Springs are getting warmer across the United States, and a new scientific analysis shows that human activity is the main cause. Researchers from Climate Central examined spring temperature data from 241 major U.S. cities between 1970 and 2025 to understand what is driving these changes.
The key finding is dramatic. In 98 percent of cities studied, human-caused climate change was the leading driver of spring warming. This means that more than half of the warming observed in these cities can be directly linked to human activities. The sample size of 241 cities provides strong evidence because it covers locations across the entire country, making the results reliable and meaningful.
The researchers used something called the Climate Shift Index to determine causation rather than just correlation. Correlation means two things happen together, while causation means one thing actually causes the other. By comparing computer models of our current climate with models showing what temperatures would be like without human influence, scientists could prove that human activities are causing the warming, not just happening at the same time.
The analysis also considered confounding variables, which are other factors that might affect the results. These include natural climate patterns like El Niño and practical issues such as weather stations being moved to new locations over the decades. Even after accounting for these confounding variables, human-caused climate change remained the primary explanation for spring warming in nearly all cities.
Since 1970, spring temperatures have increased by an average of 2.6 degrees Fahrenheit across the cities that showed warming. The warming was most severe in the Southwest, where temperatures rose 3.4 degrees on average. Reno, Nevada experienced the most dramatic change at 6.9 degrees warmer.
This warming brings real consequences. Most cities now experience at least seven additional warm spring days compared to the 1970s. These changes extend allergy seasons, increase wildfire risk, reduce water supplies from melting snow, and help disease-carrying mosquitoes survive longer.