Climate change as a health threat: reflections on two papers in the Lancet

This is a slightly modified and longer version of an essay I wrote for Croakey, called "Climate change a great threat to health, but not as generally conceived". In the months leading to the 2009 Copenhagen climate change conference the Lancet published an unusually long (41 page) article called “Managing the health effects of climate change”. The text postulated that “climate change is potentially the biggest global health threat in the 21st century” but the executive summary was subheaded: “Climate change is the biggest global health threat of the 21st century”. 

Later this month, in the lead up to the Paris climate change summit, the Lancet is to again publish a major report on climate change and health. I had no role in either commission, though in 20014 my edited book on the subject came out. (It is to be reprinted with a new chapter in a softcover version by mud-2016.)

From 2008 until late in 2009 I was part of a WHO-led team which was trying to update the earlier study on the burden of disease (BOD) of climate change. We eventually abandoned the project. There were several reasons for this which could become another essay – but thinking about this led me to develop a figure which those with access can view here. This link is to a poster I presented at an environmental health conference in 2013, and which was also included in chapter 26 of my edited book – it attempts to convey the future burden of disease of climate change, in about 2050.

The earlier study concluded that climate change could be attributed as causing about 5.5 million lost disability-adjusted life years (DALYs). This was mainly due to climate change-related undernutrition, with minor contributions from infectious diseases and perhaps disasters. That may sound a lot, but –even if the methodology is accepted as valid - it was less than 0.4% of the global BOD in 2000. In contrast, HIV/AIDS, the leading cause of lost DALYs in the “baseline” scenario for 2030, in an updated BOD study, contributes about 12% of the total – or a proportion about 30 times as much as that of climate change did in 2000. But climate change is a risk factor, not a disease, so it is likely to cause an increased BOD for several health conditions – such as heat stroke, malaria, undernutrition, suicide and violence. However, each of those conditions has multiple causes; weighing the fraction that climate change is responsible for is bound to be disputed. Tobacco smoke, closely followed by childhood underweight, was found to be the leading risk factors in an updated BOD study published in 2013, each causing about 8% of the total burden, or about 20 times as much (as a fraction) as that of climate change in 2000.

The claim that climate change will emerge as the greatest threat to global health this century calls for strong evidence, if it is to be taken seriously. But few health workers appear to do so; if they did, then shouldn’t health workers be arguing that resources should be diverted from hospitals, medicines and primary care in order to do so? Shouldn’t climate change and health be central to every medical school curriculum? But such appeals are far from mainstream. 

Outside health, even fewer experts are concerned, including among the agricultural and political science communities. Of course, some health workers do take this warning seriously. Here I suggest several explanations.

The first may lie with the Lancet paper itself. It is vague, repetitive, and in part overstated. At one point it comments “a 13-m rise [in sea level] would cause the flooding and permanent abandonment of almost all low-lying coastal and river urban areas. Currently, a third of the world’s population lives within 60 miles of a shoreline and 13 of the world’s 20 largest cities are located on a coast. More than a billion people could be displaced in environmental mass migration.” That sounds plausible, except that neither the IPCC nor any other authority suggests any such extent of sea level rise is likely this century. Few if any peer reviewed articles suggest more than 2 metres of sea level rise this century is plausible. While there may be reasons that even 2 m is conservative, 13 m is surely exaggerated – not that the Lancet paper suggests this is likely by 2100. In fact no date is suggested at all. A perception of exaggeration may reduce the impact of this paper, contrary to the authors’ intention.

The Lancet paper identifies six main health effects from climate change: (1) changing patterns of disease and morbidity, (2) food, (3) water and sanitation, (4) shelter and human settlements, (5) extreme events, and (6) population and migration. However, no attempt is made to rigorously quantify the health effects for any of these. I can understand why, but this risks creating a perception of “hand waving”.

Another reason for the comparative lack of impact of this paper is that although its authors are consciously inter-disciplinary, the consensus in many other disciplines is far more conservative. This is exemplified by the issue of conflict. The possibility that climate change may contribute to violent climate was first raised in the health literature in 1989 (in a Lancet editorial), but has rarely surfaced since. A recent paper, by 26authors confirms the resistance of political scientists to this idea, although, outside this discipline, the idea is gaining more currency. The 2009 Lancet paper also reviews the literature at that time concerning food security and climate change. While not quantifying the risk, the message is consistently more downbeat than that of the IPCC reports, though the 2013 IPCC food chapter is less optimistic than its predecessors. If disciplinary specialists do not share the anxiety of the Lancet authors then why should generalists?

There is another reason that neither health workers nor the wider community takes the Lancet paper’s claim seriously: general incredulity. Conceding that our species is capable of critically undermining the environmental and social determinants that make civilisation possible appears to stretch our collective cognitive capacity. While many scientists (such as Will Steffen in this excellent recent lecture on the uncharted waters the Earth system is now in) and an increasing number of lay and business people (including Elon Musk) do understand this – and are rightly apprehensive, about “business as usual” the understanding that most of the world’s population has of climate science seems not much better than of evolution a century ago, or heliocentricity several hundred years before that. Adding to this difficulty, of course, are powerful vested interests that deliberately confuse and cloud public understanding and, to an extent, inherent scientific conservatism.

The final explanation I’d like to raise here is of causal attribution, also related to cognitive biases. The late Professor Tony McMichael coined the term “prisoners of the proximate” to encourage his epidemiological colleagues to think more deeply about cause. Of course, Tony was not the first to do this; causal theory is as old as philosophy. However, despite this vintage, many people, including scientists, get stuck with their preconceptions, and many have trouble conceding not only that there may be additional causal factors, but that these may co-exist with, rather than supplant their current causal preference. This tension is obvious concerning conflict. Military theorists are happy to conceive climate change as a “risk multiplier” for conflict, but not (yet) political scientists.

Climate change can indeed be conceptualised as the most important risk to health this century, but it is only one element in a risky milieu. Lowering the risk from climate change requires reducing the risk of many of its co-determinants of civilisation health. Among these, the most important factor may be complacency.