectiveness of emergency services. Climate change
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CAB Reviews 2014 9, No. 027
aggravated malaria [11], here grouped in the ‘secondary’
category, also arises through the interaction of climatic
change, ecological factors (e.g. the distribution of vectors)
and social and economic determinants.
The association of malaria (and other infectious dis-
eases) with climate change has, in fact, been intensely
contested [12]. But the third, tertiary, classification is
distinguished by the greatest causal complexity and
indirectness. Tertiary health consequences are modified
by numerous cultural, political, economic, social and other
effects such as poverty, inequality, population growth,
resource scarcity and governance. But this complexity
should not be used to argue there is no climatic compo-
nent, which will be become increasingly obvious (and
accepted) with time. Butler et al. [9] also argued that the
likely health impact of such effects, perhaps by as soon as
2050, could be orders of magnitude greater than from
heatwaves, allergens or vector-borne diseases (even if
combined). This scale difference constituted an additional
justification for a separate category.
Late last century it was briefly fashionable to argue that
humanity had finally solved its ancient problem of scarcity.
This fantasy is slowly being replaced by a re-awakening
that immense problems persist, and that the declining
availability of essential resources, including because of
climate change, will worsen hunger and increased under-
nutrition in many populations [13]. However, it is still
underrecognized that these consequences will have their
own ramifications, generating cascading effects likely to
include decreased health system capacity, reduced funding
to improve other health determinants, and increased
migration and conflict.
Discussion of the tertiary effects is unsettling territory
for many within medicine and even some within public
health, as some regard the causal pathways involved as
too ‘upstream’ [14] or ‘political’ [15,16]. Partly as a result,
these pathways have received grossly insufficient attention
within the health literature, though there is growing
concern about the consequences for society in some
other disciplines (notably ecology) and within society
more broadly [17].
This is not to say that tertiary effects (however classi-
fied) have been entirely ignored. The earliest editorial on
climate change and health in The Lancet (and perhaps in
the entire health literature) mentioned the possibility of
conflict [18]. However, there has been little consolidation
of this thinking, including in the most recent IPCC chapter
(to which the author contributed) [5].
There are several exceptions not mentioned above.
McMichael et al. [2] noted that “the conflicts and the
migrant and refugee flows likely to result from these
wider-ranging effects would, typically, increase infectious
diseases, malnutrition, mental health problems, and injury
and violent death. They commented that ‘future assess-
ments of the health effects of climate change should
attempt order-of-magnitude estimates of these more
diffuse risks to health.’ Myers and Patz [19] wrote ‘It may
be that scarcity of food and water combined with greater
vulnerability to natural disasters and forced migration
will lead to much higher morbidity and mortality than
increased exposure to infectious disease.’ A recent
magazine article by one of these authors is even closer to
the arguments presented here: ‘we believe that there is
another threat, one that is orders of magnitude more
potent than those which have been emphasized to date.
Here we argue that it is the indirect impacts of climate
change – large-scale alterations to Earth’s natural sys-
tems – that pose the greatest risk to human health’. This
essay also notes the reticence of the IPCC health chapter
to engage with these issues [20].
Conclusion: From Adaption Towards a Solution
For at least a generation the dominant revealed (as
opposed to stated) global policy has been one of
attempted ‘adaptation’ to climate change, but it can be
argued that too often this has been at the expense of
mitigation. In public health terms, a focus on adaptation at
the cost of prevention is policy failure, especially where
viable preventive policies exist, as has long-been argued to
be the case for climate change (e.g. by accelerating the
roll-out of clean energy). Instead, as many have observed,
what is lacking to advance solutions for climate change is
sufficient political will [17].
To change this, a deeper understanding (and indeed a
degree of anxiety), especially among the educated masses
in rich countries, and elites everywhere is required.
Determination to act is finally emerging, for example as
shown by leaders such as UN Secretary General Ban Ki
Moon, Pope Francis, US Secretary of State John Kerry and
former UN Commissioner for Human Rights, Mary
Robinson. All have become leading, even outspoken,
advocates for policies to address climate change. They
may not be aware of the conceptualization of climate
change and health described in this paper, but they are
certainly motivated by concern over the tertiary effects.
Many developing countries, such as parts of Africa and
South Asia, appear especially vulnerable to the threat
multiplying spectre of climate change, as they are also
infected by persistent underdevelopment, conflict, pov-
erty, high population growth and other traps that afflict
the ‘bottom billion’ [21]. Many other regions, including
Syria and Yemen are also vulnerable to the risk-multi-
plying leaven of climate change in the near future (perhaps
to 2050). But as and if the juggernaut of climate change
becomes unstoppable its myriad harmful effects such as
sea level rise, intensification of extreme weather events,
ocean acidification, rising food prices and crop failure)
place even parts of civilization appear that are currently
privileged at risk [22].
Such a world of intensified haves and have-nots will
inspire growing radicalism and desperation among the
excluded, leading to both violence [23] and increasingly
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2 CAB Reviews
barbaric ‘fend’ strategies to try to deter aspiring immi-
grants [24]. Long before civilization collapses, quality of
life within the shrinking fortresses of remaining order will
plummet; unless something is done.
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Colin D. Butler 3
About the author
Colin D. Butler is a Professor of Public Health at the University of Canberra, Australia. In 2009,
the French Environmental Health Association named him as one of ‘100 doctors for the Planet’
in the countdown to the Copenhagen Climate Summit. He is the sole editor of Climate Change
and Global Health. Currently, he is a member in the Faculty of Health, University of Canberra,
ACT 2601, Australia.
doi: 10.1079/PAVSNNR20149027
The electronic version of this article is the definitive one. It is located here: http://www.cabi.org/cabreviews
g CAB International 2014 (Online ISSN 1749-8848)
Author Queries:
AQ1: Please provide page numbers in reference [5].
AQ2: Please provide year of publication, volume and page numbers in reference [16].
AQ3: Please provide email ID of Colin D. Butler for ‘About the Author’.
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Climate change and global health: a new conceptual framework

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