Climate Change and Heat Impacts

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Headshot of Anne Grossman, MD, FACP · Assistant Professor, Medical Education and Clinical Sciences
Anne Grossman
MD, FACP · Assistant Professor, Medical Education and Clinical Sciences
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Table of Contents

Mini Lesson: Extreme Heat

In this mini lesson, you'll find:

  1. Case studies.
  2. Definitions.
  3. Review questions.


Go to the Mini Lesson: Extreme Heat.

Local Government Response to the 2021 Pacific Northwest Heat Dome

Play Video about planetary-health-heat-impact-image2

(approximately 25 minutes—you can stop watching at 58 min.)

Direct and indirect health impacts of extreme heat

Source: Scale and nature of the health impacts of heat. World Health Organization.
Source: Main Heat Vulnerability Factors. World Health Organization.
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Heat-related Morbidity and Mortality

These materials are based on the PowerPoint presentation by Jeremy Hess, MD, MPH Professor, Schools of Medicine and Public Health Director, Center for Health and the Global Environment (CHanGE).

Rationale

Heat Is Central to Climate Change

Fundamentally, climate change is driven by increased retention and re-radiation of heat by the Earth’s atmosphere.

planetary-health-heat-impact-euthermic-graph

Normal human body-temperature (euthermia) is the typical body temperature range stated as 36.5°C–37.5°C (97.7°F–99.5°F).

planetary-health-heat-impact-mortality-temperature-chart

The minimum mortality temperature (MMT) is an indicator to characterize associations between temperature and health, regarding long-term adaptation to climate.

planetary-health-heat-impact-shifting-temperature-distribution-graph

This chart shows the variation and distribution of land temperature anomalies over time. As the planet warms, the peak of the distribution shifts right. The distribution of temperatures broadens, which may be due to differential regional warming rather than increased temperature variability at any given location.

These distributions are calculated from the Goddard Institute of Space Studies GISTEMP surface temperature analysis. 

planetary-health-heat-impact-implications

  • An extreme heat event with a 10-year return period in the historic climate now occurs 2.8 times as often.
  • An extreme heat event with a 50-year return period now occurs 4.8 times as often.

Health Effects of Extreme Heat

Heat Transfer and Heat Balance

Narrow Temperature Range

  • Behavioral maintenance.
  • Physiological maintenance.


Exogenous Heat

  • Solar radiation.
  • Environment.

Endogenous Heat

  • Baseline metabolic activity.
  • Additional physical activity.


Heat Dissipation

  • Radiation.
  • Conduction.
  • Convection.
  • Evaporation.

Thermoregulation

Heat Impacts the Body

System Physiology Mechanisms Compensation Decompensation Outcomes
Cardiac
Increased cardiac output to meet increased metabolic demand
Increased inotropy and chronotropy via baroreceptors and other pathways
Maintained or increased cardiac output via increased heart rate and contractility
Decreased cardiac output due to decreased stroke volume
Peripheral, central hypoperfusion; acute coronary syndrome; myocardial infarction
Vascular
Peripheral vasodilation, central vasoconstriction
Sympathetic nervous system and local reflex pathways
Enhanced peripheral blood flow to facilitate cooling and sweating
Decreased splanchnic blood, tissue hypoxia, endotoxemia, bloodstream infection
Sepsis and septic shock
Renal
Increased reabsorption to compensate for insensible water and electrolyte losses
Vasopressin, Renin-angiotensin-aldosterone system, renal sympathetic nerve activity
Increased free water retention, increased electrolyte retention, decreased renal blood flow
Insufficient renal perfusion, inability to maintain adequate water and electrolyte reabsorption rates
Dehydration, electrolyte abnormalities, acute kidney injury
Immune
Activation of coordinated stress response
Endothelial, epithelial, leukocyte response via cytokines, heat shock proteins
Protection against tissue injury, enhanced repair
Increased hypoxemia, cytotoxic injury lead to dysregulated immune response
Distributed shock similar to systemic inflammatory response syndrome
Hemato-logic
Initial increase, then decrease, in plasma volume
Sympathetic nervous system, activation of coagulation and fibrinolytic pathways
Support cardiac output, insensible water losses
Increased viscosity, altered coagulation
Disseminated intravascular coagulation, tissue hypoxemia and cell death
Central Nervous System
Behavioral and physiologic responses to reduce exogenous heat exposure, increase heat loss
Multiple thermoregulatory pathways coordinated by the preoptic hypothalamus
Behavioral, physiologic responses that reduce heat load and increase heat loss
Cerebral hypoperfusion and dysregulation of thermal homeostasis
Confusion, delirium, dizziness, weakness, agitation, combativeness
Reproductive
Reduced placental blood flow to support peripheral vasodilation
Sympathetic nervous system and local reflex pathways
Reduced placental blood flow with relative preservation of nutrient transfer to fetus
Dysregulation of thermal homeostasis leading to core temperature over teratogenic threshold
Miscarriage, pre-term labor

Heat Illness

Your body cools itself by sweating. During hot weather, especially with humidity, your body temperature can rise to dangerous levels, and you can develop a heat illness.

Heat-related illnesses include: heat stroke, heat exhaustion, and heat cramps.

Learn more about Heat Illness.

planetary-health-heat-impact-edema-image

Mild edema on dependent areas, often seen during early heat acclimitization, resolves spontaneously in a few days.

Edema from training in heat after time off. A compression sock was worn on the right foot and regular running socks on the left foot.

Our skin protects us from infections, chemical exposures, and harmful ultraviolet light. Heat rash (prickly heat or miliaria) is a mild inflammation of clogged sweat ducts. Heat rash can be diffuse, pruritic, maculopapular, or vesicular in the setting of heat exposure, often with insulating clothing or swaddling.

Learn more about Heat Rash.

planetary-health-heat-impact-miliaria-crystalline-image Miliaria Crystalline

Miliaria Rubra

Miliaria Pustulosa

Miliaria Profunda

Rare, self-limiting condition in patients with short, intense heat exposure, with hyperventilation, paraesthesias.

Painful contractions of frequently used muscle groups.

Brief loss of consciousness in the setting of heat exposure without evidence of seizure activity, stroke, or overdose.

Syndrome with generalized weakness, exhaustion, lightheadedness, nausea, limiting function, without recent infection may or may not be exertional.

Altered mental status (including disorientation, delirium, seizure, obtundation), with elevated core body temperature.

Prevention, Diagnosis, and Treatment

planetary-health-heat-impact-primary-prevention-illustration

Prevention

Primary Prevention
  • Acclimatize: Risks are greatest at the beginning of heat season.
  • Prevent exposure on hot days, heed heat warnings.
  • Prevent over-exertion.
  • Prevent exposure to heat sources.
  • Discuss heat-relief plans with employers, supervisors, and employees.
Secondary Prevention
  • Know early symptoms of heat illness.
  • Take time to cool down.
  • Monitor hydration, (e.g., look for dark urine).
  • Provide for cooler, shaded places to rest and drink water.
  • Be ready to call for help.
Tertiary Prevention
  • Call for prompt medical attention, (e.g., 911).
  • Assess ABCs.
  • Rapid cooling: Expose, wet, evaporate.
  • Targeted passive cooling: Ice packs in groin, axilla.
  • Rule out alternative causes.

Diagnosis

  • Primarily clinical.
  • History is often important, include:
    • History of time, location, exogenous heat sources, activities, and cooling measure.
    • For more severe forms, pertinent negatives (infection, overdose, known seizure history) are also important to rapidly ascertain.
  • Laboratory and imaging tests are often used to support clinical diagnosis and guide therapy.

Treatment

  • Acute syndrome often primarily related to heat dissipation more than dehydration.
  • More chronic presentations typically related to dehydration more than elevated temperature.

Couchama and Knochel 2002

Put It All Together

2006 California Heat Wave

BACKGROUND: Climate models project that heat waves will increase in frequency and severity. Despite many studies of mortality from heat waves, few studies have examined morbidity.

OBJECTIVES: In this study, we investigated whether age or race/ethnicity groups experienced increased hospitalizations and emergency department (ED) visits overall or for selected illnesses during the 2006 California heat wave.

METHODS: We aggregated county-level hospitalizations and ED visits for all causes and for 10 cause groups into six geographic regions of California. We calculated excess morbidity and rate ratios (RRs) during the heat wave (15 July to 1 August 2006) and compared this data with those of a reference period (8–14 July and 12–22 August 2006).

RESULTS: During the heat wave, 16,166 excess ED visits and 1,182 excess hospitalizations occurred statewide. ED visits for heat-related causes increased across the state [RR=6.30; 95% confidence intervals (CI), 5.67–7.01], especially in the Central Coast region, which includes San Francisco. Children (0–4 years of age) and the elderly (>65 years of age) were at risk. ED visits also showed significant increase for acute renal failure, cardiovascular diseases, diabetes, electrolyte imbalance, and nephritis. We observed significantly elevated RRs for hospitalizations for heat-related illnesses (RR=10.15; 95% CI, 7.79–13.43), acute renal failure, electrolyte imbalance, and nephritis.

CONCLUSIONS: The 2006 California heat wave had a substantial effect on morbidity, including regions with relatively modest temperatures. This suggests that population acclimatization and adaptive capacity influenced risk. By better understanding these impacts and population vulnerabilities, local communities can improve heat wave preparedness to cope with a globally warming future.

Chronic Disease Exacerbations

Our Experience

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  • Historically unprecedented extreme heat events.
  • Relatively short advance warning.
  • Acute-on-chronic capacity constraints.
  • Large vulnerable populations, insufficient protections.

planetary-health-heat-impact-healthcare-workforce-graphic planetary-health-heat-impact-registered-nurses-graphic

  • Historically cool regional climate:
    • Housing built for heat retention.
    • Relatively low AC prevalence.
  • Little lived experience with heat:
    • Relatively low population and health sector awareness.
  • Population growing faster than health care capacity:
    • Differentially constrained by SES.
    • Acute staffing from COVID.

planetary-health-heat-impact-health-impact-graph1 planetary-health-heat-impact-health-impact2-graph

  • The 2021 heat wave is the deadliest weather-related event in Washington history.
  • At least 3,500 ED visits in four-state region (CDC); 100-fold increase in heat-related ED visits on 6/28.
  • We are well prepared for future clinical impacts.
  • We are less prepared for:
    • Presentations outside our expectations.
    • Events beyond our experience.
    • Combinations that overwhelm developed systems.
  • We need information systems that:
    • Give us insight into changing risk distributions.
    • Strategies for reducing emerging risks as they occur.
    • Methods for implementing quickly and at scale.
  • Assuming current trends persist, we will very likely need to prepare for a new risk regime circa 2050.

Intervention

Build Resilience

Ahmedabad Heat Action Plan

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Relative risk of death pre- and post-HAP
planetary-health-heat-impact-scaling-up-effective-intervention
Scaling up effective interventions

S U M M A R Y

  • Humans are euthermic and maintain heat balance.
  • Excess heat threatens normal function.
  • Climate change is warming environments rapidly.
  • Body systems attempt to compensate; this can stress body systems.
  • Decompensation leads to heat stroke.
  • Diagnosis is clinical; rapid cooling is essential.
  • Health systems and larger communities are at risk.
  • Broad efforts, (e.g., HAPs, can reduce risks).
Planetary Health Resources

Image credits

Unless otherwise noted, images are from Adobe Stock.