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Wet-Bulb Temperature refers to the temperature of air that contains moisture. As global warming continues, wet-bulb temperatures beyond the limits of human survival are being recorded around the world, making this a crisis we need to respond to urgently.  

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Q. What Is Wet-Bulb Temperature?

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A. Wet-bulb temperatureis the temperature of humid air  you can think of it as one element of the weather. 

Wet-bulb temperature is an important indicator for both our health and the planet's environment. Once it reaches 35°C, or 95°F, humans reach their survival limit. That's why understanding wet-bulb temperature matters so much when it comes to global warming. 

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Q. Why Does Wet-Bulb Temperature Matter?

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 ◎ Impact on Human Health

When wet-bulb temperature is high, our bodies struggle to cool down through sweat, which can lead to serious health problems like heatstroke. 

Humans actually have a kind of superpower: sweating. As the temperature rises, sweat droplets emerge from our pores and evaporate, cooling the skin and giving us a built-in cooling mechanism that keeps our bodies from overheating.

But that superpower has a theoretical ceiling. When the air is too humid, sweat can't evaporate properly, so the body can't cool itself down. That's exactly the state we call high wet-bulb temperature. 

Once wet-bulb temperature hits 35°C, the body's cooling system reaches its limit. At that point, even the healthiest person with unlimited access to water can't survive more than a few hours.

 ◎ Impact on Ecosystems and the Environment 

Wet-bulb temperature also has a major impact on ecosystems and the environment. High wet-bulb temperatures affect plant and animal habitats and hurt crop growth. Hot weather also drives up energy demand, putting even more strain on the environment.

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Q. How Is Wet-Bulb Temperature Measured?

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 ◎ How It's Measured

The way wet-bulb temperature is measured is actually pretty interesting. Scientists use a special tool called a wet-bulb thermometer.

The device is made up of two thermometers: a "dry-bulb thermometer" that measures the plain air temperature, and a "wet-bulb thermometer" whose tip is wrapped in a wet cloth.

As air passes over the wet cloth, the water evaporates and pulls heat from the surroundings, cooling down the wet-bulb thermometer's reading. That resulting temperature is the "wet-bulb temperature."

Image source: ClimateCheck

◎  Reading the Numbers

A wet-bulb thermometer tells you exactly how hot and humid the air really is. That matters most in hot regions like Delhi, India, where wet-bulb temperature—not just air temperature—has an outsized effect on the local ecosystem.  

Let's take a look at recent summer wet-bulb temperatures in Delhi:

▶ June 29, 2022, wet-bulb temperature: 33.7°C (Source: Hindustan Times)

▶ July 16, 2022, wet-bulb temperature: 36.2°C (Source: Hindustan Times)

The human survival-limit wet-bulb temperature is 35°C. Those numbers give a sense of just how hot and humid Delhi's summer really was. In the summer of 2022, high wet-bulb temperatures in Delhi killed more than 160 people. 

▲ In the summer of 2022, wet-bulb temperatures in Delhi exceeded the human survival threshold of 35°C, killing more than 160 people. 

Photo source: Getty Images Plus

And it hasn't stopped there. In May 2024, a heatwave in Sindh Province, Pakistan killed more than 568 people, and in 2025 a prolonged heatwave across India and Pakistan from April through July exposed hundreds of millions of people to extreme heat stress. 

In November 2022, the World Bank announced that parts of India could become uninhabitable for humans in the future. 

This kind of heat also hits ecosystems hard. High wet-bulb temperatures are expected to deal a serious blow to India's farming and livestock industries before long, making water harder to secure, degrading soil, and driving down agricultural output.

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Q. How Are Climate Change and Wet-Bulb Temperature Connected?

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 ◎ The Effects of Global Warming

Global warming is pushing up average temperatures worldwide, and that's driving wet-bulb temperatures up right along with it. 

A 2020 Columbia University study found that the planet is already experiencing combinations of heat and humidity that threaten human life.

India is the hardest hit. Analyzing global weather data collected from 1979 to 2017, the Columbia University research team found that hotspots along India's eastern coast and in northwest India recorded the highest wet-bulb temperatures on record—in the 99.9th percentile (at least 31°C).

And it's not just India. Take a look at the map below and you'll see Pakistan and northwest India, the Red Sea coast, the Gulf of California, and the southern Gulf of Mexico coast marked in red (at least 33°C) and yellow (at least 31°C).

▲ Extremely high wet-bulb temperatures are being observed worldwide. Areas shown in yellow and red recorded daily wet-bulb temperatures of at least 31°C. 

Source: Science Advances

 ◎ Future Climate Projections

In 2021, the UK's Met Office, the UK's national weather and climate research agency, released a set of future projections based on rising global temperatures. According to the scenarios, if global warming continues on its current path, the number of people facing life-threatening extreme heat stress will climb sharply. 

According to the Met Office, if global temperatures rise by 2°C, the number of people worldwide affected by extreme heat stress would grow from today's 68 million to roughly 1 billion. 

Push that further—if global temperatures rise by 4.0°C, roughly 50% of the world's population is projected to live in regions affected by extreme heat stress. 

Here's the thing: this isn't just a future scenario anymore. That 2021 projection is already unfolding. A joint WHO and WMO report released in August 2025 found that we don't need to wait for the future—it's already happening right now. Some 2.4 billion people, or 71% of the global workforce, are already exposed to excessive heat, which kills roughly 19,000 people and causes 22.87 million occupational injuries every year.

▲ 2.4 billion people—71% of the global workforce—are already exposed to excessive heat, causing roughly 19,000 deaths every year. Source: WHO/WMO, Climate Change and Workplace Heat Stress (Aug 2025)

 ◎ Europe Isn't Safe Anymore Either

This crisis isn't just a South Asian story. Europe, long thought of as having a mild climate, has recently seen some alarming developments of its own. In June 2026, Europe endured what's considered its worst heatwave on record. According to the World Health Organization (WHO), more than 1,300 excess deaths were recorded across Europe in just over a week starting June 21, and temperatures in Andújar, in southern Spain's Andalusia region, hit 45.1°C. France recorded its hottest day since records began in 1947 (44.3°C), while Germany, Czechia, and other countries also broke their national temperature records.

Europe has its own particular vulnerability: only about 20% of homes have air conditioning, and most housing was built to keep the cold out, not the heat. WHO Director-General Tedros Adhanom Ghebreyesus warned that "Europe is the fastest-warming continent on Earth," adding that "heatwaves that used to happen once every 300 years now occur more often than once a decade." In 2025 alone, roughly 24,400 people died from heat-related causes in Europe, and a study found that 68% of those deaths—about 16,500—were directly attributable to climate change (London School of Hygiene & Tropical Medicine and Imperial College London, Sept. 2025).

Dr. Andy Hartley, Head of Climate Impacts at the Met Office, warns: "People living in wet-bulb temperatures above 32.0°C face extreme risk. Vulnerable groups and outdoor workers face even greater risks to their health. Today, this figure is being reached in a number of regions, such as parts of India, but our analysis shows that with a 4.0°C rise, extreme heat risk could affect people across most of the world's continents."  

▲ This map shows where wet-bulb temperatures above 32.0°C would occur for 10 or more days a year if global temperatures rose 4.0°C above pre-industrial levels.

Source: Met Office

Purdue University climate scientist Professor Matthew Huber has issued a similar warning, saying "extreme conditions where the wet-bulb temperature reaches 35°C could become much more common by the end of this century."

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We Need to Act!

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These research findings and warnings from scientists about rising wet-bulb temperatures show just how serious climate change's impact on humanity really is. 

If temperature and humidity keep rising at this rate, this blue planet we love will become an increasingly difficult place for life to survive. 

Tackling global warming and rising wet-bulb temperatures requires strategies tailored to each region and country. But that alone isn't enough. It's time for all of us to act.

By this point you might be thinking, "what difference does recycling or saving electricity really make?" Fair enough. Individual action alone can't stop this crisis. So we've split what we can do into two tracks: one is protecting someone's life right now, and the other is slowing down how fast the planet keeps heating up.

1. Right Now: Look Out for the People Around You

✓ When a heat advisory is issued, check in on elderly neighbors who live alone

✓ Remember that outdoor workers need water, shade, and rest breaks

✓ Use local cooling shelters, and let others know they exist

2. Starting Today: Slow the Warming

✓ Recycle actively

✓ Choose sustainable products

✓ Turn off electronics you're not using

✓ Take public transit, bike, or walk instead of driving

One small action could save someone facing a heat crisis today, or help lower the temperature our children will inherit. This is what we need to do, and what we can do, right now. 

Written by Sharon Choi

Director of Planning

Sunhak Peace Prize Secretariat