As sailors from around the world train in Hawaii at the biennial Rim of the Pacific training exercise, climate change is taking center stage for several planners. The impact of climate change has been a topic of discussion in classroom lessons during the international exercise as service members prepare to go out to sea for the world’s largest recurring naval war game.

Among the exercises military forces are conducting in Hawaii is simulated humanitarian disaster response in partnership with officials from the United Nations and U.S. government civilian agencies. Joyce Blanchard, one of the organizers of the training and an adviser at U.S. Indo-Pacific Command’s Center for Excellence in Disaster Management and Humanitarian Assistance, said that this year’s iteration is different.

“We looked at the exercise and then through 2018 to 2020 we ripped the exercise down and completely redesigned it to make it more realistic on how foreign military forces respond today,” Blanchard said. “We included more discussions on climate change and climate security and talking about resilience and planning together to look towards the future and how all the militaries can come together and help that process.”

The military’s concerns about climate change aren’t new. In 2013 Adm. Samuel Locklear, commander of what was then Pacific Command, told The Boston Globe that climate change is the greatest threat to the Pacific region and that resulting conflicts and disasters “will cripple the security environment, probably more likely than the other scenarios we all often talk about.”

Nearly a decade later many of these concerns are no longer hypothetical.

“Especially in the Asia-­Pacific region you have displaced populations, and with the increase in temperatures you have drought,” Blanchard said. “And as countries build more dams and water becomes more scarce, you have a lack of water. In the future, you can have food insecurity, water insecurity, and then that leads to security issues in the future — and of course, war.”

Natural disasters like hurricanes and wildfires have become more frequent as the climate changes. During a symposium on military medicine held Friday, Surgeon General of the Australian Defence Force Rear Adm. Sarah Sharkey told an audience that in addition to more extreme natural disasters, scientists and doctors are looking at how warmer temperatures can affect the spread of disease. Sharkey warned that it could cause previously seasonal illnesses to become year-round problems.

Large-scale natural disasters occasionally prompt military responses. Governments of affected countries often call upon foreign militaries in the immediate aftermath. With their numerous ships, aircraft and logistical support, military forces are able to rapidly deliver aid, conduct search-and-rescue missions and build temporary structures to set the stage for long-term recovery.

But military activity itself can also contribute to climate change. A 2019 report from Brown University found that the U.S. military produces more carbon emissions than many entire industrialized nations. In Hawaii the contamination of the Navy’s Oahu water system by fuel from the massive strategic reserve at the Red Hill fuel storage facility — which sits above a critical aquifer that provides most of Honolulu’s drinking water — has intensified the debate over the U.S. military’s fueling needs.

Meanwhile, China has been rapidly building its navy — which is currently the world’s largest. There is no available data of the Chinese military’s fuel use. The Chinese military also has built artificial islands in disputed regions of the South China Sea in order to stake territorial claims, which scientists warn has the potential to threaten already strained fish and reef ecosystems in the region. The Chinese military has not allowed researchers to survey the areas around these new bases.

At the 2022 East-West Center International Media Conference hosted in Honolulu last week, Hilda Heine, former president of the Marshall Islands, said that while China and the U.S. compete for influence across Pacific islands, islanders are fighting for their lives.

“When the highest point in your country is just 2 meters above sea level, even incremental changes pose an existential threat,” Heine told the audience.