By: Eliana Zhang
It is August 2021 and you live in New York’s concrete city. There are no trees in the neighborhood, and the heat has nowhere to go except for the asphalt you stand on and the building you live in. The city, you think, is more of an oven than anything. As temperatures soar into the hundreds and the air around you boils, a cooling system still has yet to magically appear in your apartment. You, like many other New Yorkers, can only get your dizzy and clammy self in front of a fan as you listen to the latest news report calling for citizens of New York to conserve energy in this heat wave… which is infuriating, because you know for a fact that the Times Square billboards are as brightly lit as ever.
This used to be a once-in-a-lifetime occurrence but imagine that these extreme heat waves happen every other year. Pretty soon, you won’t have to merely imagine.
The Greenhouse Effect (AKA: The Mother of Heat Waves... And Heat in General)
Why do heat waves happen? And why do we even have this much heat anyway? The answer to both of these questions is the greenhouse effect.
The greenhouse effect gets its name from, you guessed it, a greenhouse. You may have seen it around before, but if you haven’t, a greenhouse is typically a building made of glass and plastic panels that works by converting light energy into heat energy. Light rays from the sun enter these transparent panels, where they are then absorbed by plants and other objects and converted into heat. These objects initially release the heat very slowly-- you may have noticed that it doesn’t take very long for things like a dark table to warm up, but it does take a long time for them to cool down. As these objects cool down, they are, in reality, transferring their absorbed heat energy to the air. When the heat is released, however, it remains trapped in the greenhouse because of the panels, whose transparency allows light energy to go through but physically blocks heat energy from doing so. This often results in the greenhouse getting too hot, which is why many have windows, vents, and fans to release hot air when needed.
So why do we call it the “greenhouse effect”? It describes the way Earth acts as its own giant greenhouse. Its “plastic paneling” is the thick layer of atmosphere that keeps warm air from escaping into space. In it, heat-trapping “greenhouse gases” like methane, water vapor, nitrous oxide, ozone, and carbon dioxide filter out much of the sun's harmful radiation while trapping its heat. Without this layer, the Earth’s temperature would be a frigid -18 degrees Celsius, when with the layer, the Earth is usually an average of 15 degrees Celsius (59 degrees Fahrenheit).
Humans contribute towards several of these “greenhouse gases” in tremendous quantities through activities such as transportation and farming. As these gases increase in quantity in the atmosphere, they trap even more heat, which not only increases heat across the planet but also sabotages some of the Earth’s “heat-release” systems like the polar ice caps.
With the increased human activity we’ve been seeing since the Industrial Revolution, hot days have been getting both hotter and more frequent. Heat waves are becoming more common as well. This trend can already be shown through data, as in 2003, 70,000 people in Europe died as a result of the June-August heat wave, and in 2010, 56,000 deaths occurred during a 44-day heatwave in Russia. People may ridicule some of these deaths, comparing the relatively soaring temperatures to the normally sky-high climate of their own region, but it needs to be stated that a person whose physiology is not used to extreme temperatures undoubtedly has different levels of tolerance and that regardless of how ridiculous it may seem to someone who faces more than 36 degrees Celsius daily, lost lives are nothing to laugh about.
2. Heat Waves Themselves and the Disappearing Nighttime Cool-Down
The National Weather Service explains that heat waves form when "high pressure aloft, from 10,000 to 25,000 feet (3,000 to 7,600 meters), strengthens and remains over a region for several days up to several weeks,” bringing severe temperature along with it.
Heat waves are particularly deadly when the temperature rises suddenly. Human bodies are adaptable and can become acclimatized over a longer duration of time, but when there are sudden increases in temperature and humidity, people are the most vulnerable-- most cases of heat stroke occur within the first three days of a heat wave.
Even when expected, heat and humidity sabotage sweat’s attempts to dissipate body heat, bringing fatal consequences along with it at its extreme. As temperatures rise, the air can hold more moisture-- an unfortunate feedback loop, considering how water vapor accounts for around 85% of the greenhouse effect.
Humidity also traps heat at night, which results in unusually high nighttime temperatures. As another contributor towards nighttime temperature records, it can heat cities, buildings, roads and infrastructure to up to 50 to 90 degrees hotter than the air while natural surfaces remain closer to air temperatures. Just as stated previously, objects take a lot longer to cool down than they do to cool up-- but as they cool down, the heat gets released into the surrounding air. The slow release of heat from the infrastructure overnight combined with high humidity rates can therefore keep cities much hotter than surrounding areas… when nights usually provide the opportunity for people to cool down from the day’s heat.
On average, nights are warming faster than days. Simultaneously, these unusually hot summer nights can lead to a significant number of deaths. Human bodies need time to cool off, and that typically happens in sleep, when body temperature naturally dips. After a hot day, it’s imperative that people have an opportunity to bring their core body temperature down. When overnight temperatures are high, however, you lose that relief and put more of heat’s physiological strain on your body.
3. Heat and Health
Extreme heat is one of the leading causes of weather-related deaths in the United States, killing an average of 600+ per year, more than all other events—save for hurricanes—combined. Fittingly, the National Oceanic and Atmospheric Administration lists heat waves as four of the top ten deadliest U.S. disasters since 1980.
Heat stress happens when the body is unable to cool itself effectively and loses its homeostasis. Heat gain occurs in the human body through a combination of external heat from the environment and internal body heat generated from metabolic processes like ATP synthesis. Rapid rises in heat gain can compromise the body’s ability to regulate temperature—such as how humidity sabotages the body’s attempt to sweat the heat out—and can result in a myriad of illnesses, including heat cramps, heat exhaustion, heatstroke, and hyperthermia. They can also worsen chronic illnesses, including cardiovascular, respiratory, cerebrovascular, and diabetes-related conditions.
Heat’s indirect health effects, too, cannot be overstated. Hot days can also bring with them increased ozone levels, which in turn affects NOX (nitrogen oxide pollution) levels. In addition, a greater use of indoor air conditioning systems requires more electricity and thus can emit more of other types of pollution, including particulates.
Heat also has important indirect health effects. It can alter human behavior, the transmission of diseases, health service delivery, air quality, and instrumental infrastructure such as energy, transport, and water systems. The scale and nature of these impacts depend on the timing, intensity and duration of the heatwave, the level of acclimatization, and the adaptability of the local population, infrastructure and institutions to the prevailing climate. The precise threshold at which temperature represents a hazardous condition varies by region, other factors such as humidity and wind, local levels of human acclimatization, and preparedness for heat conditions.
The negative health impacts of heat are predictable and, more importantly, preventable with specific public health actions. The World Health Organization advises that the general public keep an eye out for symptoms of heat exhaustion and take measures to cool themselves down while coping with extreme heat.
The signs of heat exhaustion include:
a headache
dizziness and confusion
loss of appetite and feeling sick
excessive sweating and pale, clammy skin
cramps in the arms, legs and stomach
fast breathing or pulse
a high temperature of 38C or above
being very thirsty
What did you learn?
Why is it called the “greenhouse effect”? It describes the way Earth acts as its own giant greenhouse. Earth’s substitute for a greenhouse’s “plastic paneling” is the thick layer of atmosphere that keeps warm air from escaping into space. In it, heat-trapping “greenhouse gases” like methane, water vapor, nitrous oxide, ozone, and carbon dioxide filter out much of the sun's harmful radiation while trapping its heat. Without this layer, Earth would be a lot colder than it is right now.
Why are high nighttime temperatures so dangerous? Human bodies need time to cool off, and that typically happens in sleep, when body temperature naturally dips. After a hot day, people need to have an opportunity to bring their core body temperature down. When overnight temperatures are high, however, they lose that relief and put more of heat’s physiological strain on their body.
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