Climate Shift Index Alert•June 11, 2024
Climate change influencing severe heat in Southwest U.S.
The Southwest United States is poised to experience unusually intense heat over the next several days (June 11-13), with high temperatures made at least 5 times more likely because of human-caused climate change.
Note: This event may continue beyond June 13. Use the Global Climate Shift Index map to stay updated on heat in your region.
How unusual is this heat event?
This week, millions of people across the U.S. Southwest will be exposed to multiple days moderate to major heat, which will significantly affect those without access to effective cooling and/or adequate hydration.
Excessive Heat Warnings and Watches have been issued for parts of Arizona, New Mexico, and Nevada including Phoenix, Tucson, Las Cruces and Las Vegas.
High temperatures of 105°F to 112°F are expected in the lower deserts, and 102°F to 108°F in the higher terrain, through June 13.
Elevated nighttime temperatures in the 73°F to 83°F range are expected across much of this region.
Note: Find information on cooling centers, hydration stations and respite centers in the Phoenix area (Maricopa County) and the Las Vegas area (Clark County).
This is a continuation of an extreme heat event that started last week.
Last week, climate-fueled extreme heat impacted the Southwest with record-setting high temperatures recorded in Phoenix (113°F), Las Vegas (111°F), Reno (98°F), and Flagstaff (91°F) on June 6 (the peak of the heat wave).
Record warm low temperatures were also set in Phoenix (87°F) and Las Vegas (85°F). Unusually high lows contribute to the risk of heat related illness, by not allowing time for our bodies to cool down.
How has climate change influenced this heat?
Daily average temperatures are expected to reach Climate Shift Index (CSI) levels of 5 in central and eastern California, Nevada, New Mexico, Utah, Colorado, and Arizona. A CSI level 5 indicates that human-caused climate change made this excessive heat at least five times more likely, signifying an exceptional climate change event.
Over the next three days, 17 million people in the Southwest will experience at least one day with CSI level 5.
Use the Climate Shift Index global map to see CSI levels in your city and region, and see our FAQs to learn about the CSI in both English and Spanish.
What impacts are we seeing with this continued extreme heat?
11 people were hospitalized due to heat exhaustion at a Trump rally in Phoenix, Arizona. Two dozen others were hospitalized and almost 100 people took refuge in cooling tents to escape the scorching temperatures at a rally later in the week in Las Vegas.
Several wildfires broke out in California last week during the heatwave. In the Central Valley, northeast of Los Angeles, over 3,500 acres of agricultural land were burned.
In Nevada, in a span of less than 36 hours, at least 12 calls were made to the Clark County fire department related to heat exposures with three-quarters of them leading to hospitalization.
Local organizations in Nevada spent several days last week bringing water and other resources to police officers and people experiencing homelessness who were impacted by the excessive heat, along with rides to cooling shelters.
In Henderson, Nevada (~15 miles southwest of Las Vegas), the asphalt reached a temperature of 162°F, highlighting the dangerous burn threat posed to pets and livestock.
What do experts say?
Dr. Andrew Pershing, VP of Science at Climate Central, said:
“The Southwest is the hottest part of the country, and human-caused climate change is making it even hotter. Heat waves like this will continue to become longer, more intense, and more dangerous until carbon pollution ends.”
How do we know climate change is influencing this heat?
The Climate Shift Index uses peer-reviewed methodology to estimate how climate change has increased the likelihood of a particular daily temperature. It can be run using historical or forecast temperatures.
Using computer models, we compared the likelihood that these temperatures would occur in a world without carbon emissions released by humans, versus in today's world with decades of carbon emissions building up in the atmosphere. This is an established scientific method to determine how much climate change has or has not affected individual extreme weather events.
For this analysis, temperatures come from the National Center for Environmental Prediction’s Global Forecast System.
To request an interview with a Climate Central scientist, please contact Peter Girard at pgirard@climatecentral.org
Reporting resources
Until greenhouse gas emissions end, heatwaves everywhere will continue to become hotter and more dangerous. Explore quick facts and local analyses on the links between climate change and extreme heat in:
Climate Central’s Extreme Weather Toolkit: Extreme Heat
World Weather Attribution’s guide to reporting on extreme heat and climate change
Yale Climate Connections’ summary of the connection between heat waves and climate change.