Heat continues to build across the Deep South and Texas Gulf Coast, where the hot temperatures have combined with high humidity. Image: SSEC/RealEarth/University of Wisconsin at Madison

Daytime highs across much of the Southern United States have been breaking records this past week but a stifling combination of high heat and humidity is preventing nights from cooling off, creating dangerous heat situations in cities like Houston (also neighboring Galveston where the heat index remained above 100 for 40 straight hours). As the Washington Post explained, greater atmospheric moisture which is a symptom of climate change plays a major role in warming overnight lows faster than daytime highs. Consider this: Between 1950 and 1990, Hobby Airport, just south of downtown Houston, saw 22 days total with nighttime lows at or greater than 80 degrees. Since 1990 — 29 years — the same airport has seen 130 days with nighttime lows at or above 80 degrees.

Rising Humidity: As global average temperatures rise, so does the amount of moisture in the air. More heat + more humidity means the effects of heatwaves will become magnified as our planet continues to warm, pushing people and cities to the brink. Hot, humid days are also a lot more dangerous for people because, as Seeker explained, “air crowded with water molecules stops sweat from evaporating from then skin, impairing the body’s own ability to cool itself. When the human body is deprived of this natural cooling system, organs can strain and begin to fail, resulting in lethargy, sickness, and even death.”

Hot Reality: The Washington Post noted that water temperatures in the Gulf of Mexico are running between 1 and 2 degrees above average which adds even more water vapor to the air. Atop an environment that’s already warming because of climate change, these oppressive heat waves are becoming and will continue to be increasingly common in the years ahead. In addition to climate change, urbanization and an increase in heat-absorbing surfaces in these areas are contributing to warmer nights.

Why This Matters: Not only is extreme heat becoming more prevalent but it doesn’t affect all residents of a city in the same way. As the New York Times recently reported, “new research shows that temperatures on a scorching summer day can vary as much as 20 degrees across different parts of the same city, with poor or minority neighborhoods often bearing the brunt of that heat.” White cities can plant more trees and take measures to heatproof, the best way to ensure that dangerous heat and humidity don’t claim needless lives is to drastically reduce global greenhouse gas emissions and limit the effects of climate change.

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