In the past year alone, record-breaking heatwaves across the globe have reignited the conversation around rising temperatures and their direct impact on human survival. Scientists are increasingly raising concerns over a relatively lesser-known measure that could redefine our understanding of heat’s danger: the wet-bulb temperature (WBT). This metric combines humidity and dry temperature to gauge heat stress on the human body, and it’s edging closer to becoming a critical factor in our daily lives.
Understanding the Wet Bulb Temperature
The wet-bulb temperature is a measure derived by wrapping a wet cloth around a thermometer bulb and allowing the water to evaporate. Evaporation causes cooling, so the resultant reading is always below the dry-bulb temperature unless the air is fully saturated with moisture. If the air has high humidity, less water evaporates, keeping the temperature closer to the actual air temperature.
For instance, a dry-bulb temperature of 40°C with a relative humidity of 75% yields a wet-bulb temperature close to 35°C. The importance of this measure lies in its ability to illustrate how the human body can cool itself via sweating. Above the wet-bulb temperature, our body loses its ability to sweat efficiently and thus struggles to prevent a dangerous rise in internal body temperature.
The Threshold of Human Survivability
The generally accepted “critical” WBT threshold for human survivability is 35°C. At this point, a healthy individual can only withstand conditions for up to six hours before the body’s core temperature rises to fatal levels. However, recent research from Pennsylvania State University suggests that the actual survivability threshold may be lower, at around 31.5°C, thus exposing far more people to extreme heat than previously believed.
It’s crucial to recognise that wet-bulb temperatures below this threshold are still dangerous for certain vulnerable populations like the elderly, children, and those with pre-existing health conditions. Heat exhaustion and heatstroke can occur at much lower wet-bulb temperatures, particularly in places without adequate cooling infrastructure.
How Climate Change Exacerbates Wet-Bulb Extremes
The surge in WBTs is closely linked to the ongoing climate crisis. For every 1°C rise in average global temperatures, the wet-bulb temperature can increase by the same margin. Thus, limiting global warming to 1.5°C above pre-industrial levels could significantly reduce the regions reaching the critical 35°C mark.
Heatwaves are worsening faster than any other type of extreme weather event due to the rise in greenhouse gas emissions. In the recent heatwave in India and Pakistan, which affected over a billion people, studies suggest climate change made such events 30 times more likely.
Global Impact of Rising Wet-Bulb Temperatures
Regions around the Arabian Gulf, such as Pakistan, India, and Saudi Arabia, are on the frontline of the WBT crisis. For instance, some coastal subtropical areas have already recorded WBTs of 35°C, albeit briefly. Across the globe, occurrences of WBTs above 30°C have more than doubled since 1979, with countries like Mexico and Australia also seeing record highs. Iraq saw temperatures reach 53°C in 2020, illustrating that these are not isolated events.
Even countries like the UK and France, where historical data shows a relatively mild climate, are experiencing higher wet-bulb temperatures. In the UK, a previously unthinkable 40°C dry temperature was recorded in 2022, and WBTs exceeding 31°C are now considered possible.
Why the Wet-Bulb Temperature Matters for Public Health
High WBTs pose a severe risk to public health. As our bodies fail to cool themselves effectively through sweat, the risk of heat-related illnesses like heatstroke increases. Dehydration, organ failure, and death are possible if people do not find ways to escape the conditions. The elderly, those with chronic illnesses, and outdoor workers are particularly vulnerable.
Furthermore, buildings are not always equipped to handle extreme heat, especially in areas where air conditioning is not common. Heatwaves frequently cause spikes in emergency calls and lead to overwhelmed hospitals. Therefore, preparing communities for high WBTs is crucial, and understanding how to calculate them is the first step. Use the wet-bulb calculator to measure this in your region and adjust your activities accordingly.
Economic Consequences of Rising Wet-Bulb Temperatures
The economic implications of rising WBTs are also significant. Labour productivity plummets as outdoor work becomes more hazardous, impacting agriculture and construction. Extreme heat can also damage infrastructure, with roads and rail tracks buckling under high temperatures.
Tourism may also be affected, as popular destinations experience conditions that make travel less attractive. Businesses and individuals must adapt to the new normal or face significant financial losses.
Policy Response to Wet-Bulb Extremes
Addressing this global issue requires comprehensive policy action, both locally and internationally. Governments need to establish heat action plans that include early warning systems, cooling centres, and public awareness campaigns. Investing in urban green spaces can provide natural cooling effects and lower temperatures in densely populated areas.
Internationally, collaboration on climate mitigation can reduce greenhouse gas emissions and curb global warming, thereby slowing the rise in WBTs. Limiting global warming to 1.5°C is crucial to prevent large swathes of the tropics from becoming uninhabitable.
Conclusion
As heatwaves intensify, the importance of understanding and mitigating the wet-bulb temperature’s impact on human health and economic stability becomes evident. This measure, which combines heat and humidity, presents a growing challenge as we inch closer to the limits of human survivability. By staying informed and utilising resources like the wet-bulb calculator, we can take proactive steps to safeguard our health, livelihoods, and communities from this growing threat.
