Health Effects of Climate Change

Slide 1 · Health Effects of Climate Change

Environmental mechanisms and their human health consequences

Greenhouse gases → changing hazards → disease

A clinicopathologic framework

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Explain how greenhouse gases alter climate and environmental exposures.

Trace direct and indirect pathways from climatic hazards to human disease.

Compare heat-, water-, vector-, air-, and food-related health effects.

Explain displacement, vulnerability and the rationale for mitigation.

Slide 3 · Environmental disease has multiple origins

Personal environment

1. Behavior-related exposures

2. Diet and substance use

3. Factors acting on individuals

Ambient environment

1. Air, water and surrounding climate

2. Physical and chemical hazards

3. Exposures shared across populations

Climate change shifts the ambient conditions in which many diseases develop.

Slide 4 · Climate hazards become health outcomes

Changing climate

Environmental exposure

Pathophysiologic burden

Disease / injury

A climate signal becomes a health effect through a specific exposure pathway.

Causal sequence (schematic)

Slide 5 · Three levels of climate–health causation

Drivers

Greenhouse-gas accumulation and reduced plant carbon fixation.

Hazards

Extreme heat, severe weather, air pollution and water disruption.

Outcomes

Injury, infection, cardiopulmonary disease and malnutrition.

Slide 6 · Documenting warming in the reference period

1.18°C

2023 global land–ocean anomaly

A 2023 temperature 1.18°C above the twentieth-century average.

Historical textbook measurement; Not a current-year figure.

Slide 7 · Climate and weather are different scales

Climate change concerns sustained shifts in conditions, not a single event.

Extreme weather represents one pathway through which altered climate affects health.

Warming trends, changing precipitation extremes and ice loss.

Slide 8 · Physical consequences of a warming planet

Heat

More severe thermal exposure

Storms

Changing frequency and severity

Water

Drought and flooding

Ice

Loss of land and sea ice

Slide 9 · A warming ocean affects coastal risk

Rising ocean temperature

Thermal expansion

Higher sea level

Coastal exposure

Thermal expansion operates alongside meltwater from land-based ice.

Causal sequence (schematic)

Slide 10 · Ice loss has two distinct implications

Land-based glacial ice

1. Melting contributes water to the oceans.

2. Greenland and Antarctica are cited as major ice-loss regions.

Arctic Ocean sea ice

1. The source describes dramatic thinning and disappearance.

2. Its loss documents climatic change; Distinguish from land-ice addition to sea level.

Slide 11 · Greenhouse gases alter energy balance

Solar energy enters

Earth radiates energy

Greenhouse gases absorb radiation

Less energy escapes

Atmospheric heat retention underlies the greenhouse effect.

Causal sequence (schematic)

Slide 12 · Principal greenhouse constituents named by Robbins

Carbon dioxide

Emissions from fossil fuels

Methane

A greenhouse gas

Ozone

Also a clinically important air pollutant

Water vapor

Participates in heat trapping

Slide 13 · Fossil fuel combustion increases CO₂

Fossil fuel burning

CO₂ released

Atmospheric CO₂ rises

Greenhouse warming

Combustion-derived carbon dioxide as a central driver.

Causal sequence (schematic)

Slide 14 · Deforestation amplifies atmospheric CO₂

Tree cover reduced

Carbon fixation declines

CO₂ removal falls

Atmospheric burden rises

Atmospheric concentration reflects both emissions and biological removal.

Causal sequence (schematic)

Slide 15 · Two complementary routes to higher CO₂

Increased source

1. Burning fossil fuels releases CO₂.

2. Higher emissions add carbon to the atmosphere.

Reduced sink

1. Deforestation reduces plant uptake.

2. Lower carbon fixation leaves more CO₂ in the atmosphere.

Climate intervention may address sources and sinks through different mechanisms.

Slide 16 · Atmospheric CO₂: Reference values

419.3 ppm

Annual average reported for 2023

The section contrasts this concentration with an approximately 280 ppm preindustrial level.

Both figures are reported by the textbook; No updated measurement is implied.

Slide 17 · Observation is not the same as projection

Observed / reported

1. 2023 temperature anomaly

2. 2023 atmospheric CO₂ concentration

3. Reported sea-level change since 1900

Projected / conditional

1. Future warming under model assumptions

2. Future crop losses in some settings

3. Future sea-level and health burdens

Future estimates depend on the emission pathway, exposure and adaptation.

Slide 18 · Why health outcomes vary

Magnitude of change

Speed of change

Hazard severity

Capacity to mitigate

Robbins frames health consequences as conditional rather than fixed.

Causal sequence (schematic)

Slide 19 · The principal exposure pathways

Thermal

Heat and severe weather

Air

Pollution and allergens

Biologic

Vectors and microbes

Systems

Water, crops and displacement

Slide 20 · Direct, ecological and societal impacts

Direct exposure

Heat illness; Injuries during severe weather.

Ecologic change

Vector ranges, contaminants, allergens and food supply.

Societal cascade

Migration, disrupted livelihoods and poverty.

Slide 21 · From environmental factor to clinical consequence

Environmental change

Health pathway

Examples

Extreme heat

Thermal / circulatory stress

Heat illness, cardiovascular failure

Air pollution

Respiratory / cardiovascular burden

Asthma, cardiovascular disease

Water contamination

Enteric infection

Cholera, diarrheal disease

Food disruption

Reduced dietary access

Malnutrition

Slide 22 · Multiple hazards may converge in one patient

Heat + poor air quality

Cardiopulmonary strain

Illness exacerbation

Excess morbidity

The pathways are not independent: Co-exposure can occur during one climate event.

Causal sequence (schematic)

Slide 23 · Direct pathway: Extreme heat

Extreme heat

Human thermal exposure

Heat-related illness

Illness and death

The source explicitly identifies heat-related illness and mortality.

Causal sequence (schematic)

Slide 24 · Heat exacerbates vascular and cardiac disease

Heat waves to increased cardiovascular and cerebrovascular disease burden.

The accompanying climate–health figure includes cardiovascular failure among heat-associated outcomes.

Existing disease burden matters when evaluating vulnerability to a heat event.

Slide 25 · Cardiovascular vs cerebrovascular effects

Cardiovascular

1. Exacerbation of cardiac disease during heat waves.

2. Cardiovascular failure appears among the described consequences.

Cerebrovascular

1. Heat waves are described as worsening cerebrovascular disease.

2. Interpret as a reported health association, not a disease-specific diagnostic criterion.

These are related but distinct disease categories.

Slide 26 · Heat and respiratory illness can coexist

Thermal exposure

1. Extreme heat has direct physiologic consequences.

2. Heat-related illness and death are explicitly listed.

Respiratory co-exposure

1. Heat waves may occur alongside air pollution.

2. Aggravated respiratory disease as a major outcome.

Slide 27 · Clinical consequences of heat exposure

Pathway

Outcomes named in Robbins

Interpretive point

Direct heat

Heat-related illness; death

Potentially life-threatening exposure

Cardiac

Cardiovascular disease / failure

Exacerbation during heat waves

Cerebral vascular

Cerebrovascular disease

Heat-associated disease burden

Respiratory co-exposure

Respiratory disease

Pollution may add risk

Slide 28 · Storms produce immediate and delayed harms

Severe weather

Physical danger

Injury / fatality

Psychological effects

Robbins Fig. 9.2 includes injuries, fatalities and mental-health impacts.

Causal sequence (schematic)

Slide 29 · Disaster pathways are clinically distinct

Immediate

Trauma, injury and deaths linked to storms.

Infrastructure

Damage to safe water and sewage systems.

Longer-term

Displacement and mental-health impacts.

Slide 30 · Flooding disrupts sanitation barriers

Heavy rain / flood

Water and sewage disruption

Contamination

Enteric infection

A flood need not infect directly: Damaged sanitation enables transmission.

Causal sequence (schematic)

Slide 31 · Hazard versus secondary disease

Primary hazard

1. Flooding, storms and physical damage.

2. Injuries and immediate mortality.

Secondary consequences

1. Contaminated drinking water or food.

2. Subsequent gastroenteritis or cholera.

The causal sequence determines prevention priorities.

Slide 32 · Wildfire-related pollution affects health

Changing wildfire burden

Air pollution exposure

Cardiorespiratory stress

Disease exacerbation

The section connects wildfire-related pollution with cardiovascular and respiratory harm.

Causal sequence (schematic)

Slide 33 · Air pollution reaches several disease systems

Pulmonary effects

1. Asthma and respiratory disease are named outcomes.

2. Air pollution is one component of the broader climate–health chain.

Cardiovascular effects

1. Cardiovascular disease is also associated with climate-related air pollution.

2. Do not restrict the health effect of poor air quality to the lungs.

Slide 34 · Climate-linked allergens: A separate pathway

Climatic / environmental shift

Increasing allergens

Allergic airway exposure

Respiratory allergies / asthma

The source figure identifies respiratory allergies and asthma as downstream outcomes.

Causal sequence (schematic)

Slide 35 · Pollutants and allergens are not synonyms

Air pollution pathway

1. Ozone and wildfire-related pollution are emphasized.

2. Cardiovascular and respiratory outcomes.

Increasing allergen pathway

1. Allergic exposures are separately displayed.

2. Respiratory allergy and asthma outcomes.

Both can affect asthma; Their upstream exposures differ.

Slide 36 · Climate affects safe water access

Extreme rainfall / disaster

Water-system damage

Microbial contamination

Human exposure

The infectious consequence depends on breakdown of clean water and sanitation.

Causal sequence (schematic)

Slide 37 · Water-related conditions Fig. 9.2

Condition / agent

Category

Common exposure link

Cholera

Named water-quality outcome

Contaminated water

Cryptosporidiosis

Named water-quality outcome

Contaminated water

Campylobacter infection

Named water-quality outcome

Food / water

Leptospirosis

Named water-quality outcome

Water-quality disruption

Harmful algal blooms

Environmental water hazard

Water quality degradation

Slide 38 · Waterborne and foodborne disease pathways

Waterborne

1. Drinking water becomes contaminated.

2. Water infrastructure is disrupted by flooding.

Foodborne

1. Contaminated food transmits enteric pathogens.

2. Disasters can compromise safe food handling and supply.

Robbins groups both pathways as infectious consequences of altered climate.

Slide 39 · Gastroenteritis is a population-level outcome

Floods and heavy rains can disrupt clean water supplies.

Sewage-treatment disruption increases the opportunity for contamination.

The downstream disease burden includes gastroenteritis and cholera.

Slide 40 · Vector ecology translates climate into infection

Temperature / weather shift

Vector ecology changes

Exposure patterns change

Vector-borne infection

Vector number and geographic distribution are explicit mediators.

Causal sequence (schematic)

Slide 41 · Vector number and vector range are distinct

Vector abundance

1. Changes in vector number can alter opportunities for transmission.

2. Transmission risk is not determined by climate alone.

Geographic distribution

1. Changes in where vectors occur can expose different populations.

2. Location of risk may change even without a uniform global increase.

Slide 42 · Vector-associated diseases named

Examples explicitly listed

Grouping for teaching

Malaria; dengue

Core examples in the chapter narrative

Chikungunya; West Nile virus

Additional arthropod-borne examples from Fig. 9.2

Lyme disease; encephalitis

Illustrative vector-associated outcomes

Rift Valley fever

Additional outcome shown in the source figure

Slide 43 · Weather variability alters vector risk

Temperature changes and extreme weather variation among drivers.

The section cites El Niño events as an example of climatic variability.

It is inappropriate to presume one uniform response across all pathogens or vectors.

Slide 44 · Climate suitability is not a clinical diagnosis

Environmental inference

1. Vector abundance and habitat may change.

2. Geographic exposure may become more plausible.

Clinical confirmation

1. The source does not provide diagnostic tests or criteria.

2. Specific infection still requires ordinary disease-specific evaluation.

Ecologic hazard should not be mistaken for confirmed disease.

Slide 45 · Crop disruption contributes to malnutrition

Local climate changes

Crop production declines

Food availability threatened

Malnutrition risk

This pathway operates through the food system rather than direct heat injury.

Causal sequence (schematic)

Slide 46 · Why tropical cropping systems may be vulnerable

Thermal context

1. Some tropical average temperatures are already near crop tolerance levels.

2. Additional warming may worsen growing conditions.

Health implication

1. Crop disruption threatens the local food supply.

2. Reduced nutritional security can increase malnutrition.

Slide 47 · Illustrative agricultural projection

10–25%

Possible productivity decline by 2080

This projected range for some low-resource countries—not a worldwide observed loss.

Conditional projection; Not a measurement.

Slide 48 · Direct heat injury differs from food insecurity

Direct / rapid

1. Exposure to an extreme temperature.

2. Heat-related illness develops through thermal stress.

Indirect / systemic

1. Changed climate affects crop yields.

2. Food-system disruption contributes to malnutrition.

Different latencies and intermediates require different health responses.

Slide 49 · Water and food pathways interact

Extreme weather

Water / crop disruption

Infection and food insecurity

Health deterioration

Multiple climate mechanisms can affect the same community.

Causal sequence (schematic)

Slide 50 · Two processes raise mean sea level

Ocean warming

Thermal expansion

Higher sea level

Coastal flooding

Land-ice melt also adds ocean water: The processes act together.

Causal sequence (schematic)

Slide 51 · Sea-level change: Observation vs forecast

Historical record in source

1. Approximately 13–20 cm of global mean rise since 1900.

2. Reported as a historical quantity, not an annual rate.

Future possibility in source

1. Substantial additional rise is projected by 2100.

2. Low-lying settlements face varying exposure.

Projection ranges should not be described as already observed.

Slide 52 · Coastal flooding may trigger migration

Rising sea level

Flood / land loss risk

Displacement

Social and health impacts

The downstream impact extends beyond the initial physical hazard.

Causal sequence (schematic)

Slide 53 · Displacement creates layered health risks

Material disruption

Homes, livelihoods and commerce may be lost or interrupted.

Social instability

Poverty, political unrest or conflict may follow.

Health consequences

Malnutrition, illness, death and psychological impacts may increase.

Slide 54 · Low-lying communities face concentrated exposure

People living in low-elevation coastal areas.

Even smaller rises may worsen coastal flooding risks.

The Maldives is used as an example of substantial exposure.

Population vulnerability depends on the ability to adapt or relocate.

Slide 55 · One hazard can affect multiple outcomes

Flood

Injury and waterborne infection

Heat

Cardiopulmonary disease

Drought

Food-system stress

Coastal change

Displacement and poverty

Slide 56 · Clinical outcomes versus transmission routes

Type of consequence

Representative outcome

Dominant pathway

Physical injury

Storm-related trauma

Direct hazard

Thermal illness

Heat-related disease

Direct heat

Infectious

Cholera; malaria

Water or vector ecology

Chronic exacerbation

Asthma; cardiovascular disease

Air / heat

Nutritional / social

Malnutrition; displacement

Food and coastal systems

Slide 57 · Climate burden depends on adaptive capacity

Hazard intensity

Population exposure

Underlying vulnerability

Adaptive response

Similar physical hazards may generate different consequences in different settings.

Causal sequence (schematic)

Slide 58 · Risk is unevenly distributed

Higher vulnerability

1. Low-lying coastal populations.

2. Crop-dependent settings near climatic tolerance limits.

3. Populations lacking robust sanitation or water systems.

Potential buffering

1. Resilient water and food systems.

2. Capacity to prepare for severe weather.

3. Ability to prevent, treat and recover from disease.

Slide 59 · WHO estimate quoted by Robbins

≈250,000

Additional annual deaths projected for 2030–2050

The textbook attributes this approximate projection to the WHO, reflecting multiple climate-associated disease pathways.

Historical estimate cited by the book, not an observed contemporary mortality count.

Slide 60 · Interpret causal claims with care

Supported by the chapter

1. Climate change alters several environmental exposures.

2. Those exposures contribute to specified classes of disease.

Not established by this excerpt

1. Individual diagnostic criteria or causal attribution.

2. Updated estimates, pathogen-specific incidence or intervention effect sizes.

Population-level burden and patient-level diagnosis are different questions.

Slide 61 · Health protection operates at several stages

Address drivers

Reduce accumulation of climate-warming gases.

Reduce exposure

Improve preparation for heat, flooding and air hazards.

Limit consequences

Protect clean water, food access and displaced populations.

Slide 62 · Paris Agreement: Temperature goals

1.5°C

Effort to limit warming above preindustrial levels

The 2015 international agreement: Well below 2°C, while pursuing efforts toward 1.5°C.

This is an agreed temperature goal, not a forecast of achieved warming.

Slide 63 · Mitigation and adaptation answer different questions

Mitigation

1. Addresses greenhouse-gas sources and sinks.

2. Acts upstream of future climate hazards.

Adaptation

1. Reduces exposure and vulnerability to hazards.

2. Protects infrastructure and health-system capacity.

Both climate magnitude and capacity to mitigate damage as determinants.

Slide 64 · Case 1: Flooding followed by enteric illness

After unusually heavy rainfall, a community experiences flooding, damaged sewage infrastructure and a cluster of diarrheal illnesses.

Which environmental step most directly links the flood to infection?

A. Change in solar radiation

B. Contamination of drinking water

C. Melting of sea ice

Slide 65 · Case 2: Heat and respiratory deterioration

During an extreme-heat episode with degraded air quality, local services report more cardiovascular and respiratory presentations.

What is the most defensible interpretation?

A. Only heat has a health effect

B. Only pollution has a health effect

C. Heat and pollution can operate together

Slide 66 · Case 3: Altered vector range

A region with shifting temperature and seasonal weather conditions reports changes in the presence of disease-carrying vectors.

What changes may follow before a disease case is confirmed?

A. Vector number and geography

B. A fixed global increase in all infections

C. A new diagnostic cutoff

Slide 67 · Synthesis: The four causal chains to retain

Thermal

Heat → illness / vascular burden

Environmental

Flood → contaminated water → infection

Ecologic

Climate → vectors → infection

Systemic

Crop / coast disruption → social harm

Slide 68 · Questions to ask when interpreting a claim

Is the statement an observation, estimate or conditional projection?

What exposure links the climatic change to the clinical outcome?

Is the outcome direct, ecologically mediated or socially mediated?

Does the source provide a disease diagnosis, or only a population-level association?

Slide 69 · Primary source and figure provenance

Robbins, Cotran & Kumar. Pathologic Basis of Disease — Health Effects of Climate Change.

The integrated climate–health outcome figure in the textbook credits CDC Foundation resources.

Historical measurements and projections are presented as reported in the primary textbook; they are not current measurements.