Much of the western United States is experiencing record temperatures — reaching the sorts of highs in October that are normally associated with some of the hottest days of summer.
Palm Springs, California, hit a staggering 117 degrees Tuesday, setting a new October record for itself, and matching the highest temperature that’s ever been documented in the US in October.
Other places in California, Arizona, and Wyoming have also experienced some of their hottest October temperatures ever, with San Jose reaching a temperature of 106 degrees, Phoenix hitting 113, and Cheyenne reaching 85 degrees.
All this is part of a larger trend, one with serious consequences: Heat can, in and of itself, be dangerous, especially to the elderly, the very young, and those with chronic health concerns. But it can also have cascading effects, from increasing wildfire risk to disrupting harvests. And, because of the effects of climate change, temperatures like those seen across the western US this week could become far more common.
“Human-caused climate change … is loading the weather dice toward more frequent and intense heat waves,” University of Pennsylvania climate scientist Michael Mann told Vox.
This October heat is largely the result of a phenomenon currently happening in the West known as a “heat dome” — which involves a high-pressure system trapping heat closer to the Earth’s surface.
Long-term climate change, however, is likely exacerbating the heat dome’s effects. Greenhouse gasses that fuel climate change also trap heat, leading to higher temperatures that can make an already hot heat dome even hotter.
According to a study from the climate nonprofit Climate Central, 91 million people in the US experienced 30 or more “risky heat days” this summer, and those were made twice as likely because of climate change. The organization describes “risky heat” days as ones warmer than “90 percent of temperatures observed in a local area over the 1991-2020 period.”
Climate change has also led to higher temperatures around the world throughout this past year, including a particularly hot summer in states across the US. According to the National Oceanic and Atmospheric Administration (NOAA), this was the country’s fourth-hottest summer on record, when looking at temperatures from June through August 2024. During those months, the average temperature in the contiguous United States was 73.8 degrees Fahrenheit — 2.5 degrees above the average from 1991-2020.
That was noticeable in multiple places, including Phoenix, which experienced more than 100 consecutive days of 100-degree heat or higher this year. Globally, the world could also be on track to hit its hottest year on record.
In addition to getting warmer, summers are getting longer, with Drexel University researchers noting that seasonal temperatures are lasting 30 days longer than they have in the past, meaning well into October for some in the northern hemisphere.
That means fall doesn’t bring the same relief from heat it once did. As a September Climate Central report, which looked at 242 US cities, found, fall temperatures went up 2.5 degrees, on average, between 1970 and 2023.
The warmer fall days could have major implications for natural disasters, especially for wildfires in places like Southern California, where heat amplifies the risk of potential blazes on drier landscapes that have also seen decades of fire suppression. While wildfire season has typically run from early summer into the fall, it has the potential to go longer as higher temperatures persist.
More days with higher temperatures can also translate to increased cases of heat stroke, cardiovascular problems caused by stress on the heart, and respiratory challenges. They can extend, too, the window when people experience seasonal allergies.
Additionally, warmer falls could affect plant and animal preparations for hibernation, severely shortening the time they usually take to prepare for winter, and delaying processes like changes in foliage and leaf dropping. Farmers may increasingly need to shift planting and harvesting schedules for different crops as temperatures continue to fluctuate as well.
Short of major changes needed to curb human contributions to global warming, this year’s October heat waves aren’t likely to be a fluke. As Mann told Vox, “The warming will continue until we bring carbon emissions to zero.”
