A study examining records from more than 1,200 U.S. weather stations since 1899 found fewer extreme cold events and no significant nationwide increase in extreme heat, challenging the perception that temperature extremes have steadily worsened over the past century.
By yourNEWS Media Newsroom.
A century-spanning analysis of original temperature records from more than 1,200 weather stations across the United States has concluded that the nation has not experienced a significant long-term increase in extreme heat and has instead seen an overall moderation of both hot and cold temperature extremes.
The study, published this spring in the academic journal Theoretical and Applied Climatology, was conducted by climatologist John Christy, formerly of the University of Alabama. His research examined weather observations dating to 1899, including historical records that he said are absent from commonly used federal datasets.
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Christy’s findings differ from the widespread perception that extreme high temperatures have become increasingly common across the United States.
“We have the systematic measurements in the United States that show the extremes of the [19]20s, 30s and 50s in terms of heat were much greater than the ones currently,” Christy told The Epoch Times.
“Even when you include the western parts of the country that are having their ‘1930s’ today, the rest of the country is not following the script.
“On balance, you don’t have a countrywide extreme event.”
Christy’s analysis does not dispute that average temperatures have increased. Instead, it focuses on a different measurement: the hottest and coldest temperatures recorded during the warmest and coldest parts of the year.
The National Oceanic and Atmospheric Administration has stated that average temperatures have risen approximately 2 degrees Fahrenheit since 1850 and that the increase has accelerated during the past several decades.
NOAA has also identified 2024 as the warmest year in the global temperature record dating to 1850 and said all 10 of the warmest years in that record occurred between 2015 and 2024.
The agency attributes the long-term increase primarily to greenhouse gas emissions produced by human activity.
“Earth’s average surface temperature has been rising because human-produced greenhouse gases are causing Earth to absorb more energy than it radiates back to space,” NOAA has stated.
Christy examined the historical record from another perspective.
Rather than using annual averages as the primary measure, he analyzed temperature extremes, which he argues are particularly important because they establish the “environmental boundaries” within which plants, animals and people live.
His results indicate that extreme high temperatures occurred more frequently during earlier portions of the 20th century, particularly the 1930s, while extreme cold temperatures have become less common.
That decline in severe cold, Christy argues, has been a major contributor to the rise in average temperatures.
A central part of his work involved recovering observations that had been excluded from federal datasets through quality-control procedures.
NOAA uses algorithms to identify measurements that might be erroneous or affected by factors unrelated to broader climate conditions, including changes in station locations or instrumentation.
Christy instead returned to original weather reports, including handwritten records created by the Army Signal Corps and Weather Bureau as well as later observations taken by military and federal agencies.
Those records are part of the historical network now maintained by NOAA.
Christy said his interest in reconstructing the original data intensified when information in federal databases conflicted with temperatures he remembered from regions he knew personally.
“When I was going through the federal data that’s digitized, I noticed that the government’s website says the hottest temperature in Newport, Oregon, in history was 94 degrees,” Christy said. “I knew a lot more about the West Coast because I grew up there.”
He then examined Newport’s original handwritten records.
Christy said he found a temperature of 100 degrees recorded in June 1925 as well as 10 additional days when the temperature exceeded 94 degrees.
He subsequently applied the same approach to records from more than 1,200 stations nationwide.
To determine whether unusually high or low readings were errors, Christy compared them with measurements from surrounding weather stations. If nearby stations recorded comparable conditions, he treated the observation as valid.
“This takes a tremendous amount of manual intervention, and that is something we just don’t have today because everything’s done with AI or a computer algorithm,” he said. But without the original data, “you can’t quite get the true nature of climate and the type of rapid extremes that truly occur.”
“My data set is far more complete than what the federal government provides to scientific researchers,” Christy said.
NOAA public affairs supervisor Monica Allen defended the agency’s methods while declining to evaluate Christy’s conclusions directly.
“NOAA does not comment on the findings of external studies,” Allen said, adding that “NOAA uses scientifically vetted quality assurance algorithms to identify and flag potentially erroneous observations and to detect abrupt changes in a station’s historical data that might be driven by non-natural factors, such as a station move or instrumentation change.”
“NOAA also receives input from our users to identify, review, and document erroneous observations in historical datasets,” Allen told The Epoch Times.
By returning observations removed through those procedures to his dataset and concentrating on extremes rather than annual averages, Christy found that the 1930s contained the greatest concentration of extreme high temperatures.
His analysis found no significant nationwide increase in extreme heat since the beginning of the record and a substantial reduction in extreme cold.
Christy also identified a pronounced difference between daytime and nighttime warming.
Most of the temperature increase he observed occurred overnight, while daytime temperatures showed relatively little long-term change.
“Nighttime temperatures have soared in the past 120 years,” Christy said.
He argues that the pattern raises questions about how much of the measured increase at some weather stations may be connected to development surrounding the stations rather than greenhouse gases alone.
“That is due to human development around the weather stations because nighttime temperatures are far more sensitive to urbanization—parking lots, buildings, removal of forests and so on—than daytime temperatures.”
Many weather stations that were once located in rural areas have gradually become surrounded by suburban development, pavement, buildings and other infrastructure.
Asphalt, concrete and other constructed surfaces can absorb solar energy during the daytime and release stored heat after sunset. Development can also remove trees and vegetation that once provided shade and cooling.
“You can’t pin it on greenhouse gases alone because the urban effect is so obvious in these stations,” Christy said. “It doesn’t take much to make an urban heat island—you can just build a parking lot next to a rural station, and you’ve got an urban heat island started.”
Christy said temperature trends also vary significantly by region.
Western states are currently experiencing more frequent heat waves, he said, while extreme heat in much of the eastern United States is less prevalent than it was during portions of the 20th century.
Focusing on the areas experiencing the most intense heat at a particular moment can therefore create an impression that temperature extremes are increasing everywhere simultaneously, he argued.
Christy has studied weather and climate for decades.
His interest began as a teenager growing up in Fresno, California, and continued while he studied mathematics in college.
After graduating, he helped establish weather stations in Africa before earning a doctorate in climate dynamics from the University of Illinois. He later spent decades teaching atmospheric science at the University of Alabama.
Christy and co-author Roy W. Spencer received NASA’s Medal for Exceptional Scientific Achievement in 1991.
The American Meteorological Society honored them in 1996 “for developing a global, precise record of earth’s temperature from operational polar-orbiting satellites, fundamentally advancing our ability to monitor climate.”
Christy also contributed to Intergovernmental Panel on Climate Change reports during the 1990s.
“I can go back to records I recorded 60 years ago,” Christy said, “so in a sense, I’ve experienced a whole lot of climate in my life firsthand.”
Publishing his latest research proved difficult, Christy said, with reviewers repeatedly challenging aspects of the study before it was accepted.
“The reviewers tried to find anything they could to reject it, and fighting that takes a long time and a lot of effort,” Christy said.
“I had to overcome many objections, and I had to do some convincing by repeatedly going through a process of showing, ‘This is your objection, I have tested your objection, it’s incorrect.’
“There have been other papers we just never could get published. “That’s unfortunate because that means the world does not have a chance to see the results of this kind of research.”
Christy said he does not expect the study necessarily to resolve broader disputes over climate change because opinions on the issue can be deeply entrenched.
“If your political view is that extremes are getting worse and worse, that’s almost a religion, so you can’t really change minds on that,” Christy said.
“But if you’re someone who’s just dispassionately looking at information, my role in the past 50 years has been to build data sets the best I can so that we can ask questions of the data sets about these very kinds of issues.”
NOAA, meanwhile, makes large quantities of weather observations available for scientists to analyze using independent methodologies.
Allen said the agency uses its nClimGrid-Daily program to evaluate observations derived from the Global Historical Climatology Network-Daily dataset.
“This data set uses a broad set of daily stations in its analysis of US temperatures, and allows NOAA, the user community, and the science community to examine the full breadth of our data,” Allen said.
She said average and extreme temperature measurements serve different but complementary scientific purposes.
“Average temperatures establish the historical baselines used to identify extreme conditions; extreme temperatures help address risks resulting from events such as heat and cold waves,” Allen said.
Christy nevertheless contends that academic researchers who challenge dominant interpretations of climate trends can face obstacles obtaining research funding and publishing their findings.
“On an issue like climate change, it’s about as intolerant as they come,” he said.
“But I’m grateful to be here in Alabama where you still have the ability to ask questions and to examine the real data and not be fired for it.”
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