Role of climate
change in health
Nutritional Studies 5
What is climate change?
• Climate change = long-term shifts in temperatures and weather patterns
• Shifts may be natural e.g., variations in the solar cycle, volcanic eruptions, ocean currents,
the earth's orbital changes
• Earliest assumptions about the greenhouse effect - Jacques Fournier back to 1824
• But since the 1800s - human activities main driver of climate change – primarily by:
• burning fossil fuels e.g., coal, oil and gas,
• heating of buildings,
• methane emissions from livestock
• clearing land and forests release CO2, less plants to absorb CO2
• landfills for waste are a major source of methane emissions
• electricity generation
• coal mining, chemical reactions for making cement, steel, aluminum, and fertilizer etc.
• Burning fossil fuels etc. - generates greenhouse gas emissions - act like a blanket
wrapped around the earth, trapping the sun’s heat and raising temperatures
Greenhouse effect
• Greenhouse gasses causing climate change - carbon dioxide (CO2) and methane (CH4)
• Global greenhouse gas emissions in 2019 - 59 billion tonnes of CO2
• Of these emissions, 75% CO2, 18% CH4, 4% nitrous oxide, and 2% fluorinated gases
Greenhouse effect
• Greenhouse gas concentrations are at their highest levels in 2 million years
• Ever increasing - earth is 1.1°C warmer than late 1800s
• Last decade (2011-2020) - warmest on record
• Average temperature could be between 1.1 to 5.4°C warmer by 2100
• Result:
• deserts expanding, less land for agriculture, more invasive pest outbreaks
• heat waves and wildfires more common
• warming of the Arctic - glacial retreat and sea ice loss
• higher temperatures – more intense storms, droughts + weather extremes
• rapid environmental change in mountains, coral reefs + the Arctic - forcing
many species to relocate or become extinct
• food and water scarcity - increased flooding, extreme heat, more disease,
and economic loss
• WHO calls climate change the greatest threat to global health
in the 21st century
Greenhouse emissions
by country
South Africa: CO2 emissions 2019 (Mt): 433.60, CO2 per capita 2019 (tons): 7.4
Total GHG emissions 2018 (kilotons): 513,440
Effects of climate change
• We are already experiencing the repercussions of climate change
• Without mitigation and adaptation - impacts will intensify over time
• Presents unique challenges to the world's ability to meet health, food security and nutrition
needs
• Food systems highly sensitive to climate
• Future effects of climate change - most evident among sub-Saharan Africa and South and
Southeast Asia
• Many people – live in rural areas and experience poverty
• Livelihoods severely affected
• Many of the systems engage with e.g., health, education, and food systems - significantly affected by climate
change.
Versus
South Africa
• Modelled projections indicate that warming over southern Africa is happening at twice the
global rate
• Unless international action is taken to reduce greenhouse gas emissions:
• temperatures may rise more than 4 °C over the southern African interior by 2100
• increases of more than 6 °C over the western, central and northern parts of the country are expected
• Relative to the 1981–2000 period – possibility of summer heat waves over South Africa
increased by over 3.5 fold
• Climate change poses a significant threat to South Africa's water resources, food security,
health, infrastructure and ecosystem services and biodiversity
• South Africa contributes considerable CO2 emissions - 14th largest emitter of CO2
• Per capita emissions, above the global average
• Energy system relying heavily on coal and oil
Greenhouse effect
• Climate change, agriculture, and nutrition are interconnected
• Climate change and variability affects temperature and rain + frequency and severity of
extreme weather events.
• Increases in temperature, heat waves, and droughts - impact agriculture - decreased crop
yields and livestock productivity, declines in fisheries and agroforestry
• Climate change affect food quality (diversity, nutrient density, and safety) and food prices
• Implications for health, food security, human diets and nutrition
• Climate change affects the ability to move food from production to markets, access to
diverse, high-quality diets become more limited.
• Reduced access to sufficient nutrient-dense foods - impaired nutritional status and
diminished resiliency, particularly in low-income communities
Direct health effects
• Analysis of data over the past 17 years - temperature-related mortality (from cold or hot
spells) accounts for 3.4% of deaths in South Africa
• Extremes of age are most vulnerable
• given their reduced thermoregulatory ability,
• more limited mobility and resources to adjust to extreme temperatures.
• Data from Cape Town, Durban and Johannesburg - for every 1°C rise, overall mortality
escalates by 1% - 2% in those aged above 65 years
• Heat exposures – particularly dangerous in pregnant women and the developing foetus more likely to get heat exhaustion or heat stroke
• South African mine workers - mortality rate of 3.3 deaths/year/1000 miners if the
temperature exceeded 34°C, compared to 0.7 deaths/year/1000 miners when temperatures
are between 31°C and 33°C
• Informal settlements – houses made of sheets of corrugated iron, bricks, wood and plastic poorly insulated against heat and cold.
• Hot weather 4–5°C warmer than outdoor temperatures and cooler during cold spells by the same magnitude
• Brick and cement offer better insulation against extreme temperatures
• Same apply to schools and public health facilities
Indirect health effects
Infectious diseases
• Transmission of vector-borne diseases (infections transmitted by the bite of infected insects)
• Rises in temperature + rain - linked with malaria spikes, especially in Limpopo
• These spikes often occur around two months after warmer temperatures and high precipitation have occurred
in neighbouring countries
• Rift Valley Fever - mostly affects the semi-desert Karoo - acute viral hemorrhagic fever domesticated animals e.g. cattle, sheep, goats - can also cause illness in people.
• Changes in the distribution of mosquito species - ↑ transmission of dengue fever, Zika and
other infections in SA.
• Zika infection – pregnant women - microcephaly
• The Avian influenza (bird flu) epidemic in South Africa in 2017, attributed, in part, to climate
change - threatens poultry food sources
• Global warming may alter the distribution, breeding and survival of snail species implicated
in schistosomiasis (bilharzia - infection caused by a parasitic worm that lives in fresh water) –
snails habitat = highly sensitive to water temperature.
Indirect health effects
Water and food borne pathogens
• Droughts and high precipitation worsen water quality - hamper hand washing and other
hygiene practices.
• Bacterial pathogens multiply faster in higher temperatures - can result in breakdowns in
food cooling chains.
• Study in children <5 years in Cape Town - 5 °C rise in minimum weekly temperatures
increased cases of diarrhoea by 40%.
• Escalation in sea-surface temperature - linked to a cholera outbreak in 2000–2001 in
KwaZulu-Natal - stemming from ↑abundance of phytoplankton - ↑small crustaceans
(cholera lives in symbiosis with crustaceans in their intestines) that feed on these organisms
• Listeria monocytogenes (listerioses), 2017 major epidemic across South Africa - particularly
climate sensitive, with occurrences rising with temperature spikes
• In food processing plants - water scarcity hampers efforts to clean food-processing machines
Indirect health effects
Impact on specific population groups
• Extreme impact - who depend on climate-sensitive resources and ecosystems for livelihoods.
• Soil drying + irregular rainfall caused by rising temperatures especially western regions of South
Africa - constrains agricultural production
• Most harmful for subsistence farming communities - already prone to geopolitical and economic marginalization
• Rainfall shortage + ↑temperatures + ↓soil moisture - associated with internal migration in the country
• Especially true for communities highly dependent on natural resources for livelihood (e.g., firewood, seeds and wild
foods)
• Movement to inner-city areas + informal settlements – very concerning as these areas have the
highest risks of HIV transmission
• Known as eco-migration - accentuate the already high levels of urbanization in SA
• Migration - ↑risks of sexual violence for women - some female migrants may have few options
for survival other than sex work
• Eco-migration erodes social networks – practical + emotional resources underpinning health
and well-being
• Migration related to climate change ↑xenophobic attitudes → generate conflict and violence
Indirect health effects
Type 2 diabetes
• Biological relationship - brown adipose tissue (BAT) - activated in a cold environment
• Responsible for combusting lipids + stimulate sympathetic nervous system to generate heat
• ↑ lipid usage by BAT - ↑ influx of glucose to skeletal muscles → improve insulin sensitivity
• Studies indicated inverse relationship between high BAT activity and blood glucose + HbA1c levels following
a cold exposure, independent of body fat
• Effect suppressed during hot weather
• Incidence rate of obesity-adjusted diabetes ↑ by 0.295% per 1 000 for every °C ↑, while
diabetes prevalence increases by 0.170% for every °C ↑
• Type 2 diabetes - more prone to an impaired orthostatic response in high temperatures impaired bodily thermoregulation
• During heat waves + hot weather – more frequent emergencies and hospitalisations
• More prone to dehydration and heatstroke than non-diabetic individuals
• Predisposed to CVD events including myocardial infarction in high air pollution and during
heat waves.
• Furthermore, the stability and kinetics of exogenous insulin - altered in high temperatures.
Cuschieri and Agius (2021)
Indirect health effects
Effect of heat stress on the kidney
• Extreme heat can cause heat stroke – hyperthermia >40.6°C - delirium, coma, seizures, and
multiorgan failure
• Acute kidney injury – common in heat stroke – 10-30% persons with heat stroke-associated
acute kidney injury require dialysis - some cases of heatstroke may progress to CKD
• Kidney stones (nephrolithiasis) - heat stress + dehydration predispose to urinary
concentration and low urine volumes that increase the risk for stone formation
• UTIs also related to underhydration and potentially affected by climate change
• Soft drinks containing fructose - local tubular injury, inflammation, and oxidative stress
when metabolized by the kidney
• Soft drinks may increase the risk for acute and chronic kidney injury
• Experimental studies have shown that rehydration with soft drinks
could enhance kidney damage in dehydrated rats
• Rehydration with soft drinks could induce markers of kidney damage
in healthy subjects following exercise in high temperatures
Indirect health effects
Allergies
• Well documented - climate change leads to worsening symptoms in people with allergic
disease
• People with chronic respiratory allergic disease e.g., asthma and allergic rhinoconjunctivitis
at particular risk due to increased exposure to pollen + increased concentration and
distribution of air pollutants
• Climate change increase intensity + duration of pollen season
• ↑ in CO2 - lead to a reflexive increase in plant reproduction and total pollen levels
• As CO2 concentrations ↑ so do plant species that thrive at high CO2 concentrations
• Climate change – linked to ↑ concentrations and distribution of air pollutants e.g., O3, NO +
other volatile organic chemicals
• Inhalation of air pollutants e.g., diesel exhaust particles (DEP), SO2 and NO2 cause
inflammation + ↑ mucosal permeability within the airways - ↑ barrier penetrance by
allergens
• Oxidative stress - oxidants produced by pollutants within respiratory mucosal epithelial cells
trigger the release of inflammatory mediators → destruction and apoptosis of respiratory
mucosal cells → bronchial hyperreactivity
• In addition to ↑ mucosal permeability, DEPs can bind to pollens, animal and other allergens,
directly facilitating their entry into the respiratory epithelium
Indirect health effects
Microbiota
• Human GIT microbiota – consist of 100 trillion microbes from at least 160 different species
• Bacteria - active role in human immunity – dysbiosis → development of infectious,
inflammatory and autoimmune disease
• Dysbiosis related to plant biodiversity - nearly 1 million animal and plant species are
threatened with extinction as a result of climate change - with a decline in macro-diversity
comes a decline in micro-diversity
• “biodiversity hypothesis” suggests - reduced contact between people and a biologically
diverse natural environment adversely affect the microbiota and its immunomodulatory
capacity
• Clear link between microbiome composition, diet and lifestyle habits – fruit, vegetables,
dietary fiber, fermented foods, excess use of antibiotics
Indirect health effects
Most vulnerable groups
• Strongest evidence for older age (age >65 years)
• Vulnerability partly attributable to comorbidities, use of medications, and a decline in
thermoregulatory function e.g., reduced skin blood flow and sweat rate
• Underlying medical conditions e.g., CVD, lung diseases, diabetes, neurodegenerative
diseases (Alzheimer’s and Parkinson’s disease), mental health issues - greater vulnerability
to heat stress
• Pregnant women - ↑risk during heat exposure due to ↑heat production:
• Result of body weight gain + metabolic demands of the growing foetus
• more susceptible to dehydration
• risk factor for adverse birth outcomes, including preterm birth, low birth weight, stillbirths, and congenital
heart defects
• Occupational settings → prolonged heat exposure and intensive physical work - more heat
stress for workers, even at temperatures lower than those that trigger heatwave alerts
• Mines, hot kitchens, seasonal farm workers, military personnel
• Occupational heat strain needs to be recognised when assessing the heat-related risk of
workers