Report•August 2, 2023

Worldwide daily fingerprints of climate change during Earth’s hottest month

Analysis using the Climate Shift Index (CSI), Climate Central’s daily temperature attribution tool, indicates that human-caused climate change made unusually hot July 2023 temperatures far more likely across the globe. This analysis included 200 countries and 4,700 cities.

Over 6.5 billion people—81% of the global population—experienced at least one day in July with a CSI level 3 or higher. A CSI level 3 indicates that human-caused climate change made those temperatures at least three times more likely.

At least 2 billion people felt a very strong influence of climate change (CSI level 3 or higher) on each of the 31 days in July. Global exposure peaked on July 10, 2023, when 3.5 billion people worldwide experienced extreme heat at CSI level 3 or higher.Well-documented July heat events include those in Mexico, the southern United States, and southern Europe. This global analysis also identifies other regions that experienced extreme July heat altered by climate change—including Florida and the Caribbean, Central America, northern Africa, the Middle East, and parts of South and Southeast Asia.

People living near the equator and on small islands experienced an exceptionally strong influence of human-caused climate change on July temperatures. In tropical climates, relatively small daily temperature anomalies can have a strong CSI signal.

Small island developing states—including 11 in the Caribbean—account for 16 of the 28 countries with the highest July average CSI level (5.0), indicating conditions made at least five times more likely due to human-caused climate change.

Some 870 cities had at least 25 July days at CSI level 3 or higher, including Alexandria, Egypt; Algiers, Algeria; Dhaka, Bangladesh; Douala, Cameroon; Guatemala City, Guatemala; Guayaquil, Ecuador; Havana, Cuba; Jeddah, Saudi Arabia; Mexico City, Mexico; Sanaa, Yemen; Santo Domingo, Dominican Republic; Tampa, United States; and Timbío, Colombia.

Thousands of people die from heat-related causes each year. Attribution science identifies conditions that are becoming more common due to human-caused climate change—and therefore require adaptation efforts such as heat action plans to reduce risk. Heat events with CSI levels 1 through 5 will continue to become more frequent and intense as long as humans continue to burn coal, oil, and natural gas.