During the Cold War, American activities caused radioactive contamination in three countries, and the U.S. Government Accountability Office (GAO) recently issued a report about the status of these sites.

In the Republic of the Marshall Islands (RMI), the U.S. conducted 67 nuclear tests at the Bikini Atoll and Enewetak Atoll between 1946 and 1958. Rising sea levels caused by climate change could mobilize the radioactive contamination, posing risks to fresh water and food sources. According to the GAO, RMI officials (and residents) believe the U.S. Department of Energy is downplaying the current risk to human health posed by climate change-induced disturbances. Improvements in communication and environmental remediation strategies are recommended.

In Greenland (part of the Kingdom of Denmark), the contamination stems from a closed nuclear reactor that powered a U.S. military research base. Radioactive liquid is frozen in ice sheets, which Denmark is monitoring, as there is concern that climate change could release the contamination. While some studies suggest that much of the waste has decayed and will be diluted by melting ice, others highlight the presence of chemical waste such as polychlorinated biphenyls that could pose health risks.

In Spain, two U.S. defense aircraft collided in 1966, spreading radioactive debris on the town of Palomares. The countries worked together to remediate the area after the accident, but some radioactive contamination remains. Both countries signed a 2015 statement of intent to further clean up the site, but they still have not reached a final agreement.