Climate change, health and categories of effects

 

I wrote this for another paper, currently under review. However, it was cut, due to lack of space. Eventually, I hope to weave this material into another article, and also into the forthcoming second edition of my edited book “Climate Change and Global Health”. This also builds on a blog I posted in 2015 called “Climate change and heath: primary, secondary and tertiary effects.

1. Primary and secondary effects

The first categorizations of the health effects of climate change and health appeared in the early 1990s. Principally these identified two broad kinds of effect, most often called “direct” (such as from heatwaves, reduced cold or physical trauma from a more powerful storm) and “indirect”, such as from ecological shifts leading to an altered distribution of vectors (such as mosquitoes) or of food sources (see tables 1,2).

Table 1. There are many classifications of the health effects of climate change. This is one suggestion for the most obvious, least contentious effects. All of these effects interact with other factors, such as governance, infrastructure, technology and economic and other capabilities.

Heat stress, heat stroke (including occupational); heat stress resulting in impairment of chronic diseases (e.g. multiple sclerosis, cardiac or renal failure) or death, possible fetal abnormalities; in some cases improved health from reduced cold

Physical and or psychological harm and trauma from an intensified storm, flood, fire or other extreme event, such as drought or a storm surge

Long-lasting psychosocial effects from exposure to a climate change aggravated extreme event including post traumatic stress disorder, depression, loss of place and “solastalgia” ------------------------------------------------------------------------------------------------------------------

The burden of disease of “direct” (“primary”) effects can be severe, as with the tens of thousands of excess deaths attributed to heatwaves in France in 2003 [1] and Russia in 2010 [2]. The burden from excessive heat is likely to substantially increase, especially if the Paris commitments are not met. Regions in which hundreds of millions now live are forecast as at risk of large-scale human abandonment late this century, including the North China plain and parts of the Middle East [3,4]. Looking further ahead, if urgent action to slow climate change by accelerating the energy transition is further delayed, substantial regions of the globe could experience wet bulb temperatures of 35 degrees or more, calling into question the habitability of even more some regions [5].

The burden of disease of the secondary effects (see table 2) of climate change, particularly of infectious diseases such as malaria, has long been forecast as significant [6]. However, although it is likely that climate change has increased cases of malaria in some settings, especially in highlands [7] the overall global burden of malaria has declined substantially in recent decades, mostly because of the increased use of insecticide impregnated bednets and more funding [8]. Note however, that such progress has recently stalled, especially in parts of sub-Saharan Africa [9]. I am unaware of any recent attempts to estimate the global burden of disease of malaria or other infectious diseases attributable in part to climate change, although a recent editorial in Geospatial Health provides an excellent summary of the key issues [10].

Table 2. Climate change has many less direct effects, which can be called “secondary”. Few if any of these are controversial. These effects also interact with other factors, such as ecological change, governance, trade, infrastructure, technology and economic and other capabilities.

Vector borne diseases (eg malaria, dengue fever, yellow fever, chikungunya, Zika), non-vector born zoonotic disease (e.g. schistosomiasis, Ebola, HIV/AIDS); other infectious diseases (e.g. gastro-enteritis, soil transmitted helminthiases)

Impaired food or water safety (microbial or toxic), reduced food diversity; reduced micronutrient concentrations in crops (due to higher CO2 levels)

Allergies, including thunderstorm asthma; asthma

Cardio-respiratory-neurological effects, such as from worsened tropospheric air pollution, or from climate change aggravated fires

Reduced food sovereignty, reduced micronutrient intake, but without the threat of starvation

Impact on other chronic diseases, such as cardiac failure, diabetes ------------------------------------------------------------------------------------------------------------------

2. Tertiary effects

Two papers, each published in December 1993, identified a third category of health effects, which the authors called “tertiary” [11,12] (see table 3). One paper stated “indirect effects are secondary, such as changes in vector-borne diseases or crop production, and tertiary, such as the social and economic impacts of environmental refugees and conflict over fresh water supplies”. The other paper additionally noted that: “There is a considerable literature on the effects of climate on disease which focuses principally on the primary effects of temperature on health. In relation to global climate change, however, it is likely that the secondary and tertiary impacts will outweigh the importance of the primary effects” [12].

This idea of a third major category of health effect has not yet been widely accepted. A 1996 book on climate change and health mentioned “more diffuse” effects including conflict and population displacement, but grouped these with indirect effects, rather than as a separate category [13]. An assessment for the U.S. National Assessment on climate change and health, published in 2000, identified five categories of health outcomes [14]. These were related to temperature, to extreme weather events (storms, tornadoes, hurricanes, and precipitation extremes); to air-pollution, and to two categories of infectious diseases. In turn these were each divided into two kinds; related to water and food, and vectors and rodents. This report did not discuss migration, social disruption, or conflict, perhaps because its scope was restricted to that of the U.S.

As mentioned above, it has long been understood that climate change can influence important social consequences (with health effects) such as population displacement, conflict and malnutrition. Malnutrition refers both to undernutrition (e.g. stunting, wasting and at its most extreme, death) and, also, to obesity and other problems associated with excessive calorie intake, sometimes (also) associated with micronutrient deficiency. Two of these effects (malnutrition – albeit probably meaning undernutrition – and conflict) were mentioned in the the first article I know of about climate change and health, published in the peer reviewed literature, a 1989 editorial in the Lancet [15], while Alexander Leaf, also in 1989, discussed both population displacement and the possibility of increased hunger [16].

These effects may also be considered tertiary not only because they are the least direct, but also because of their capacity to harm health is at such a large scale. For example, the conflict in Syria, which several experts think was contributed to by the most severe drought in its instrumental record [17] has displaced millions, had profound geopolitical effects in Europe, and killed hundreds of thousands of people, including children. The health effects upon survivors, both physical and mental, both in Syria and for those displaced, are undoubtedly immense [18]. Of course, climate change is not solely responsible for this catastrophe, and its exact contribution is disputed [19,20]. The total health impact of the Syrian conflict is likely to far exceed that of the 2003 European heatwave, particularly as much of the health harm to Syrians is to infants, children and young adults, whereas deaths from heatwaves typically result in a comparatively low per person loss of disability adjusted life years, as it is primarily the already frail and elderly who die [21]. The morbidity and mortality from the Syrian conflict due to anthropogenic climate change is likely to already be very significant, even using a highly conservative causal attribution.

It has also been suggested that the 2018 crisis of refugees seeking entry to the U.S. from Central America has been exacerbated by drought (interacting with social and other environmental factors including inequality and high population growth rates), which in turn probably has a climate change contribution [22]. There are many other examples, already, in which climate change has been argued to contribute to conflict, undernutrition, migration and other forms of population displacement [23]. For example, Hurricane Maria, which directly killed 64 people in Puerto Rico, contributed to at least 4,000 additional deaths in the following four months, due in part to the interaction of the storm with an already vulnerable social and physical system, with large-scale and long-lasting damage to electricity infrastructure [24]. It also led to migration to the U.S., particularly by younger people and those more economically able. 

Table 3. This lists the most obvious “tertiary” consequences of climate change that will have significant health effects. As with the primary and secondary effects, these interact with governance, infrastructure, technology and economic and other determinants.

Increased hunger, starvation or famine (exceeding a reduction in nutrient variety)

Mass migration or population displacement, including from climate change aggravated events such as famine, drought, sea level rise, violence and intolerable heat

Large scale conflict (leading to physical and mental trauma, death and morbidity, including from damaged health systems)

Significant social and economic disruption, impairing health and/or health systems ------------------------------------------------------------------------------------------------------------------

In 2005 a paper written by health workers, published outside the health literature, argued that the global health effects of eco-climatic change could be classed into four categories; three equivalent to primary, secondary and tertiary (though the paper did not use these terms), and a fourth, which it called “systems failure”, a euphemism for global civilization collapse [25]. This paper also predicted that the loss in disability adjusted years for the third and fourth categories would exceed the first two.

A figure in a chapter on climate change and health published in 2007 in the third report of the Intergovernmental Panel on Climate Change (IPCC) also recognized three broad categories of health effects. It called these “direct”, “indirect” and via “social and economic disruption” [26]. However, the text did not discuss the third category.

In 2010 the terms (and closely corresponding concepts) of primary, secondary and tertiary were revived, in a paper, and later, an edited book that failed to identify the earlier use of these terms [27,28]. Also in 2010, a report for several U.S. government agencies [29] classified the human health consequences of climate change into eleven kinds. These were listed alphabetically as asthma, allergies and airway diseases; cancer; cardiovascular disease and stroke; alterations in normal development; heat-related morbidity and mortality; mental health and stress disorders; neurological diseases and disorders; nutrition and food-borne illness; vector-borne and zoonotic disease; waterborne disease and weather-related morbidity and mortality. The report discussed displaced people (such as due to Hurricane Katrina) as a cross-cutting issue. It also recognized the possibility of conflict, war (outside the U.S.) and extensive undernutrition, both domestically and globally.

The health chapter in the most recent IPCC report [30] also referred to three kinds of health effects of global warming. It called these “direct” (mainly from “heat, drought, and heavy rain”), “mediated through natural systems” (e.g. “disease vectors, water-borne diseases, and air pollution”) and “heavily mediated by human systems” (e.g. “occupational impacts, undernutrition, and mental stress”). The first two categories in this classification correspond with primary and secondary, but in the third category only large-scale undernutrition would be classed as a tertiary effect, as defined above.

In 2015 another major Lancet report was released [31]. It proposed that impacts can be “direct” (e.g. “heatwaves and extreme weather events such as a storm, forest fire, flood, or drought”) or “indirectly mediated through the effects of climate change on ecosystems economies, and social structure” (e.g. “agricultural losses and changing patterns of disease” and “migration and conflict”). It thus grouped “tertiary” effects with “secondary”, though it used neither term. A figure in that paper which outlined the main direct and indirect effects focused solely on what this essay suggests are more parsimoniously termed as primary and secondary effects.

Conclusion

Apprehension of what I prefer to call the "tertiary" health effects of climate change has always been the primary motivator for my writing and researching on climate change (since my first letter, published in the Medical Journal of Australia, in 1991) [32]. I have argued above that these potential aspects were apparent in 1989, when articles first appeared mentioning all major "tertiary" components. I have also shown that the term "tertiary" was introduced in two papers published in 1993, already a quarter of a century ago. 

Although there is increased recognition of these risks, the vast majority of the climate change and health literature continues to focus on issues such as heat, infectious diseases and allergies. Important as these issues are - and they are certainly are valid - I believe that their future burden of disease is likely to be dwarfed by that of the tertiary issues; conflict, population displacement and famine. 

In 2014, in a chapter in my edited book called "Mental health, cognition and the challenge of climate change [33] I published a version of the following figure. In the next issue of the book the figure may be adapted, so that the label for the x axis (the horizontal axis) reads 2030. In 2014 I suggested that it might take until 2050 for the high burden of disease of the tertiary effects to be accepted, but that book was drafted before as much was reported about climate change and conflict in Syria, although an early paper was published in 2014 [34}.

I fear, given the events of 2018 - the fires, the floods, the hurricanes and typhoons, and the ongoing population displacement, as well as a gradually increasing acceptance of the role climate change plays in conflict - that the time in which the overwhelming risk of the tertiary health effects of climate will be widely understood may well be before 2050.  On the other hand, the vast majority of articles in the climate and health field continue to completely ignore its existential risk [35].

The proportional burden of disease of primary, secondary and tertiary effects (averaged over the 21st century) and the approximate time when these concepts and their relative burdens are accepted.

A powerful opposing force, however, is not just denial, nor just the political factors that seek to repress any whiff of legal liability, and hence minimize the risk of future reparations. One way to suppress such exploration is to refuse to fund research into the possible links. I think another reason has evolutionary roots. People like to portray themselves as “good", even moral. Even the Nazis probably did .. so while on one hand populations fully support policies that contribute to unspeakable misery, on the other hand they deny the reality of the links between their behaviour and the more displaced effects, especially if they are harmful. If the causes can be ascribed elsewhere ("local politics in Syria, not environment") then we can feel better about ourselves. A good example is that most Australians support offshore camps for asylum seekers, claiming this is “humane” because “it saves lives at sea”.  However, my view is that the causation of this and other tertiary effects is multi-factorial. Developed countries have largely contributed to climate change, but there are also many local factors that have contributed to the war, famine, displacement, and the risks people take which see some drown at sea.  

 

However, the  pendulum on the causes of the tertiary effects of climate change is currently too remote from recognition of the role that high-income countries have played in these catastrophes [36}, already and in future. And some people increasingly understand that climate change and other forms of planetary overload [37] pose profound risks to human well-being in high-income settings, such as 15 year old Swedish climate activist Greta Thunberg, who also keenly appreciates the equity dimension (see figure).

A tweet from 15 year old Greta Thurnberg, posted October 7, 2018

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