Monthly Attribution Overview - April 2025

An analysis of how climate change boosted United States temperatures in April 2025

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 April in cities across the United States. (Dataset downloadable as Excel workbook here.)

1. High Level Findings

• April temperature anomalies in the U.S. were elevated across the board: 182 out of 191 analyzed cities were warmer than normal. The highest anomalies stretched from Texas, the Carolinas, and throughout the Southeast (Figure 1).

• The average temperature anomaly across all cities was 2.1°F. For 24% of stations (46 cities), this ranked amongst the top 10 warmest April monthly temperatures on record (average stations have data reaching back to 1893).

• Climate Shift Index values stood out in the Southeast. This region experienced the most days at or above a CSI of 2, indicating that temperatures on these days were made at least twice as likely to occur as a result of climate change. 25 cities across the country experienced at least a week of days at or above a CSI of 2.

• Long-term warming trends during April (see our 2024 Spring Package) show that nearly all cities in this analysis have gotten warmer since 1970.

Figure 1. Threaded ACIS temperature anomalies for April 2025 relative to the 1991-2020 standard normal period. Analysis based on ACIS data.

Figure 2. Days with a CSI of 2 or higher for April 2025 for ACIS threaded stations. Analysis based on ERA5 data.

2. Local Temperature Anomaly Analysis

• Shreveport, Louisiana, was the most unusually hot city in April, with temperatures 6.33°F hotter than normal. This was also its hottest April on record.

• North Carolina stood out overall: three of its five cities — Raleigh, Charlotte, and Asheville — had their hottest April on record, while Greensboro and Wilmington had their second and fifth hottest April, respectively. 

• Eight cities had temperature anomalies greater than or equal to 5°F, all in the South and Southeast

• The average temperature anomaly across all cities analyzed was 2.1°F.

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

• Reno, Nevada, warmed the most out of all the analyzed cities. The average April in Reno is 8.0°F warmer than it was in 1970.

Table 1. Top 10 ACIS stations with the highest April 2025 temperature anomaly.

Table 2. Top 10 ACIS stations with the fastest warming April since 1970.

3. Local Climate Shift Index Analysis

• Honolulu, Hawaii had 23 days at CSI 5, indicating that temperatures on those days were made at least 5 times more likely because of climate change.

• 25 cities across the country experienced at least a week of days at or above a CSI of 2.

• On average, cities in the Southeast experienced the highest number of days (6.2) with a CSI of 2 or above.

• Even though San Juan had a negative temperature anomaly—meaning it was cooler than the 1991–2020 average—it still experienced one of the highest numbers of days with a Climate Shift Index (CSI) of 2 or higher. This is because temperature anomalies are measured relative to recent climate norms (1991–2020), while the CSI reflects how much warmer conditions are compared to pre-industrial times. So, while San Juan may have felt cooler relative to recent decades, it was still significantly warmer than a typical pre-industrial April.

Table 3. Top 10 ACIS stations with the highest number of days at or above a CSI of 3 during April 2025.

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. 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.