It reached 110 degrees in these US cities. In October.

Much of the western U.S. is experiencing record-breaking temperatures, reaching highs in October that are typically associated with some of the hottest days of summer.

Palm Springs, California, reached an incredible 117 degrees on Tuesday, setting a new October record and reaching the highest temperature ever documented in the United States in October.

Other locations in California, Arizona and Wyoming also experienced some of the hottest October temperatures ever: San Jose hit 106 degrees, Phoenix hit 113 and Cheyenne hit 85 degrees.

This is all part of a larger trend with serious consequences: Heat can be dangerous in and of itself, especially for the elderly, the very young, and those with chronic health problems. But it can also have cascading effects, from increasing the risk of forest fires to crop failures. And due to the effects of climate change, temperatures like those seen in the western United States this week could become far more common.

“Human-caused climate change … is pushing the weather 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 occurring in the West known as a “heat dome.” This is a high-pressure system that traps heat closer to the Earth's surface.

However, long-term climate change is likely to increase the effects of the heat dome. Greenhouse gases that drive climate change also trap heat, leading to higher temperatures that can make an already hot heat dome even hotter.

According to a study by climate nonprofit Climate Central, 91 million people in the U.S. experienced 30 or more “high-risk hot days” this summer, and they were twice as likely due to climate change. The organization describes “high-risk hot days” as those that are warmer than “90 percent of the temperatures observed in a local area during 1991-2020.”

Climate change has also led to higher temperatures around the world last year, including a particularly hot summer in states across the United States. 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 to August 2024. During these months, the average temperature in the contiguous United States was 73.8 degrees Fahrenheit – 2.5 degrees above the 1991-2020 average.

That was noticeable in several places, including Phoenix, which saw temperatures of 100 degrees or more on more than 100 consecutive days this year. Globally, the world could also be on track to experience the warmest year on record.

Summers are not only getting warmer, but also longer. Drexel University researchers found that seasonal temperatures are lasting 30 days longer than in the past, meaning well into October for some in the Northern Hemisphere.

This means that fall no longer brings the same relief from the heat that it once did. A September Climate Central report that examined 242 U.S. cities found that fall temperatures rose an average of 2.5 degrees between 1970 and 2023.

The warmer fall days could have a significant impact on natural disasters, particularly wildfires in places like Southern California, where the heat increases the risk of potential fires in drier landscapes that have also seen decades of fire suppression. While wildfire season typically lasts from early summer through fall, there is a chance it could last longer if temperatures persist.

More days with higher temperatures can also lead to more frequent cases of heat stroke, cardiovascular problems due to strain on the heart, and difficulty breathing. They can also extend the window in which people suffer from seasonal allergies.

In addition, warmer falls could affect plants and animals' preparations for hibernation, significantly shortening the time they normally need to prepare for winter and delaying processes such as leaf change and leaf drop. Farmers may increasingly need to postpone planting and harvesting schedules for various crops as temperatures also continue to fluctuate.

Unless major changes are needed to curb human contributions to global warming, this year's October heatwaves are unlikely to be a coincidence. As Mann told Vox: “The warming will continue until we get CO2 emissions to zero.”