Measuring extreme temperatures: A guide on determining hazardous heat levels

Measuring extreme temperatures: A guide on determining hazardous heat levels

In the rapidly changing climate, understanding and combating heat stress has become a pressing concern for health authorities worldwide. One tool used to assess heat stress levels is the Universal Thermal Climate Index (UTCI), employed by Copernicus, the EU's climate monitor. UTCI ranks heat stress levels from moderate to extreme, taking into account temperature, humidity, wind, sunshine, and radiated heat.

However, it's important to note that these indices are not without limitations, and their effectiveness can vary depending on the climate and location. For instance, the UTCI may not be effective in global south countries, according to heatwave expert John Nairn.

Heat, often referred to as a "silent killer" by Alejandro Saez Reale of the World Meteorological Organization (WMO), can be particularly dangerous because symptoms are not easily evident. As climate change makes heatwaves longer, stronger, and more frequent, people across the planet will be increasingly exposed to conditions that test human endurance. Infants, the elderly, people with health problems, outdoor workers, and city dwellers surrounded by concrete and brick are particularly vulnerable to heat stress.

Several methods are used to measure heat stress. The Wet-Bulb Globe Temperature (WBGT) is the most comprehensive and widely accepted metric. It integrates air temperature, humidity, wind speed, and solar radiation to better mimic the human body's response to heat. In developed regions, like US schools and sports settings, WBGT is favored due to its accuracy, though its use can be limited by instrument availability.

Simpler indices like the Heat Index, used by the US National Weather Service, offer an "apparent temperature" based on heat and humidity in the shade. However, they do not account for wind or solar radiation, making them less accurate than WBGT in many contexts.

Handheld and onsite devices, such as sling psychrometers and modern handheld devices, measure temperature and humidity. While these devices can provide real-time heat stress data, they often capture conditions only at a single location and height, limiting representativeness.

Heat Stress Questionnaires and Educational Tools are also used to assess heat stress risk and provide targeted prevention education, particularly useful in occupational settings where direct environmental measurement may be limited.

Technological advances and education programs help improve heat stress prevention across diverse settings. For example, advances in estimation techniques allow WBGT to be approximated from common weather variables, improving accessibility.

It's crucial to remember that heat stress is a condition caused by the body's natural cooling systems being overwhelmed, leading to symptoms ranging from dizziness to organ failure and death. Sweat cannot evaporate off the skin above a certain heat and humidity limit, causing the body to overheat and expire.

Heat stress is brought on by prolonged exposure to heat and environmental factors that disrupt the body's internal thermostat and temperature regulation. Other thermal stress indices, such as the Tropical Summer Index, Predicted Heat Strain, and mean radiant temperature, are also used to build a more complete picture of heat stress.

However, these indices do not consider the impact of heat beyond health, such as the potential for heatwaves to strain infrastructure like trains or air-conditioners. For instance, Canada has developed the Humidex rating, which combines heat and humidity into one number to reflect the "perceived temperature" and presents the associated risk in a four-step "guide to summer comfort" chart.

As we navigate the challenges posed by climate change, accurate and comprehensive heat stress metrics will be essential to protect public health and safety. The WBGT, despite its limitations, remains the most effective metric worldwide to measure heat stress because it accounts for multiple environmental factors affecting human heat load. However, its use depends on available instrumentation or estimation methods. Simpler indices like heat index or questionnaires are less precise but may be more practical in certain global contexts, especially for occupational health interventions.

Sources: 1. Climate Central 2. International Labour Organization 3. World Meteorological Organization

1. In addressing climate change, heat stress levels have emerged as a critical concern for global health authorities, given its potential to impact mental health, nutrition, and overall health-and-wellness.
2. The Universal Thermal Climate Index (UTCI) is among the tools employed to assess heat stress, considering factors such as temperature, humidity, wind, sunshine, and radiated heat, but its effectiveness can vary depending on climate and location.
3. Aside from UTCI, the Wet-Bulb Globe Temperature (WBGT) is a comprehensive and widely accepted heat stress metric, incorporating air temperature, humidity, wind speed, and solar radiation to better reflect human response to heat.
4. To prevent heat stress, technological advances and education programs are vital. For example, WBGT can be approximated from common weather variables, improving accessibility, and heat stress questionnaires can offer targeted prevention education in occupational settings.
5. Heat stress impacts not only physical health but also environmental science, as prolonged exposure to heat can strain infrastructure like trains or air-conditioners, as observed in the Humidex rating system developed in Canada.

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