Climate change and the diversity of its health effects
P. Vineis (&) Imperial College London
Paolo Vineis is Chair of Environmental Epidemiology at Imperial College,
. His main interests are in the field of molecular epidemiology and gene-environment interactions. He also works on climate change with the Grantham Institute for Climate Change in London
not due to it? And what about the one in 1998? Clearly
borders are fuzzy, and causal chains intricate.
Uncertain inferences on the causal nature of events also
concern the attribution to climate change of indirect health
effects, such as infectious disease outbreaks, changes in
food quality and availability, water salinization and the
ensuing epidemic of hypertension (Xun et al. 2009). Even
wars and conflicts (like in Darfur), mass migrations and
effects on mental health have been attributed to climate
change. In a survey conducted among children aged
between 2 and 9 in Bangladesh, Durkin et al. (1993) found
post-flood changes in behaviour and bedwetting. Children
were reported to have very aggressive behaviour after
floods, with a significant increase compared to the
preflood situation. A qualitative study explored the
experiences of female adolescents during the 1998 floods in
Bangladesh, focusing on the implications of sociocultural
norms related to notions of honour, shame, purity and
pollution. A number of the girls were vulnerable to sexual
and mental harassment through exposure to unfamiliar
environment of flood shelters and relief camps. Common
mental health disorders following climate-induced
displacement include anxiety, depression, post-traumatic
stress disorder, irritability, sleeplessness and suicide.
Moreover, conflict situations that may arise among farmers
in times of climate-induced natural disasters like droughts
and floods need to be addressed.
Is all of this attributable to what we call climate change?
Where are the borders between the burden of events that
would occur anyhow, particularly in low-income countries,
even in the absence of climate change, and those
attributable to the latter? How can we identify the chain of events
that eventually explains the local outbreak? Again, fuzzy
borders have to be acknowledged. It should be noted that
the effects we have described are mainly occurring or
foreseen in low-income countries, where disentangling new
threats from the old ones is not straightforward. Also not
obvious is to disentangle the complex network of
interrelated determinants of single events, like the Farraka dam,
shrimp farming and sea level rise in the case of water
salinization in Bangladesh.
Is there a methodological specificity of the science of
climate change and health (and extensively, of Global
Health)? I do not think that such science is essentially
different from Public Healthexcept for the scaleand
the usual tools of epidemiologic methodology (emphasis
on study design, search for bias and confounding, statistical
stability of the estimates) should suffice at first glance.
However, we have learnt in the investigation of the
aetiology of chronic diseases such as cancer or cardiovascular
diseases that simple tools and traditional causal reasoning,
considering a factor at a time, can be insufficient. Though
single important determinants of healthsuch as
smokinghave been easily unveiled, the challenge posed by
diseases such as breast or colon cancer requires novel
approaches. Models of causality such as BradfordHills,
that consider single risk factors, are becoming insufficient.
One of the new approaches is called systems biology.
Though we have to be sceptical towards fashions and
unwarranted expectations, there might be some analogies
between the development of systems biology in chronic
disease epidemiology and the investigation of climate
change effects (at different levels of reality, from micro to
macro). Three characteristics of systems biology have been
suggested as central: (a) the experimental/observational
data should reflect the processes of the intact system rather
than that of an isolated component; (b) data interpretation
is often conducted using methods inspired by other natural
sciences (e.g. physics, complex mathematical modelling);
(c) an analysis of non-trivial competing explanations is
conducted, and the structure of the model should reflect the
underlying mechanisms in the biological system
(Cedersund and Roll 2009). Similar postulates may apply to the
newborn science of health effects of climate change. The
analogy I propose is a challenge for epidemiologists.
Acknowledgments This research has been made possible by a
contribution of the Grantham Institute for Climate Change.