Cool Ideas and Hot Topics: Measuring Temperature and Why it Matters
What do temperature measurements tell you?
Take out your phone, slide your fingers across the screen, and within seconds you can reach the temperature. This figure has reached unprecedented highs in the United States and across the globe with increasing frequency. While temperature may seem like a straightforward measurement, subtle variations in how it is quantified represent important differences in how our bodies experience heat.
Typically, the number displayed on the weather application on a phone is the “dry bulb” temperature; the temperature without consideration of the moisture in the air. However, this measure fails to account for a critical defense our bodies use to prevent us from overheating: sweat. The evaporation of sweat from our bodies is less effective in humid temperatures. With more water in the air on humid days, sweat evaporates more slowly, hindering its ability to cool you down. Thus, on hot days that require more cooling (that is, more sweating) with high levels of humidity (less effective sweating), our bodies are especially susceptible to heat stress. In addition to causing medical conditions such as heat exhaustion or heat stroke in certain conditions, heat stress may also exacerbate health conditions such as heart failure, chronic kidney disease, and mental health disorders. Therefore, with measures that incorporate humidity, we can more accurately determine the heat stress people experience.
For example, the heat index uses temperature and relative humidity in the shade to estimate heat stress. In contrast, the wet bulb globe temperature estimates heat stress in the sun using the variables of the heat index in addition to wind speed, cloud cover, and sun angle.
Comparing Web Bulb Global Temperature and Heat Index
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Measured in the sun: yes
Measured in the shade: no
Uses temperature: yes
Uses relative humidity: yes
Uses wind: yes
Uses cloud cover: yes
Uses sun angle: yes
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Measured in the sun: no
Measured in the shade: yes
Uses temperature: yes
Uses relative humidity: yes
Uses wind: no
Uses cloud cover: no
Uses sun angle: no
Source: weather.gov
By accounting for these critical factors, we may better understand the impact high temperatures have on our health.
Still, even if the temperature on your phone defaulted to these more complete measures of heat, it may not accurately represent the heat stress everyone in your town experiences. With the urban heat island effect, areas with more roads and buildings absorb more heat, leading to higher temperatures in more densely population areas.
Additionally, historically racist policies like redlining –the labeling of Black communities as hazardous investments– has perpetuated localized chronic disinvestment and fewer heat-preventative measures, such as parks and trees, in these marginalized neighborhoods. These environmental factors are further compounded by individual vulnerability to heat stress due to factors such as socioeconomic status, which indicates the resources one may have to mitigate their exposure to extreme temperatures.
While the world braces for the possibility of heatwaves with temperature and humidity values too extreme for the human body to endure, we must also acknowledge the very present threat that heat and humidity pose for the most vulnerable individuals in our communities. Understanding why the heat index and the wet bulb globe temperature are crucial tools in characterizing and preventing the effects of heat stress on individuals and communities.
