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Wet-Bulb Temperature: The Climate Crisis Effect We Can’t Ignore

Why is it in the news ?

As large parts of India experience severe heat waves, the need to protect against extreme temperatures is now more important than ever. As per the recent news, 13 people in Maharashtra died from sunstroke. However, these reports usually focus only on high temperatures and overlook important factors like humidity, which greatly affects how heat impacts our bodies.

The Role of Humidity in Heat Stress

  • Elevated temperatures pose risks independently, but when humidity is also considered, the danger increases significantly.
  • This is measured by the wet-bulb temperature (WBT), which shows when our bodies can not cool down effectively by sweating.
  • The WBT is measured by covering a thermometer bulb with a wet cloth. As the water evaporates, it cools the thermometer, indicating the point where the air can’t absorb more moisture from sweat.
  • Simply, Wet-bulb temperature (WBT) is the lowest temperature air can reach by evaporating water at constant pressure.

Why Wet-Bulb Temperature is Important ?

  • The significance of the wet-bulb temperature lies in its indication of potentially hazardous conditions. When humidity goes up, the wet-bulb temperature also rises, making it harder for the body to cool down.
  • As the surrounding temperature nears the skin’s temperature of about 35°C, the body’s typical cooling mechanisms become less effective. This happens because the air holds more moisture, slowing down sweat evaporation, and making it harder for the body to cool down.

Limits of Human Endurance

  • According to a study in ScienceDirect, even those accustomed to hot weather find it tough to do outdoor activities when the wet-bulb temperature hits 32°C. This is like a heat index of 55 degrees, which takes into consideration in both air temperature and humidity.
  • When the wet-bulb temperature hits 35°C, even healthy people can’t survive, regardless of access to water, shade, or rest. This can occur at an air temperature of 45°C with 50% humidity or 39°C with 75% humidity, according to the National Institutes of Health (NIH). Simplify
  • In extremely high wet-bulb temperatures, sweating no longer helps the body cool down. Being in these conditions for a long time can cause organ failure and death within hours, even for healthy people. This highlights the urgent need for cooling methods and quick medical help during heatwaves.

The Current Scenario: Rising Temperatures and Humidity

  • Recently, a weather station in Delhi recorded a scorching maximum temperature of 52.9°C, making it the highest ever in India.
  • While initially thought to be a mistake in measurement, this extreme temperature reflects the severe heat conditions this year. Many people believe this summer is the hottest they’ve ever felt, which is backed by data from the India Meteorological Department.
  • The Centre for Science and Environment (CSE) observed a concerning trend of higher average humidity levels in Delhi during summer, increasing from 52.5% in the early 2000s to over 60% in recent years.
  • This rise in humidity makes it tougher for people to cool down, worsening heat stress and raising the chances of heat-related illnesses.


The Deadly Combination of Heat and Humidity

  • The combination of high heat and humidity presents a particularly dangerous situation. Perspiration is our body’s primary cooling mechanism, but its effectiveness diminishes as humidity increases.
  • High moisture content in the air means sweat evaporates more slowly, weakening the cooling effect and potentially leading to heat stress or heatstroke.
  • Global studies on human tolerance indicate that spending five hours or more outdoors involves wet-bulb temperatures above 35°C can be fatal.
  • This alarming statistic highlights the severe risks faced by millions of workers, especially those without access to air-conditioned environments.

Laboratory Insights: The Penn State HEAT Project

  • Researchers at Penn State University tested the heat tolerance of healthy young men and women by gradually increasing temperature and humidity in a controlled environment.
  • They monitored their core body temperatures and identified the point when the temperature began to rise steadily, calling it the critical environmental limit.
  • As per the findings, while earlier studies considered 35°C safe, current research discovered that even around 31°C, core body temperature begins to rise dangerously.
  • This limit equals 31°C at 100% humidity or 38°C at 60% humidity, showing how small the safe margin is.

Implications for Vulnerable Populations

  • The initial studies focused on young, healthy people, but the situation is even more serious for vulnerable groups like the elderly and those with existing health issues.
  • Getting older makes it harder to tolerate heat, and chronic illnesses or certain medications can make people even more sensitive to heat stress.
  • Research shows that 80% to 90% of heatwave-related deaths are among people over 65, highlighting the urgent need for specific interventions.

Mitigation Strategies: Staying Safe in Extreme Heat

  • To stay safe in extreme heat, it’s crucial to drink enough water and find cool places, even if just for a little while.
  • Making cooling centers more available and helping vulnerable people stay cool are important. But it’s challenging because energy costs are high, and power cuts happen often during heatwaves.
  • It’s important for people who work outside or spend time outdoors to know about wet-bulb temperature and take steps to stay safe like wearing light clothes, taking breaks in shaded or cool spots, and drinking enough water regularly.

The Broader Picture: Climate Change and Future Risks

  • Heatwaves are becoming more common and severe because of climate change. As the world gets hotter and more humid, more places are reaching dangerously high wet-bulb temperatures.
  • This trend is expected to continue, with climate experts forecasting more frequent and intense heat waves in the future.
  • India’s situation reflects a global problem. With its large population and limited access to air conditioning and cooling systems, the country is especially at risk from extreme heat.

Addressing this issue requires a multi-faceted approach, including:

  1. Public Awareness and Education: We need to inform people about the risks of high wet-bulb temperatures and create awareness about hydration, heat sickness and emergency medical aid.

2.Infrastructure Development: It’s crucial to invest in infrastructure that helps communities deal with heat waves better like more cooling centers, city cooling action plan, sustainable energy for air conditioning.

  1. Policy and Regulation: Governments must make rules to keep vulnerable people safe during heatwaves. This includes making sure outdoor workers have safe conditions and helping people afford cooling options.
  2. Climate Mitigation and Adaptation: It’s important to tackle the main reasons for climate change by cutting down on greenhouse gases.

Conclusion: Facing the Heatwave Challenge

Rising wet-bulb temperatures and their health impacts demand immediate action. Recent heat waves in India emphasize the danger of hot and humid conditions. With temperatures increasing worldwide, it’s critical to recognize and address the risks associated with high wet-bulb temperatures.

Protecting against extreme heat requires collective action,raising awareness, infrastructure improvements, and policy changes. Taking proactive measures can mitigate risks and safeguard vulnerable populations from the worsening effects of climate change.

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