4.1 Extreme temperatures: heat waves and cold waves

Extreme temperatures, both hot and cold, pose significant risks to health, infrastructure, and the environment. Heat waves and cold waves can lead to illness, strain power grids, and disrupt ecosystems. Understanding these hazards is crucial for developing effective mitigation strategies.

Climate change is intensifying extreme temperature events, making them more frequent and severe. This shift demands adaptive measures like early warning systems, infrastructure improvements, and sustainable urban planning to build resilience against the growing threat of heat and cold waves.

Impacts of Heat and Cold Waves

Health and Safety Risks

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• Heat waves can lead to heat-related illnesses such as heat exhaustion and heat stroke
• Cold waves can cause hypothermia, frostbite, and other cold-related injuries
• Extreme temperatures disproportionately affect vulnerable populations (elderly, children, low-income communities)
• Exposure to extreme temperatures can exacerbate pre-existing health conditions (cardiovascular disease, respiratory illnesses)

Infrastructure and Energy Impacts

• Extreme temperatures strain power grids causing blackouts or brownouts as demand for heating or cooling surges
• Heat waves can damage roads, bridges, and railways through buckling or melting
• Cold waves can cause freezing and cracking of infrastructure
• Increased energy consumption during extreme temperature events contributes to greenhouse gas emissions and energy costs

Environmental and Agricultural Consequences

• Heat waves can cause crop failures and wildfires, devastating agricultural yields and natural ecosystems
• Cold waves can lead to frost damage and wildlife mortality, disrupting biodiversity and food chains
• Extreme temperatures alter phenology, affecting plant and animal life cycles (migration patterns, flowering times)
• Prolonged exposure to extreme temperatures can lead to long-term changes in ecosystem composition and function

Factors Contributing to Extreme Temperatures

Atmospheric Circulation Patterns

• High-pressure systems trap warm air and prevent cloud formation and precipitation, leading to heat waves
• Displacement of cold Arctic air masses towards lower latitudes, often due to jet stream changes, causes cold waves
• Blocking patterns in atmospheric circulation can prolong the duration of extreme temperature events
• Teleconnections (El Niño, North Atlantic Oscillation) influence the occurrence and severity of extreme temperatures

Urban Heat Island Effect

• Urban areas absorb and re-emit more heat than rural areas due to the prevalence of heat-absorbing surfaces (asphalt, concrete)
• Reduced vegetation in cities limits evaporative cooling and shading, exacerbating heat wave impacts
• Urban geometry, such as tall buildings and narrow streets, can trap heat and limit air circulation
• Anthropogenic heat sources (vehicles, air conditioners, industrial processes) contribute to higher urban temperatures

Antecedent Conditions and Feedback Loops

• Drought conditions preceding a heat wave can amplify its impacts by reducing soil moisture and evaporative cooling
• Wet periods before a cold wave can increase the risk of ice storms and snow accumulation
• Positive feedback loops, such as the snow-albedo feedback, can intensify and prolong extreme temperature events
• Land cover changes (deforestation, urbanization) can alter local and regional climate, influencing extreme temperatures

Mitigating Extreme Temperature Risks

Early Warning Systems and Public Health Measures

• Weather forecasting combined with risk assessment and communication helps communities prepare for extreme temperatures
• Opening cooling or warming centers provides refuge for vulnerable populations during extreme temperature events
• Distributing fans, air conditioners, or blankets to those in need can prevent heat- or cold-related illnesses
• Public education campaigns on staying safe during extreme temperatures (hydration, clothing, checking on neighbors)

Infrastructure Adaptations and Resilience

• Installing reflective or green roofs reduces building heat absorption and improves energy efficiency
• Increasing insulation and upgrading heating and cooling systems helps buildings withstand extreme temperatures
• Urban greening (planting trees, creating parks) mitigates the urban heat island effect and provides cooling benefits
• Improving power grid resilience and developing backup power sources prevents blackouts during extreme temperature events

Sustainable Urban Planning and Design

• Incorporating passive cooling techniques (natural ventilation, shading) in building design reduces energy demand
• Designing cities with a mix of land uses and compact development patterns reduces urban heat island effect
• Preserving and expanding green spaces (urban forests, wetlands) provides ecosystem services and temperature regulation
• Implementing cool pavement technologies (reflective coatings, permeable materials) reduces surface temperatures

Climate Change and Extreme Temperatures

Increasing Frequency, Intensity, and Duration

• Rising global temperatures make it more likely for hot extremes to occur, increasing heat wave frequency and intensity
• Warming of the Arctic due to climate change can disrupt the jet stream, leading to more frequent and severe cold waves
• Climate change extends the length of the warm season, prolonging the period favorable for heat waves
• Nighttime temperatures are rising faster than daytime temperatures, limiting nighttime relief during heat waves

Compounding Risks and Cascading Impacts

• Climate change exacerbates other hazards (drought, wildfires, air pollution) that compound extreme temperature risks
• Extreme temperatures can lead to cascading impacts across sectors (agriculture, energy, transportation, public health)
• Heat waves and cold waves disproportionately affect low-income and marginalized communities, exacerbating social inequalities
• Ecosystem shifts and biodiversity loss due to extreme temperatures can have far-reaching consequences (crop pollination, carbon sequestration)

Projections and Adaptation Imperatives

• Climate models project an increase in the occurrence of record-breaking heat waves and the severity of their impacts
• The intensity and frequency of cold waves may decrease in some regions, but they will still pose significant risks
• Adapting to a changing climate requires a combination of mitigation (reducing greenhouse gas emissions) and adaptation strategies
• Building resilience to extreme temperatures involves improving infrastructure, strengthening social safety nets, and fostering community preparedness
• Integrating climate change projections into risk assessment and planning processes is crucial for long-term resilience