Public Health6 min readUpdated February 2, 2026

Health and the climate crisis

Introduction

The intersection of Health and the Climate Crisis is an increasingly vital component of the MCCQE1 and the Public Health curriculum. For Canadian medical graduates, understanding the specific environmental challenges facing Canada—from wildfires in the West to vector-borne disease expansion in the East and rapid warming in the North—is essential.

This topic integrates closely with the CanMEDS Health Advocate role. Physicians are expected to recognize environmental determinants of health and advocate for sustainable healthcare practices.

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CanMEDS Focus: As a Health Advocate, you must identify the health needs of individual patients and communities related to climate change and promote environmental sustainability within the healthcare system (Planetary Health).

The Spectrum of Climate Health Impacts

Climate change acts as a “threat multiplier,” exacerbating existing health issues and introducing new ones. The impacts are generally categorized into direct, indirect, and health system impacts.

1. Direct Physical Health Impacts

Extreme Heat Events

Canada is experiencing more frequent and intense heatwaves (e.g., the 2021 Western North America heat dome).

Heat Exhaustion

Pathophysiology: Volume depletion and heat stress. <br/>Symptoms: Heavy sweating, pallor, muscle cramps, fatigue, dizziness, headache, nausea.<br/>Vitals: Temperature normal or slightly elevated (<40°C), tachycardia, hypotension.<br/>Management: Move to cool place, oral rehydration, active cooling.

Extreme Weather Events

Wildfires: Increased incidence in British Columbia, Alberta, and the Boreal forest.
- Health Risk: PM2.5 inhalation leading to exacerbations of Asthma and COPD.
- Acute Effects: Eye irritation, bronchitis, reduced lung function.
Floods: Increased risk in Manitoba and coastal regions.
- Health Risk: Waterborne diseases, mold exposure, injury, displacement.

2. Ecological and Indirect Impacts

Vector-Borne Diseases

Changing climates allow vectors to survive in previously inhospitable Canadian latitudes.

Disease	Vector	Canadian Trend	MCCQE1 Clinical Pearl
Lyme Disease	Ixodes scapularis (Blacklegged tick)	Expanding North/East (ON, QC, NS, MB)	Erythema migrans (bullseye rash). Tx: Doxycycline.
West Nile Virus	Culex mosquitoes	Endemic in parts of Canada	Flu-like sxs, rare neuroinvasive disease. Supportive care.
Blastomycosis	Soil fungus	Endemic in NW Ontario/Manitoba	Pulmonary infection mimicking pneumonia/TB.

Air Quality

Ground-level ozone and particulate matter (PM) increase with higher temperatures and stagnant air masses.

Cardiovascular: Increased risk of MI, stroke, and arrhythmias.
Respiratory: Increased ED visits for respiratory distress.

3. Mental Health Impacts

Psychological Terms to Know

Eco-anxiety: Chronic fear of environmental doom.
Solastalgia: Distress caused by environmental change impacting people while they are directly connected to their home environment.
PTSD: High prevalence following evacuation from wildfires or floods.

Vulnerable Populations in Canada

Climate change does not affect all Canadians equally. Understanding these disparities is crucial for the PHELO component of the MCCQE1.

Indigenous Communities

Northern Canada: Warming at 2x to 3x the global rate.
Impacts: Melting permafrost affects housing stability; changing ice patterns affect traditional hunting/gathering (food insecurity); loss of cultural practices.

The Elderly and Socially Isolated

Highest mortality during heatwaves (e.g., Montreal 2018, BC 2021).
Risk factors: Lack of air conditioning, limited mobility, polypharmacy (anticholinergics/diuretics affecting thermoregulation).

Low Socioeconomic Status (SES)

Often live in “Urban Heat Islands” with less green space.
Less capacity to adapt (e.g., afford AC or air filtration).

Canadian Guidelines and Monitoring Tools

Familiarity with these tools is expected for Canadian medical practice.

Air Quality Health Index (AQHI)

Unlike the old AQI, the Canadian AQHI measures the health risk associated with air pollution on a scale of 1-10+.

1-3 (Low Risk): Enjoy outdoor activities.
4-6 (Moderate Risk): Consider reducing or rescheduling strenuous activities outdoors if you are experiencing symptoms.
7-10 (High Risk): At-risk populations should reduce or reschedule strenuous outdoor activities.
10+ (Very High Risk): Everyone should avoid strenuous outdoor activities.

Heat Alert and Response Systems (HARS)

Health Canada and provincial bodies issue alerts based on region-specific thresholds.

Clinical Management and Mitigation

The “Green” Physician

The Canadian healthcare system contributes approximately 4.6% of the country’s total greenhouse gas emissions.

Step 1: Mitigation (Reducing the Footprint)

Prescribing: Switch from Metered Dose Inhalers (MDIs - contain hydrofluorocarbons) to Dry Powder Inhalers (DPIs) where clinically appropriate.
Choosing Wisely: Reducing unnecessary testing reduces waste and carbon emissions.
Virtual Care: Reduces patient travel emissions.

Step 2: Adaptation (Preparing Patients)

Identify vulnerable patients (respiratory/cardiac disease, elderly).
Review Action Plans (e.g., Asthma Action Plan) specifically for wildfire smoke events.
Review medications that impair heat dissipation (e.g., antipsychotics, beta-blockers).

Step 3: Advocacy

Advocate for active transport (walking/cycling) which has co-benefits of reducing emissions and improving cardiovascular health.

Abbreviations Checklist


AQHI  : Air Quality Health Index
GHG   : Greenhouse Gas
HARS  : Heat Alert and Response Systems
MDI   : Metered Dose Inhaler
DPI   : Dry Powder Inhaler
PM2.5 : Particulate Matter &lt;2.5 micrometers
VOC   : Volatile Organic Compounds

Key Points to Remember for MCCQE1

Heat Stroke vs. Heat Exhaustion: The defining feature of heat stroke is CNS dysfunction (confusion, ataxia) and core temp usually >40°C.
Lyme Disease: Know the geography (expanding) and the rash (Erythema Migrans). It is a clinical diagnosis in the early stage; do not wait for serology to treat.
Vulnerability: Indigenous populations in the North face the most rapid climate changes affecting food security and infrastructure.
Co-benefits: Interventions that help the climate often help the patient (e.g., active transport reduces obesity and emissions; plant-rich diets reduce cardiac risk and land use).
AQHI: Know the advice for “At-Risk” populations (elderly, children, those with pre-existing conditions) during High Risk (7-10) periods.

Sample Question

Clinical Scenario A 78-year-old man is brought to the Emergency Department by his daughter during a prolonged heatwave in July. The daughter reports that she went to check on him because he wasn’t answering the phone. She found him confused and lethargic in his apartment, which does not have air conditioning. He has a history of hypertension and schizophrenia. His medications include hydrochlorothiazide and olanzapine.

On examination, he is stuporous and responds only to painful stimuli. His skin is hot and dry. Vital signs are:

BP: 95/60 mmHg
HR: 120 bpm
RR: 24/min
Rectal Temperature: 40.8°C (105.4°F)
O2 Sat: 96% on room air

Which of the following is the most appropriate immediate management step?

Options

Choose an answer, then check it against the explanation.

References

Health Canada. (2023). Health Facilities and Services: Climate Change and Health. Government of Canada.
Canadian Association of Physicians for the Environment (CAPE). (2022). Climate Change Toolkit for Health Professionals.
Public Health Agency of Canada. (2023). Lyme disease: For health professionals.
Cheng, J. J., & Berry, P. (2013). Health co-benefits and risks of public health adaptation strategies to climate change: a review of current literature. International Journal of Public Health.
Royal College of Physicians and Surgeons of Canada. CanMEDS 2015 Physician Competency Framework.