Researchers at two Spanish universities have found that 84% of the contiguous U.S. states has shown signs of warming over the last 70 or so years, which is more than previously suggested.
In a report published last week in the journal PLOS Climate, the researchers found that 41 U.S. states have gotten warmer since the middle of the last century. Alaska and Hawaii weren’t included in the study.
The states’ warming patterns weren’t uniform, Jesús Gonzalo, an economist and professor at the University of Charles III in Madrid, explained using a riddle. In Spain, the satirical statistics joke goes: “There are two hungry people vying over a single chicken. One eats the entire thing, leaving the other to starve. So, on average, each person has eaten half of a chicken.”
In that scenario, the average amount of food consumed per person failed to convey the important fact that 50% of the pair whose chicken intake was being calculated had nothing to eat at all.
“The average doesn’t say much, no?” Gonzalo said.
Its premise exemplified the main conclusion of the report that Gonzalo co-authored, which urged researchers and policymakers to look beyond mathematical averages when evaluating how temperature trends relate to climate change.
In the report, Gonzalo and his co-author, María Dolores Gadea Rivas of Spain’s University of Zaragoza, wrote that although “the climate system functions on a global scale, its effects are experienced locally, resulting in significant regional variability.”
To detect variations, they analyzed tens of thousands of daily temperature readings collected across the contiguous U.S., some of which dated back to 1950.
The data showed that the effects of climate change on temperature are existent and measurable in a larger swath of the U.S. than previously thought, since a fair amount of climate research quantifies those effects using averages. Also referred to as the arithmetic “mean,” an average is calculated by adding together a certain batch of values — temperatures recorded in the state of California, for instance — and dividing that by the number of values included in that sum.
Averages are meant to generally reflect the tendencies of values involved in their calculations. But they don’t always provide a complete picture, according to Gonzalo, who says relying on them can be misleading in some instances.
“The U.S. is maybe one of the countries with the most heterogeneous climate. And the main message is, if you want to measure heterogeneity, don’t use the average,” Gonzalo said. “If you pay attention to the average, you can make a mistake.”
Gonzalo’s new climate report argued that focusing exclusively on average temperatures, and how they have or haven’t increased over time, can have serious pitfalls for climate scientists and anyone involved in climate policy.
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The study found that average temperatures rose in 27 U.S. states between 1950 and 2021, corroborating earlier research. But they also increased significantly in 14 more, which, Gonzalo noted, is a huge difference that could potentially alter the country’s approach to addressing the issue.
“This is consequential when you try to design more efficient mitigation and adaptation policies,” he said.
Instead of averages, the report examined the full range of temperatures in a given state, from lowest to highest, and tracked them over time — the same way one might consider the full range of incomes in a particular place to accurately understand its wealth distribution and progress. The report brought to light what its authors described as “previously hidden patterns” of warming in every corner of the nation.
Western states, including California, Idaho, Nevada, Oregon, Washington and Wyoming, saw the largest increases in their highest temperatures, while Central states, like Iowa, Minnesota, Montana, Nebraska and the Dakotas saw relatively greater jumps in lower temperatures than higher ones over the years, the researchers found.
Northern states, across the upper Midwest, Northeast and Northwest, saw similar increases across the whole of their temperature ranges, meaning that cooler temperatures and warmer temperatures rose at comparable paces.
All of those trends appear to be accelerating, Gonzalo said, and tailoring public response strategies to realistically fit the scope of the situation at hand could be especially beneficial.
The anomalous “warming hole”
The only U.S. states that haven’t shown statistically significant signs of warming are Texas, Oklahoma, Mississippi, Alabama, Georgia, Kansas and Arkansas, the report said.
That list of states in the central and southern U.S. is consistent with a known phenomena called a “warming hole.” It describes a region that hasn’t experienced rising temperatures despite climate change. Scientists have long considered it an anomaly.
Research has suggested that counterintuitive cooling in that area could be induced by aerosols, changes in land use or the water cycle, which may have intensified in certain places as a response to greenhouse gas emissions, according to the National Oceanic and Atmospheric Administration.
The NOAA said in 2023 that additional studies should be done to answer some of those questions.
