Arizona is measurably and consistently getting hotter. State temperature records, broader Northern Hemisphere reconstructions, and the lived experience of anyone who has spent a few summers in Phoenix all point in the same direction. The warming is not a single-cause story, though: global greenhouse gas emissions set the baseline trend, recurring atmospheric patterns called heat domes concentrate extreme heat over the interior West, and the rapid urbanization of the Phoenix metropolitan area adds a layer of localized warming on top of everything else. Understanding which of these drivers matters most depends on whether you are asking about the state as a whole or about a specific neighborhood in Maricopa County.
What the Temperature Record Actually Shows
Arizona’s average annual temperature has climbed roughly two to three degrees Fahrenheit since the early twentieth century, with most of that increase packed into the last few decades. Nighttime low temperatures have risen even faster than daytime highs in the state’s urban corridors, which means the relief that used to come after sunset is shrinking. Phoenix Sky Harbor International Airport, where one of the longest continuous weather records in the state is maintained, has logged a rising number of days above 110 °F per year since the 1990s.
This local warming sits within a hemisphere-wide trend. A recent study using nearly two thousand years of tree-ring data found that the summer of 2024 was the warmest in the entire instrumental record, about 2.8 °C above the preindustrial baseline. The full range of natural climate variability over the past two millennia spanned roughly 4 °C; twenty-first-century warming has stretched that range to about 5.5 °C.1Discover Geoscience. 21st century Northern Hemisphere warming in a 2025-year context of climatic events using tree-ring data In other words, the warming Arizona is experiencing is not a local curiosity. It is part of a planetary shift that has pushed summer temperatures well beyond anything that occurred naturally over the past two thousand years.
Why Heat Domes Keep Parking Over Arizona
If global warming sets the thermostat higher, heat domes are the mechanism that cranks it to extreme levels on particular days and weeks. A heat dome forms when a strong, persistent ridge of high pressure traps hot air near the surface and prevents it from rising and dissipating. The interior western United States and northern Mexico sit in the zone of highest heat-dome frequency across the entire North American continent. A climatological analysis spanning 1940 to 2025 found that nearly all of the extreme heat events identified in that region were directly part of a heat dome structure.2Weather and Climate Extremes. A climatology of heat domes over North America – Section: 4.3. Heat dome climatology
Arizona’s geography makes it especially vulnerable. The state’s low elevation deserts sit in a broad basin flanked by mountain ranges, and that topography can reinforce the subsiding, compressing air that defines a heat dome. When one of these events stalls over the region for several days, temperatures do not just spike during the afternoon; they stay dangerously elevated around the clock. The combination of global background warming and these recurring atmospheric patterns means that Arizona’s worst heat events are both hotter and longer than they used to be.
The Urban Heat Island Layer
Phoenix is the hottest large metro in the United States, and a meaningful fraction of that distinction comes not from its latitude or its desert climate but from the way the city itself is built. Roads, rooftops, parking lots, and building walls absorb solar energy during the day and radiate it back as heat well into the night. In a sprawling metro area that has grown from about one million people in the 1960s to nearly five million today, the sheer surface area of heat-absorbing material is enormous.
The difference between downtown Phoenix and the surrounding undeveloped desert can reach several degrees Fahrenheit on a calm summer night. That gap, often called the urban heat island effect, matters most after dark because it prevents the human body from recovering during the hours that should be coolest. It is also unevenly distributed: neighborhoods with less tree canopy, more asphalt, and older housing stock tend to run hotter than wealthier areas with mature landscaping and lighter-colored building materials. Research across thousands of U.S. communities has documented a clear link between neighborhood income, tree cover, and local temperatures, and Phoenix is one of the starkest examples of that pattern.3PubMed Central. The tree cover and temperature disparity in US urbanized areas: Quantifying the association with income across 5,723 communities
This means that when people ask “is Arizona getting hotter,” the answer depends partly on where in Arizona you stand. A resident of a well-shaded Scottsdale subdivision and a resident of a treeless corridor in south Phoenix are technically in the same metro area, but they may experience meaningfully different temperatures on the same summer night.
The Human Cost of Rising Heat
Heat is already the deadliest weather-related hazard in the United States, and Arizona, particularly Maricopa County, has become the epicenter of that crisis. Maricopa County has tracked heat-associated deaths through a dedicated surveillance program since 2006. Over that period, the number of deaths each year has risen steadily, with 2022 showing a 25 percent increase over 2021 alone.4Disaster Medicine and Public Health Preparedness. Heat-Associated Death Surveillance in Maricopa County During the 2023 Heat Wave The 2023 season was even worse, making national headlines as morgues strained under the volume of cases.
The victims are disproportionately people experiencing homelessness, older adults living alone, and outdoor workers. Many heat-associated deaths occur indoors, in homes where air conditioning has broken down or been shut off because the electricity bill is unaffordable. When nighttime temperatures stay above 90 °F, the body cannot cool itself through normal thermoregulation during sleep, and the cumulative heat load builds over successive days. That is why a four-day heat wave can be far more dangerous than a single record-setting afternoon.
Outdoor Work in Extreme Heat
Arizona’s construction, agriculture, and landscaping industries expose hundreds of thousands of workers to conditions that are measurably harder on the body than they were a generation ago. A comprehensive review and meta-analysis pooling data from dozens of field studies across multiple countries found that occupational heat stress raises core body temperature and heart rate while drastically reducing the capacity for manual labor. The effect on physical work output was large: heat stress accounted for more than two-thirds of the reduction in metabolic rate observed among outdoor workers.5PubMed Central. Occupational heat strain in outdoor workers: A comprehensive review and meta-analysis
For Arizona specifically, the practical implication is that the outdoor work season is shrinking from both ends. Mornings that used to be cool enough for heavy labor now start hot, and the midday hours when work must stop are stretching longer. Some construction firms in the Phoenix area have shifted to overnight schedules during June, July, and August, pouring concrete and laying block under floodlights to avoid peak daytime temperatures. That adaptation carries its own costs: lighting, supervision, and worker fatigue all add expense and complexity. The economic productivity loss from extreme heat in the state is real and growing, even if it does not show up in a single dramatic event the way a hurricane or flood does.
What Cities Are Doing About It
Local governments in Arizona have begun experimenting with ways to lower temperatures at the neighborhood level. The most studied approach in the Phoenix area involves replacing dark, heat-absorbing surfaces with more reflective alternatives. A modeling study of suburban Phoenix found that switching to reflective concrete pavements dropped local air temperatures by about 0.2 to 0.4 °C, while reflective roofs and walls produced a somewhat larger reduction of 0.4 to 0.7 °C. Replacing all roofs, walls, and pavements with reflective coatings in a given area yielded a decrease of roughly 0.8 to 1.0 °C.6Sustainability. Cool Pavement Strategies for Urban Heat Island Mitigation in Suburban Phoenix, Arizona
A one-degree drop might sound modest, but in a city where the difference between survivable and deadly conditions can hinge on a few degrees during overnight hours, those numbers add up. Phoenix has also invested in tree-planting programs, shade structures at bus stops, and cooling centers where residents can escape the heat during the worst afternoons. Tempe, Mesa, and other surrounding cities have tested cool-pavement coatings on public roads.
The honest assessment, though, is that these interventions are fighting the margins. They can reduce the urban heat island premium and protect the most vulnerable residents, but they do not touch the baseline warming driven by greenhouse gas concentrations in the atmosphere. Even if Phoenix became the most reflective, best-shaded city in the desert, its temperatures would still be rising along with the rest of the planet. Mitigation at the city level and mitigation at the global-emissions level operate on completely different scales, and Arizona needs both.
Why Nighttime Warming Matters More Than You Think
Most media coverage of Arizona heat focuses on daytime record highs, which are dramatic and easy to visualize. But researchers who study heat mortality increasingly emphasize that overnight low temperatures are a better predictor of danger. The human body relies on cooler nighttime hours to recover from the physiological strain of daytime heat. When the overnight low stays above 90 °F, that recovery window closes, and the cumulative stress on the cardiovascular system ramps up with each passing night.
Nighttime lows in Phoenix have risen faster than daytime highs over the past several decades, driven largely by the urban heat island effect. Concrete and asphalt release stored heat slowly after sunset, keeping the air warm through the night. In undeveloped desert just outside the metro boundary, nighttime temperatures can be ten or more degrees cooler. That gap has widened as the city has expanded outward, paving over more of the surrounding landscape. For the millions of people living in the metro area, the practical experience of summer in Phoenix is shaped less by the afternoon peak and more by whether they can cool down at night.
Water, Drought, and the Feedback Loop
Arizona’s warming trend does not exist in isolation from its water crisis. Higher temperatures increase evaporation from reservoirs and soils, reduce snowpack in the mountains that feed the Colorado River system, and raise the water demand from agriculture and residential landscaping simultaneously. The relationship runs in both directions: as drought strips moisture from the soil and reduces vegetation cover, the land absorbs and re-emits more heat, creating a feedback loop that amplifies warming in already-dry landscapes.
Lake Mead and Lake Powell, the two largest reservoirs in the Colorado River system, have dropped to historically low levels over the past two decades. Some of that decline reflects overallocation of water rights that dates back a century, but rising temperatures have meaningfully worsened the deficit by increasing evaporative losses. For Arizona residents, this means that the heat question and the water question are really the same question viewed from different angles. A hotter Arizona is a drier Arizona, and a drier Arizona is, in turn, a slightly hotter one.
How the Southwest Compares
Arizona is not the only state in the region experiencing rapid warming. Nevada, Utah, New Mexico, and parts of Southern California have all seen comparable temperature increases since the mid-twentieth century. The interior West as a whole warms faster than the national average because it lacks the moderating influence of large water bodies and because its arid landscapes absorb and radiate heat efficiently. The same heat-dome patterns that affect Arizona extend across much of this region.
Where Arizona stands out is in the combination of extreme heat and rapid population growth. Phoenix has been one of the fastest-growing metros in the country for most of the past three decades, which means more people are moving into harm’s way at the same time that conditions are worsening. Many new arrivals come from cooler climates and may underestimate the danger of a 115 °F afternoon or the importance of staying hydrated during a hike in the Superstition Mountains. Emergency rooms in the metro area see a spike in heat-related illness every year that correlates not just with temperature but with the number of people who are new to the desert and unfamiliar with its risks.
Misconceptions That Get People Into Trouble
One of the most persistent myths about Arizona heat is that “it’s a dry heat” makes it safe. Low humidity does make high temperatures more tolerable up to a point, because sweat evaporates more efficiently. But that advantage collapses above roughly 115 °F, where the rate of heat gain from the environment overwhelms the body’s evaporative cooling capacity regardless of humidity. At those temperatures, every minute of direct sun exposure adds to a deficit the body cannot easily pay back.
Another common misunderstanding is that air conditioning solves the problem. For people with reliable access to a cooled indoor space, it largely does. But about 10 percent of Maricopa County’s heat-associated deaths occur in homes that had functioning air conditioning, suggesting that other factors such as isolation, chronic illness, or reluctance to run the unit due to cost play a role. And for the roughly 9,000 people experiencing unsheltered homelessness in the Phoenix metro on any given night, air conditioning is not part of the equation at all. The gap between the heat that statistics describe and the heat that vulnerable populations actually endure is one of the most underappreciated aspects of Arizona’s warming trend.
A third misconception is that the warming is cyclical and will reverse on its own. Arizona has always experienced natural temperature variability, including cooler decades. But the tree-ring record spanning two millennia makes clear that the current warming has pushed temperatures beyond the full range of that natural variability.1Discover Geoscience. 21st century Northern Hemisphere warming in a 2025-year context of climatic events using tree-ring data What Arizona is experiencing today is not the hot end of a pendulum swing. It is a new baseline, and the trajectory remains upward.