When Will Extreme Heat Become Unlivable?

Brief Summary

This video discusses the increasing threat of extreme humid heat waves, also known as wet-bulb events, which are becoming more frequent and dangerous due to climate change. It explains the science behind wet-bulb temperatures, their impact on the human body, and the limitations of air conditioning as a solution. The video also touches on the importance of transitioning to clean energy and implementing urban design strategies to mitigate the effects of extreme heat.

• Humid heat waves are potentially deadlier than dry heat waves.
• Wet-bulb temperature is a measure of both heat and humidity, indicating when conditions become lethal.
• Air conditioning, while helpful, is not a perfect solution due to cost, energy consumption, and potential grid overload.
• Transitioning to clean energy and rethinking urban design are crucial for mitigating the impact of extreme heat.

Intro

The video introduces the rising threat of extreme humid heat waves, or wet-bulb events, which are becoming more frequent and dangerous due to climate change. These events, characterized by high temperatures and oppressive humidity, can overwhelm the human body's ability to cool itself. The video highlights a study indicating that many populated areas could experience these conditions with just two degrees Celsius of global warming, emphasizing the urgent need for effective cooling strategies.

Dry vs. Humid Heat

The video explains the difference between dry and humid heat waves. Dry heat waves are typically caused by high-pressure systems that trap hot air near the surface, as seen in the 2003 European heat wave and the 2021 Pacific Northwest heat dome. Humid heat, on the other hand, occurs when rising temperatures increase the amount of moisture the atmosphere can hold, leading to higher humidity levels. The 2015 Karachi, Pakistan heat wave, where temperatures reached 45 degrees Celsius with high humidity, power outages, and water shortages, resulted in at least 1,200 deaths in just 10 days.

Understanding Wet-Bulb Temperature

The segment explains wet-bulb temperature, which combines heat and humidity into a single metric to assess dangerous conditions. It uses the analogy of a thermometer with a wet sock to illustrate how evaporation cools the surface, similar to how human skin cools through sweat. The effectiveness of this cooling process decreases as humidity increases, making it harder for the body to regulate its temperature. Research on the human body's limits in humid heat is challenging due to the dangers involved, but studies aim to identify the thresholds at which the body can no longer compensate.

Limits of Compensability

The video discusses the concept of the "limit of compensability," where the human body can no longer regulate its core temperature through sweating. Uncompensable wet-bulb temperatures range from about 19 to 32 degrees Celsius. A 19-degree Celsius wet-bulb is equivalent to 46 degrees Celsius with low humidity or 32 degrees Celsius with high humidity. This threshold varies based on factors like activity level, air temperature, humidity, and age, with older adults being more vulnerable due to less efficient thermo-regulatory responses and higher risks of comorbidities.

Global Impact and Future Projections

The video projects the global impact of rising temperatures, noting that at two degrees Celsius of global warming, about a third of Earth's land area, including populous regions in India, China, and the eastern U.S., could face uncompensable wet-bulb temperatures. If warming reaches four degrees Celsius, over 60% of Earth's landmass could experience these dangerous conditions. The 2003 European heatwave, which caused thousands of deaths, did not reach these dangerous wet-bulb thresholds, but the 2015 Karachi heat wave did. At two degrees Celsius of warming, these thresholds could be crossed for younger adults as well, and at four degrees, they could be crossed for older adults for most of the heat wave's duration.

The Role and Limitations of Air Conditioning

The video emphasizes that once critical wet-bulb thresholds are crossed, the only way to lower body temperature is by cooling the environment, making air conditioning a crucial adaptation measure. However, AC is not a perfect solution due to its high cost, energy intensity, and the fact that it transfers heat outside, potentially worsening the urban heat island effect. Widespread AC use can also strain power grids, leading to outages that put vulnerable populations at greater risk, especially when compounded by other extreme weather events like hurricanes.

Paradox of Air Conditioning and Alternative Solutions

The video addresses the paradox that increased reliance on air conditioning can exacerbate global warming, as AC units currently account for about 3% of global greenhouse gas emissions. The number of AC units worldwide is expected to nearly triple by 2050, leading to a massive rise in energy demand. To address this, the video advocates for transitioning to clean energy to power AC without accelerating climate change. Additional solutions include rethinking urban design with white or green roofs, planting trees, building more cooling centers, upgrading electrical grids, and prioritizing the protection of vulnerable populations during heat waves.