U.S. Temperature Attribution Overview: October 2024

Analysis: How climate change boosted United States temperatures in October 2024

Using Climate Central’s Climate Shift Index (CSI) tool to measure the impact of climate change on daily temperatures across the United States, as well as NOAA’s Applied Climate Information System (ACIS) to find daily temperature information, we have compiled a high-level overview of how climate change has affected temperature trends in October in cities across the United States. Download full report (PDF)

1. High level findings (download local data, including monthly precipitation)

• October temperature anomalies in the U.S. were elevated across much of the country: 185 out of 191 analyzed cities were warmer than normal. The highest anomalies stretched from the Rocky Mountains to the Mississippi (Figure 1).

• This was the hottest October on record in 19 cities – including 9 cities in Texas– and was in the top 5 hottest Octobers for an additional 19 cities.

• The Southwest showed particularly elevated October temperatures. Average temperatures across 8 cities in New Mexico, Colorado, Arizona, and Utah were 7.1°F higher than normal.

• Climate Shift Index (CSI) values meanwhile followed a different trend: California, Arizona, New Mexico, Texas, and Florida stood out as the states with cities experiencing the highest number of days with climate change-influenced temperatures at or above CSI 3 (temperatures made at least 3x more likely because of climate change) (Figure 2).

• On average, cities analyzed in the Southwest experienced at least 7 days with temperatures resulting in CSI values greater than or equal to 3.

Figure 1. Threaded ACIS temperature anomalies for October 2024  relative to the 1991-2020 standard normal period. Analysis based on ACIS data.

Figure 2. Days with a CSI of 3 or higher for October 2024 for ACIS threaded stations. Analysis based on ERA5 data (October 1-29) and GFS data (October 30-31).

2. Local temperature anomaly analysis (download local data, including monthly precipitation)

• The most unusually hot city in October was Grand Junction, Colorado, where it was 8. 9°F hotter than normal.

• 56 cities had October temperature anomalies greater than 5°F. These included 11 in Texas and 5 in Iowa.

• The average temperature anomaly across all cities was 3.6°F.

• 185 out of 191 ACIS stations analyzed had positive temperature trends for October, indicating that these cities have been warming on average since 1970.

• Reno, NV had an unusually warm October (with an average daily temperature anomaly of 3.0 °F), and is the fastest-warming ACIS station for October on average, warming 7.4 °F on average since 1970.

3. Local Climate Shift Index analysis (download local data, including monthly precipitation)

• 12 out of 191 ACIS stations analyzed had at least one week with daily CSI values greater than or equal to 3, indicating that temperatures on those days were made at least three times as likely due to climate change in those cities.

• San Juan, Puerto Rico had 16 days at CSI 5, indicating that temperatures on these days were made at least 5 times more likely to occur because of climate change.

• All 3 cities in Arizona were in the top 10 cities with the strongest climate signal. Additionally, each of these cities had at least 9 days of temperatures with CSI values of 5.

• On average, cities analyzed in the Southwest experienced at least 8 days with temperatures resulting in CSI values greater than or equal to 3.

Methods

Calculating the Climate Shift Index

All Climate Shift Index (CSI) levels reported in this brief are based on daily average temperatures and  ERA5 data from October 1 to October 26, 2024, and GFS data from October 27 to October 30, 2024. See the frequently asked questions for details on computing the Climate Shift Index, including a summary of the multi-model approach described in Gilford et al. (2022).

City Analysis

We analyzed 191 Applied Climate Information System (ACIS) stations associated with U.S. cities. For each city, we found the CSI time series from the nearest 0.25° grid cell. We calculated the number of days at CSI levels 2, 3, 4, and 5. We used ACIS data to find the average monthly temperatures, temperature anomalies, and precipitation information, and to derive average monthly warming trends for each city.

Click here for more information about the Climate Shift Index

Major funding provided by the Bezos Earth Fund and The Schmidt Family Foundation.