Study Predicts Additional Month of 100-Degree Days at US Military Bases by Midcentury

WASHINGTON - Over the next three decades U.S. military bases in the contiguous United States could average an extra month of dangerously hot days each year when the heat index—or “feels like” temperature—exceeds 100 degrees Fahrenheit, according to an analysis released today by the Union of Concerned Scientists (UCS).

Building on data from UCS’ “Killer Heat” study published in July, this new analysis calculated the increase in dangerously hot days that the 169 major military installations in the contiguous U.S. would experience by midcentury if no action is taken to reduce carbon emissions. Under this scenario, carbon emissions would continue to rise and the global average temperature would increase about 8 degrees Fahrenheit (4.3 degrees Celsius) above pre-industrial levels by century’s end. The study defined major military bases as ones that have at least 1,000 servicemembers on site.

“The three hottest bases by midcentury—Marine Corps Air Station in Yuma, Arizona; MacDill Air Force Base in Florida; and Homestead Air Reserve Base in Florida—would each experience the equivalent of nearly four months per year with a heat index over 100 degrees Fahrenheit,” said Kristy Dahl, a senior climate scientist at UCS and the lead author of the study. “The growing number of dangerously hot days could pose a challenge to the military’s efforts to protect service members’ health while also ensuring mission readiness.”

Last year alone, nearly 2,800 members of the U.S. Armed Services suffered heat-related illnesses or injuries. The rate of these incidents is rising in every branch of the military and is now roughly 50 percent higher than it was five years ago.

More than 90 percent of heat-related illnesses experienced by U.S. servicemembers occur in the United States, according to Pentagon data. The largest number of incidents from 2014 through 2018 occurred at Fort Benning, an Army basic training facility in Georgia. Fort Benning currently experiences an average of 16 days per year with the heat index above 100 degrees Fahrenheit. The study shows that the number of such extreme-heat days would more than quadruple to 73 per year by midcentury if we do not take rapid action to reduce carbon emissions.

The other bases with the highest numbers of heat-related illnesses—Fort Bragg, an Army base in North Carolina; Marine Corp Base Camp Lejeune in North Carolina; and Fort Campbell, an Army base in Kentucky—now each experience roughly a week and a half per year with a heat index exceeding 100 degrees Fahrenheit; these bases are projected to experience two months per year of such conditions by midcentury. At Fort Polk, an Army base in Louisiana, the U.S. base with the fifth highest number of heat-related illnesses, the number of days with a heat index above 100 degrees Fahrenheit would more than triple—from nearly a month’s worth of these lethal conditions each year to approximately three months.

Largest Impact on Basic Training for New Recruits

The rising number of days with extreme heat will likely hit new recruits especially hard. Recruits already experience heat-related illnesses at a rate six times higher than that of other enlisted personnel. According to a recent Armed Forces Health Surveillance Branch paper, “Although numerous effective countermeasures are available, heat-related illness remains a significant threat to the health and operational effectiveness of military members and their units and accounts for considerable morbidity, particularly during recruit training in the U.S. military.” 

In addition, statistics show that military servicemembers who are young, non-Hispanic Black, or of Asian/Pacific Island descent, also experience above-average incidences of heat-related illnesses.  

Looking specifically at basic training facilities across the United States, the number of days per year with a heat index above 100 degrees Fahrenheit is projected to quadruple, resulting in an average of 52 days per year by midcentury if carbon emissions are not reduced, according to the UCS analysis. For example:

• Lackland Air Force Base, Texas, is expected to see 105 days per year with a heat index over 100 degrees Fahrenheit by midcentury (an increase of 69 days);
• Marine Corps Recruit Depot Parris Island, South Carolina, is expected to see 73 days per year with a heat index over 100 degrees Fahrenheit by midcentury (an increase of 61 days);
• Fort Benning, Georgia, which reported the most heat illnesses from 2014 through 2018, would experience 73 days with a heat index over 100 degrees Fahrenheit by midcentury (an increase of 57 days).
• Fort Sill, Oklahoma, also is expected to see 73 days per year with a heat index over 100 degrees Fahrenheit by midcentury (an increase of 53 days).

“We are looking at a steep increase in the number of dangerously hot days at basic training camps where new recruits, who are the most susceptible to heat-related illnesses, go through grueling outdoor training,” said Shana Udvardy, climate resilience analyst at UCS and co-author of the study. “Many of these bases are located in hot and humid regions of the United States. Last year, drills had to be rescheduled because of dangerous heat conditions. But how do you reschedule around the entire summer in the decades ahead?”

The analysis also ranked the military bases that are expected to experience the largest increase in the number of days with a heat index over 100 degrees Fahrenheit by midcentury. The top five, listed in order:

• Homestead Air Reserve Base, Florida, (102 more extreme-heat days);
• MacDill Air Force Base, Florida, (96 more extreme-heat days);
• Naval Air Station Pensacola, Corry Station, Florida, (78 more extreme-heat days);
• Naval Air Station Pensacola, Outlying Field Bronson, Florida, (77 more extreme-heat days);
• Naval Air Station Joint Reserve Base New Orleans, Louisiana, (74 more extreme heat days).

“The military has guidelines in place for preventing heat-related illness, but it’s still seeing an increase in servicemembers getting sick,” said Udvardy. “These guidelines may need to be updated to reflect growing risks and must be diligently enforced especially during extreme heat days. Adjustments may have to be made in the times of day or year when it’s safe for soldiers to train outdoors. The best thing we can do to keep our troops—and by extension the country—safe from these worsening conditions is to enact policies that encourage a rapid transition to a clean energy economy. At the same time, we should be working with the rest of the world through the Paris climate agreement to rapidly and dramatically reduce carbon emissions. That would significantly limit the increase in dangerously hot days ahead and protect our most vulnerable communities.”