2.2.6.4 Health

Crossing climate system tipping points could lead to an increase in the frequency and intensity of extreme weather events such as heatwaves, hurricanes, floods and droughts (Heinze et al., 2021; Schellnhuber and Martin, 2014). More frequent and intense heatwaves can lead to heat-related illnesses, such as heat exhaustion and heatstroke (Sorensen and Hess, 2022), while high temperatures can also worsen existing health conditions, such as cardiovascular and respiratory diseases (Covert et al., 2023). Severe storms and flooding, for example due to AMOC collapse (Jackson et al., 2015) can directly cause injuries and deaths as well as displacement, and damage to infrastructure (Lane et al., 2013).

As discussed in Chapter 2.2.6.1, fresh water sources and water security would be perturbed significantly by crossing tipping points such as AMOC collapse and in the cryosphere. Reduced rainfall and increased evaporation can result in water scarcity, making it challenging for communities to access safe and sufficient drinking water, especially in the Global South (Dos Santos et al., 2017). Changes in precipitation patterns and flooding events can contaminate water sources and increase the risk of waterborne diseases such as cholera and gastrointestinal infections (Nichols et al., 2018) and lack of access to clean water and proper sanitation can also contribute to the spread of disease (WHO, 2011).

Biogeophysical tipping points could potentially disrupt agricultural systems and lead to crop failures and reduced yields (Defrance et al., 2017), resulting in possible food shortages and increased food prices (d’Amour et al., 2016) and malnutrition, especially in developing nations (Pawlak et al., 2020). Inadequate nutrition can weaken immune systems, making populations more susceptible to infections and diseases (Calder, 2021).

Wildfires due to Amazon and boreal forest dieback may result in hazardous air quality, exposing populations to smoke and particulate matter (Chen et al., 2021; Cascio, 2018), which can worsen respiratory conditions (Alahmad et al., 2023; Chen et al., 2021). Amazon forest loss is also projected to increase the risk of heat stress. In a climate model simulation reaching approximately 2.5°C by 2100, total conversion of forest to savannah would expose approximately 6 million people to extreme heat stress risks from Wet Bulb Globe Temperatures above 34°C, at present population levels (de Oliviera at al,. 2021).

Climate change and ecological disruptions can alter the distribution and behaviour of disease vectors and reservoirs, potentially facilitating the spread of infectious diseases to new areas (Nova et al., 2022). Climate change-induced shifts in temperature and precipitation patterns can influence the distribution and transmission of vector-borne diseases like malaria, dengue fever, Zika virus and Lyme disease (Beermann et al., 2023; Fox et al., 2015), these climatic patterns can be shifted due to tipping points. Accelerated melting of the Greenland Ice Sheet could impact malaria distribution in Africa through cooling and shifts in precipitation. This could result in a moderation of the increase in malaria risk in East Africa and an increased risk in southern Africa (Chemison et al., 2021). Expanding geographic ranges of disease-carrying vectors can expose new populations to these diseases (Caminda et al., 2019). There is also concern that future warming and increased glacier melting would make disease emergence more likely in the High Arctic region due to  ‘viral spillovers’, by creating new associations and increasing the likelihood of contact between viruses and their animal, plant or fungal hosts (Lemieux et al., 2022).

Rising sea levels may also impact upon the spread of diseases locally during inundation of low-lying areas (Dvorak et al., 2018; Ramasamy and Surendran, 2011). Examples include vector-borne infectious diseases, with the expansion of shallow low-lying brackish and saline environments providing breeding sites for mosquitos and increasing the prevalence of vector-borne diseases such as malaria (Ramasamy and Surendran, 2011). Risks from these could be realised sooner, and happen at a faster pace than adaptation can respond to, in the event of extreme sea level rise caused by ice-sheet disintegration. 

Lastly, the health impact due to various sectors discussed above would have consequences on the decision making of migration/settlement abandonment due to perception of climate risks (McLeman et al., 2011), especially when amplified by the likelihood of crossing tipping points. Displacement can lead to overcrowded living conditions and increased vulnerability to certain transmissive health risks (Suhrcke et al., 2011). Increased climate-related health impacts can place additional strain on healthcare systems, especially in regions already facing resource limitations (Salas et al., 2019; Ebi et al., 2021). 

The disruption to community (see also Chapter 2.2.6.5) will also further exacerbate the health risks, especially related to mental health (Simpson et al., 2011). Studies have shown population displacement and loss of livelihoods can have significant psychological effects on individuals and communities, including increased stress, anxiety and trauma-related disorders (Siriwardhana and Stewart, 2013; Math et al., 2015; Garry and Checchi, 2020). In addition, there are wider climate change-related mental health concerns (Charlson et al., 2021; Palinkas and Wong, 2020) relating to acute (e.g. hurricanes, floods, wildfires) and subacute events (e.g. drought, heat stress) as well as long-term changes (e.g. a permanently altered and potentially uninhabitable environment; see also Chapter 2.5.3.4).