From coast to coast, heat enveloped the United States for nearly a week, flushing weather maps with shades of red. On July 4, about half of all Americans were under extreme heat warnings. The trend continued through the holidays and into the next week, shattering temperature records in cities across the United States.
Wednesday, approx 140 million Americans, more than a third of the country, remained under active National Weather Service extreme heat advisories, watches and warnings. A heat risk map released by federal agencies showed the worst conditions were along each coast, marked by regions of color-coded severity. On the West Coast, states from Washington to Arizona were awash in deep burgundy—extreme risk. Along the East Coast, states from Maine to Florida were spotted with scarlet — high risk.
“There’s not a lot of relief in sight,” said Zach Taylor, a meteorologist with the National Weather Service. In fact, the heat on both coasts may continue into mid to late July. “This is a very dangerous and serious situation that people should not take lightly.”
On Sunday, Las Vegas topped 120 degrees Fahrenheit, eclipsing the city’s 2017 record by 4 degrees. By Tuesday, roads in Washington DC were reeling as the city hit 110 degrees F, and daily record highs were set in Seattle and across the Pacific Northwest.
The Centers for Disease Control and Prevention Heat and Health Tracker shows an increase in heat-related emergency room visits in the hardest-hit areas. This time last year, similar temperatures took over 645 lives only in Arizona’s Maricopa County, home of Phoenix, where the thermostat hovers around 110 degrees F for a month.
These dangerous conditions are the continuation of climate trends, after more than a year of record temperatures. Worldwide was the last 13 months the hottest ever recordedand the past 12 months have passed 1.5 degrees Celsius of warming above pre-industrial temperatures – a predictable climate milestone.
According to Taylor, these heat waves are particularly notable in intensity and length—characteristics associated with human-caused planetary warming. Studies have shown that climate change is creating heat waves that are more frequent intense, linger longer, and move more slowly.
Scorching temperatures are too fuel wildfires. When heat is coupled with low humidity and high winds, small ignitions can quickly grow into infernos. From 10 July the National Interagency Fire Center tracker showed there are 76 large active fires across the country, and almost all of them are in states under heat advisories. In Santa Barbara County, California, the Lake Fire ballooned into a 28,000-acre blaze, the largest the state has seen this year. In Southern and Central Oregon are officials ordering evacuation notices for multiple wildfires.
Cities are particularly dangerous because of the urban heat island effect, in which buildings and roads trap and amplify heat. In Phoenix, a hundred degree day can turn the asphalt into a 160-degree F grilland let those who touch it life-threatening burns. As temperatures rise, urban conditions are also ripe for a chemical reaction that creates ground-level ozone pollution, which can cause asthma and respiratory problems. Monday, New York state issued an air quality advisory after detecting this pollution at harmful levels.
And health threats don’t go away with the sun. In addition to the record daily temperatures, Taylor says, stagnant air can cause lingering highs overnight. “It can be just as, if not more, impacting health and heat stress because it doesn’t give the body the opportunity to cool down and recover at night.”
“Heat is an issue that is cumulative,” said Claudia Brown, a health scientist at the CDC’s National Center for Environmental Health. “So it’s not necessarily just a single hot day that leads to heat-related illness, but actually consecutive high temperatures,” Studies have shown that the risk of death connections with each successive day of heat, and increased night temperatures make it even worse.
And not everyone is at the same risk. “People who are older or young children tend to be more vulnerable because their bodies don’t thermoregulate as effectively,” Brown said.
Other factors, such as chronic health conditions and working outside, can also increase the chance and severity of heat illness. Because risks vary between neighborhoods, Brown recommends that those under heat advisories check the threat level in their specific zip code using the CDC’s online HeatRisk tool.
As temperatures are expected to simmer in the coming weeks, many local governments – such as Maricopa County in Arizona and Multnomah County in Oregon – provided cooling centers for people who may be homeless or have no access to air conditioning. Despite the busy summer season, the National Park Service also recommends that hikers visiting heat-beleaguered landmarks such as Death Valley and the Grand Canyonreconsider their plans.
