Over half of known human pathogenic diseases can be aggravated by climate change

Abstract

It is relatively well accepted that climate change can affect human pathogenic diseases; however, the full extent of this risk remains poorly quantified. Here we carried out a systematic search for empirical examples about the impacts of ten climatic hazards sensitive to greenhouse gas (GHG) emissions on each known human pathogenic disease. We found that 58% (that is, 218 out of 375) of infectious diseases confronted by humanity worldwide have been at some point aggravated by climatic hazards; 16% were at times diminished. Empirical cases revealed 1,006 unique pathways in which climatic hazards, via different transmission types, led to pathogenic diseases. The human pathogenic diseases and transmission pathways aggravated by climatic hazards are too numerous for comprehensive societal adaptations, highlighting the urgent need to work at the source of the problem: reducing GHG emissions.

Keywords: Ecology; Environmental health; Environmental impact; Social sciences.

Fig. 1. Climatic hazards of the Earth’s system affected by the ongoing emission of GHGs.

We considered the following ten climate hazards. GHGs mediate the balance between incoming solar radiation and outgoing infrared radiation; thus, (1) their excess in the atmosphere causes warming. Compounded with an increased capacity of the air to hold water, warming accelerates soil water evaporation, leading to (2) drought in places that are commonly dry; excess drought can lead to (3) heatwaves when heat transfer from water evaporation ceases. Drought and heatwaves ripen the conditions for (4) wildfires. In moist places, the quick replenishment of evaporation strengthens (5) precipitation, which is prone to cause (6) floods as rain falls on moist places/saturated soils. Warming of the oceans enhances evaporation and wind speeds, intensifying downpours and the strength of (7) storms, whose surges can be aggravated by (8) sea level rise, which in turn can aggravate the impacts of floods. Uptake of CO₂ in the oceans causes ocean acidification, whereas changes in ocean circulation and warming reduces oxygen concentration in seawater; these combined ocean physical–chemical changes are referred to as (9) ocean climate change in this paper. We included (10) changes in natural land cover as one of the hazards because it can be a direct emitter of GHGs via deforestation and respiration, modify temperature via albedo and evapotranspiration and because it can be a direct modifier in the transmission of pathogenic diseases^,. This figure is intended as a justification for the hazards used and not as a full array of interactions between GHGs and hazards and feedback loops among hazards.

Fig. 2. Literature search strategy.

We carried out three complementary literature searches about case examples of diseases affected by climatic hazards. Search 1 combined as keywords ‘disease’ by each of the ten climatic hazards analysed. Search 2 combined each of the ten climatic hazards analysed by each disease name listed in two authoritative databases of infectious diseases [i.e., GIDEON (Global Infectious Disease and Epidemiology Network) and CDC (Center for Disease Control and Prevention)]. Search 3 was a data gap confirmation, and in it, we looked for all combinations (disease names by climatic hazards) in which the first two searches did not return any case example, using alternative names of the diseases, pathogens and hazards. For this latest search, an approximation of the number of references scrutinized cannot be calculated because this latter search was variable in the number of papers scrutinized until data were found or 200 citations reviewed (Methods).

Fig. 3. Pathogenic diseases aggravated by climatic hazards.

Here we display the pathways in which climatic hazards, via specific transmission types, result in the aggravation of specific pathogenic diseases. The thickness of the lines is proportional to the number of unique pathogenic diseases. The colour gradient indicates the proportional quantity of diseases, with darker colours representing larger quantities and lighter colours representing fewer. Numbers at each node are indicative of the number of unique pathogenic diseases (caveats in Supplementary Information 1). An interactive display of the pathways and the underlying data are available at https://camilo-mora.github.io/Diseases/. Several disease names were abbreviated to optimize the use of space in the figure; their extended names are provided in Supplementary Table 1. Credits: word clouds, WordArt.com; bacteria, Wikimedia Commons (www.scientificanimations.com); other images, istockphoto.

Fig. 4. Diseases affected by climatic hazards.

a, Discrimination of pathogenic diseases between those aggravated and diminished by climatic hazards. b, Set of diseases aggravated by climatic hazards in comparison to all reported ‘infectious’ diseases known to have affected humanity (that is, an authoritative compilation of diseases known to have affected humanity in recent history by GIDEON and CDC; Methods).