July 19, 2025 - By to Oceans Influence on Climate & Weather, Physical Oceanography - Extreme heat is the leading weather-related cause of death in the United States. In a new study published in Nature Communications, scientists found a link between the long-lasting 2023 heatwave over the southwest US and Mexico and the record warm sea surface temperatures in both the Atlantic and Pacific Ocean.
In 2023, a severe heat wave event occurred over the southwestern United States and Mexico, which lasted from mid-June to early August, affecting over 100 million people, and was responsible for over 300 deaths. The compounded effect of extreme heat and drought was responsible for $14.5 billion in economic loss, making this event the costliest North American weather and climate disaster of 2023. This event featured extreme temperatures, with Phoenix, Arizona experiencing both the longest continuous stretch of daily maximum temperature exceeding 104°F (55 days) and the warmest nighttime minimum temperature on record (97°F). This heat wave was far reaching, setting new all-time record temperatures throughout the southern US in places like New Orleans, Louisiana and the Caribbean.
In this study, scientists at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) and the University of Miami Cooperative Institute for Marine and Atmospheric Studies (CIMAS) show a physical link between the long duration extreme heat over the southwest US and Mexico and the record warm North Atlantic sea surface temperatures and a growing El Niño in the Pacific.
El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO) cycle, a recurring climate pattern that occurs on average from 2 to 7 years, which involves changes in the sea surface temperature in the central and eastern Pacific Ocean.
Through observations and model simulations, scientists show that the extremely warm sea surface temperatures in the Atlantic and Pacific oceans were responsible for the persistence of the heat wave in the region. The warm sea surface temperatures impacted large-scale wind patterns which created a high-pressure system that persisted for more than six weeks, greatly increasing land surface temperatures, reducing precipitation, and causing the heat wave to grow and last.
The high tropical Atlantic sea surface temperature was found to be the dominant factor, which increased the likelihood of heat waves over the region. Meanwhile, the influence of El Niño was much smaller. However, the combination of a warm Atlantic and a warm Pacific significantly amplified regional heat waves, doubling their number, tripling their days, and increasing their duration by about 50%.
“This 2023 heat wave lasted twice as long as usual, putting a real strain on human health and essential services/infrastructure,”said Hosmay Lopez, AOML oceanographer and lead author of the study. “The main culprit? Record-warm Atlantic Ocean temperatures. A developing El Niño in the Pacific also played a smaller role.”
“Our study reveals that closely watching how the ocean and atmosphere interact is vital, “Lopez added. “These interactions are crucial for making better long-range forecasts of extreme weather.”
According to the World Meteorological Organization, 2023 was ranked as the second warmest year in the global surface temperature record since 1850 (only surpassed by 2024), setting warm surface temperature records over more than 20% of the global land surface.
Heat waves can significantly impact human health, the environment and the economy in sectors like healthcare, agriculture, energy and much more. Improving the knowledge of these events can greatly benefit these industries. Improving heatwave predictions and future projections hinges on understanding both shorter-term weather and climate variability, and longer-term drivers of heatwave patterns. The aim is to enhance predictions beyond the typical weather forecast range, the research authors said.
Source: NOAA
