The 2021 Red Hill fuel spill poisoned thousands of residents and contaminated Oahu’s drinking water. The Navy’s lack of transparency exacerbated the harm by delaying a response.

When Vice Adm. John Wade, commander of the U.S. Third Fleet and former commander of the Red Hill Task Force, opened the Rim of the Pacific (RIMPAC) 2024 military exercises this year, he embraced “a sacred responsibility to be good stewards of the environment.”

That environment is affected by greenhouse gas emissions, which raise the temperature of the world’s lands and oceans. The carbon emissions from RIMPAC 2024, and all previous RIMPAC exercises, will stay in the atmosphere for hundreds of years. But the Department of Defense did not estimate RIMPAC emissions for this year’s exercise.

RIMPAC emissions include not only the fossil fuel use from the exercises themselves. The three major planning conferences involved hundreds of military personnel traveling to San Diego over the last 18 months and the travel to Hawaii of more than 40 ships and submarines and 150 aircraft, most of which are not based in Hawaii.

The military has not yet published fuel use for RIMPAC 2024. So one of us asked. In response, RIMPAC Public Affairs office said that, although they could not report the final fuel totals, U.S. forces were provided about 20 million gallons of naval and jet fuel from the Defense Logistics Agency. Adding the emissions produced by the participant naval vessels en route to Hawaii, Lennard de Klerk, a military emissions expert based in Europe at the Initiative on GHG Accounting of War, and Neta Crawford estimate RIMPAC 2024 emissions would be about 300,000 tons of CO2 equivalent. That is larger than the annual emissions of the island nations of Samoa, Tonga and Vanuatu, or the combined emissions of the eight lowest-emitting countries in 2022.

But this estimate is low compared to fuel use in a previous RIMPAC exercise. Using publicly available data from RIMPAC 2016, Crawford and de Klerk estimated that the greenhouse gas emissions of RIMPAC 2024 are about 2.5 million metric tons of CO2, including the travel of ships to the exercises. That is about the same as the annual emissions of Washington, D.C. in 2021 or the combined emissions of the world’s 20 lowest-emitting countries.

Both estimates may be conservative because significant data is not publicly available, including the fuel consumption of aircraft from participating countries. We also do not estimate the emissions of the bases in Hawaii which provide the electricity for ships while they are in port for RIMPAC.

RIMPAC may also inhibit the ability of oceans to store carbon. Sonar can harm whales, which are important to the world’s carbon cycle. Here, again, we need to know more about the effects of RIMPAC and similar military exercises on the marine environment.

But RIMPAC certainly imposes important environmental costs for Hawaii and for the planet as a whole in the long term that may outweigh its short term contributions to national security.

A warming atmosphere and ocean means rising sea levels, more frequent storms, disappearing beaches, damaged coral reefs, and unreliable rainfall. The ferocity of last year’s deadly Lahaina wildfire underscores the urgency and high stakes of the climate crisis.

It is long past due for full transparency on military emissions and for militaries everywhere to reduce their carbon footprint. Hawaii cannot hope to manage and reduce its carbon emissions as long as military emissions remain uncounted.

Kyle Kajihiro is an assistant professor of ethnic studies at the University of Hawaiʻi at Manoa; Neta C. Crawford is Montague Burton Professor of International Relations, University of Oxford and co-founder of the Costs of War Project based at Brown University.