July nights in downtown Charleston offered almost no cooldown after the day's intense heat.
The city center repeatedly set record-high overnight lows, underscoring that climate-related warming is erasing the nighttime respite people rely on to recover.
What's happening?
The Post and Courier reported that temperatures in the heart of the city stayed abnormally high after sunset during a notable run of record-warm nights.
With a typical July nighttime temperature of 77 degrees, downtown Charleston still saw overnight lows reach 82 to 84 degrees on eight record-setting dates, a tally 25% higher than the previous five years combined.
National Weather Service data indicates that, before this summer, downtown Charleston's standing record warm nighttime lows all dated to before 2000.
According to meteorologist Michael Stroz, the warm nights stem from a mix of regional climate influences and local development.
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A very strong El Niño in the Pacific is contributing to hotter conditions in the Southeast, and urban materials such as asphalt and concrete store heat during the day before releasing it after dark.
The result is a clear urban heat island, with the built-up downtown area staying much warmer at night than nearby places with more trees and less development.
Why does it matter?
The danger of high overnight temperatures goes beyond discomfort. Without a cooler period after sunset, the body has less opportunity to recover from daytime heat, increasing the chances of heat-related illness, particularly during long hot stretches.
The National Weather Service ranks extreme heat as the deadliest weather hazard in the United States.
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In South Carolina, the most recent S.C. Department of Public Health figures show 713 heat-related emergency room visits in July 2024, the state's July peak.
For households already squeezed by higher living costs, even using air conditioning can become a difficult choice, leaving the people most at risk — older adults, children under the age of five, and people with chronic illnesses — especially exposed.
Their effects also show up in sleep. From 2020 to 2025, the average person lost about 56 hours of sleep each year to high temperatures, with roughly six of those hours attributable to rising global temperatures.
What can I do?
Forecasters are paying closer attention to overnight heat as it becomes a more visible part of summer weather. Nighttime lows can be just as important as daytime highs when officials decide whether to issue heat alerts or advise residents to take precautions.
Reducing planet-warming pollution and building cooler communities can help. More tree cover, additional shade, and surfaces that absorb less heat can all reduce the amount of warmth that lingers in paved areas after sunset.
Immediate safety measures include using air conditioning when possible, staying hydrated, limiting strenuous activity in the evening, and checking on neighbors who may be more vulnerable to heat.
Closing blinds during the day and seeking out libraries, community centers, or other cooled indoor spaces can also help.
Access to relief is uneven: U.S. Census Bureau data shows roughly 22,600 South Carolina households lack air conditioning.
Charleston's July shows that rising heat is no longer just a daytime threat. When the sun goes down and temperatures still do not ease, the risks to sleep, health, and daily life can persist around the clock.
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