The study was conducted by a team of researchers at UC Santa Cruz, Clemson University, and the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory. Led by Claudie Beaulieu, associate professor of ocean sciences at UC Santa Cruz, the team analyzed multiple independent observational datasets of surface temperature spanning the period from 1970 to 2024. By applying advanced statistical modeling techniques to this wealth of data, the researchers were able to identify coherent spatial and temporal patterns in the way warming rates have shifted across the globe over more than five decades.

At the heart of the analysis is a technique known as changepoint detection, in which statistical models are fitted at each individual grid point on the planet’s surface to determine whether and when the underlying rate of warming has changed. This approach goes beyond simply asking whether global mean temperature is accelerating; it asks where on Earth those accelerations have emerged, and precisely when they began. The result is a kind of statistical map of the planet’s warming behavior, one that reveals the unevenness hidden beneath the smooth curve of the global average.

The most striking finding concerns the Northern Hemisphere’s mid-latitudes, where the most recent accelerations in warming are most prominent. Southeast China stands out as the region with the most pronounced changes in warming rate, followed closely by the Gulf of Mexico. The timing of these shifts is not uniform, however. According to the researchers, regional speed-ups have emerged in distinct waves, with onset timings ranging from the 1980s through the 2010s depending on the geographical area, a staggered pattern that underscores how differently the climate system is responding across space and time.

“What we wanted to do is provide a clearer, region-by-region picture of where warming is actually accelerating—and when it began,” said lead author Claudie Beaulieu, associate professor of ocean sciences at UC Santa Cruz. “Our study shows that regional speed-ups have emerged in distinct waves, with onset timings ranging from the 1980s through the 2010s depending on the geographical area.”

The new work builds on and extends previous research by members of the same team, which assessed whether an acceleration could be detected in global mean temperature. That global-scale question has become central to a lively scientific debate, as each successive year seems to shatter temperature records and as scientists grapple with whether the pace of warming itself is changing. The regional analysis, however, provides a far more nuanced picture. In addition to southeast China and the Gulf of Mexico, the team identified several other regions experiencing recent accelerated warming, including the eastern Mediterranean, Bolivia, the North Pacific, and New Zealand. The breadth of this list demonstrates that warming accelerations are not confined to any single climate zone or continent.

While the study focuses on statistically mapping these regional shifts rather than assigning definitive causes to each one, the researchers note that localized drivers may play a role in some, but not all, of the detected speed-ups. One particularly compelling clue lies in the timing of the changes. The onset timings detected by the team are consistent with declining sulfur-dioxide emissions from coal-fired power plants in China. Sulfur dioxide aerosols have a cooling effect on the atmosphere by reflecting sunlight, so reductions in aerosol pollution can unmask additional warming that was previously suppressed. This suggests that at least some of the dramatic acceleration observed in southeast China may be linked to the region’s dramatic improvements in air quality, although the researchers emphasize that pinpointing the physical mechanisms behind every regional speed-up will require further studies.

The methodological rigor of the study is central to its value. “Fitting our models at each grid point allows us to identify regions with similar warming behavior,” said co-author Rebecca Killick, professor of statistics at Clemson University and honorary professor at Lancaster University. “This is important for local communities to understand how increased warming will have local impacts.” By detecting changes in warming rates at such fine spatial resolution, the approach transforms an abstract global statistic into actionable, place-based information that communities, planners, and policymakers can use to assess their own exposure to a changing climate.

The implications of these findings extend well beyond academic debate. A key impact of warming accelerations is the shifting baseline for the frequency and severity of extreme events such as heatwaves. While continued steady warming alone causes this baseline to shift, any increase in the rate of warming can lead to a disproportionate increase in the likelihood of record-breaking events. In other words, when warming speeds up, the probability of unprecedented heat extremes does not merely rise in step—it can jump disproportionately, placing additional stress on infrastructure, agriculture, and human health. Identifying the specific regions and timings of warming shifts therefore provides crucial context for regional climate-impact assessments, adaptation strategies, and environmental planning.

The researchers also emphasize questions of equity and ecological vulnerability. Regions with large populations and low socioeconomic development are especially vulnerable to accelerated warming and the accompanying changes in temperature extremes, meaning that the regions identified in the study may face compounded risks. Ecosystems, too, are often more sensitive to rapid temperature shifts than to gradual changes, and the staggered timing of accelerations documented in the study could help ecologists anticipate where and when biological systems are most likely to be pushed past critical thresholds. “We hope that this work revealing when and where these accelerations have occurred in the past, along with an interactive public dashboard to enable the public to continue monitoring local rates of warming by clicking on a map, will provide tools and support to better anticipate localized impacts and target efforts where they are most needed,” Beaulieu said. The dashboard allows anyone to explore local warming rates directly, translating a sophisticated statistical analysis into a resource accessible to the general public.

Funded by the National Science Foundation through CAREER Grant AGS-2143550, the study represents a significant step forward in understanding the texture of global warming. By combining more than five decades of observational data from multiple datasets with sophisticated changepoint statistics applied at every point on the globe, the research moves the conversation about warming acceleration from a single global number to a rich, spatially resolved narrative. As record temperatures continue to make headlines and the debate over acceleration intensifies, this work makes clear that the answer to the question of whether warming is speeding up is neither a simple yes nor a simple no. It is a resounding yes in some places, at some times—and the where and the when matter enormously for the people and ecosystems living through them. The authors declare no competing interests, and the research was published in Nature Communications on September 22, 2026, under the title “Space-time signatures of surface warming accelerations since 1970.”

Subject of Research: Regional and temporal patterns of surface warming accelerations worldwide since 1970

Article Title: Unveiling the unevenness of global warming

Article References: Unveiling the unevenness of global warming. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: global warming, climate acceleration, surface temperature, changepoint analysis, southeast China, Gulf of Mexico, aerosol emissions, extreme heat events, regional climate, Nature Communications, climate adaptation, temperature datasets

Scientists have known for decades that extreme heat is becoming more frequent. Both the research record and lived experience across the world document that shift. What has been far less understood is when these events occur within the year. Most research on seasonal warming has concentrated on average temperatures or on shifts in the timing of the seasons themselves. Summer conditions in mid-latitude regions, for example, have lengthened by roughly six days per decade since 1990. But the timing of individual extreme heat events—a different question entirely—had received little if any rigorous attention. Extremes may not move in step with the seasonal average, and that disconnection is precisely what the new study set out to measure.

The researchers expected that rising global temperatures would uniformly make it easier to cross dangerous heat thresholds throughout the year, widening the extreme heat season symmetrically at both ends. That is not what they found. Instead, the expansion is lopsided. “In some places, we have a larger expansion of extreme heat during the spring, before the traditional heat season starts. In other places, there’s a much faster expansion of the heat season into fall,” Ivanovich explains. The asymmetry means that different regions of the world are experiencing fundamentally different transformations of their heat regimes.

The methodology behind the findings was deliberately careful. The team counted extreme heat events on the six inhabited continents between 1980 and 1989, defining “extreme” as days falling in the hottest 5 percent of daily temperatures. They performed this counting twice, using two distinct measures of heat. The first was standard thermometer readings, a measure of dry heat. The second was wet bulb globe temperature, a more sophisticated metric that combines humidity, solar radiation and air temperature to quantify heat stress as the human body actually experiences it. This distinction matters enormously: humid heat limits the body’s ability to cool itself through sweating, making it considerably more dangerous to people, while dry heat is harder on crops and ecosystems. Adapting to one is not the same as adapting to the other.

The authors then compared those 1980s baseline figures to the most recent decade in the record, 2015 through 2024. The results were striking. Extreme heat seasons had expanded significantly across just over half of the world’s land area for dry heat, and just under half for humid heat. In the western United States, eastern China, northern Africa and eastern Europe, extreme heat events became more common more rapidly in the two months following their historical heat seasons. The opposite held in western Europe, southern Africa and northwestern India, where extreme heat arrived predominantly in the two months before the traditional season began. “There are very clear asymmetries in how extreme heat seasons are expanding in different parts of the world,” Ivanovich says. “Extreme heat is starting to become something different in a lot of these regions.”

To be certain the pattern was real and not an artifact of a single dataset, the researchers ran their analysis with two independent sources—one compiled by NASA and the other by the European Centre for Medium-Range Weather Forecasts. The pattern largely held up across both. This kind of replication is essential when studying extreme events, which are by definition rare. Extreme heat outside its season is rarer still, which makes changes in its timing statistically difficult to pin down. Ivanovich emphasizes that the findings should be taken as a compelling first line of evidence, and a next step is to repeat the comparison using climate simulations. Models can generate many more theoretical versions of reality under the same climatic conditions, providing a much larger sample of extreme events. If the models agree with what the observations show, that will strengthen the case that the observed changes represent a genuinely new pattern.

The timing of extreme heat matters for reasons that are both physiological and practical. Heat is harder on the human body when it arrives before people have acclimated to the season, or after they have already endured months of it. It is also harder for communities to prepare for, because cooling centers, heat alerts and public health campaigns are built around a summer calendar. A city that expects its heat season to end in September may find itself unprepared for a deadly hot spell in October. The data from Phoenix, Arizona, illustrate the phenomenon vividly. The city recorded 183 extreme heat days by temperature in the baseline decade of the 1980s, and 338 in the decade ending in 2024. None of the 1980s events fell after the heat season had ended, yet between 2015 and 2024, 6 percent did. The median date of the city’s dry heat extremes moved ten days later in the year, while its humid heat extremes moved 5.5 days earlier.

Phoenix’s recent experience underscores the stakes. After 113 consecutive days above 100 degrees Fahrenheit in 2024, stretching from late September into mid-October, the city went on to tie or break daily temperature records 21 days in a row. Maricopa County, where Phoenix is located, recorded 608 heat-related deaths in 2024, with 46 percent of them in July, the hottest month of the year. In 2023, July accounted for 64 percent of that year’s 645 deaths. And in March of this year, after the study period had ended, the city recorded nine days that topped 100 degrees Fahrenheit—something that had happened only once before in March over the entire historical record. The message is unambiguous: the shoulder seasons, once safe from dangerous heat, are no longer off-limits.

One of the most important questions the researchers addressed is what is driving the pattern. When they tested whether ordinary warming alone could reproduce it, rising average temperatures accounted for changes in the heart of the heat season but not for the lopsided expansion at its edges. Regional factors such as shifting rainfall patterns or changing land use are likely also at work. “We can’t confirm what share of the signal is due to climate change using observations alone,” Ivanovich says, but “it’s certainly the primary component of the story.” Climate models should help determine the respective contributions of human-induced climate change and natural variability, untangling how much of the asymmetry reflects a warming world and how much reflects local dynamics like soil moisture, irrigation and vegetation change.

The implications extend well beyond the heat season itself. Changes in the seasonal timing of extreme heat make it more likely that hot days will intersect with other seasonal hazards: peak wildfire season in the western United States, or peak hurricane season in the Southeast. When multiple hazards coincide or arrive in rapid succession, “they are much more dangerous and impactful than if these events happened in isolation,” Ivanovich says. A wildfire season that overlaps with an extended heat season strains emergency services, power grids and human health simultaneously. The study suggests that cities and public health agencies may need to rethink the entire architecture of heat preparedness, moving away from a summer-only framework toward one that treats dangerous heat as a year-round possibility in half the world’s land area. For the billions of people who live there, the hottest days of the year are no longer where the calendar says they should be.

News Publication Date: 10-Sep-2026

Web References: Not provided

References: Ivanovich, C., Cook, B., & McDermid, S. S. Dangerous Hot Days Are Spreading Beyond Summer. AGU Advances. https://www.eurekalert.org