The United States Department of Defense faces a new, insidious enemy—a threat that can destroy key U.S. bases, weaken allies, and strike deep within the homeland .
What Is the Threat?
According to the Department of Defense, climate change is a “threat multiplier” because its effects “will intensify the challenges of global instability, hunger, poverty and conflict” . Rising sea levels and more frequent extreme weather events will have a direct impact on the United States’ strategic and defensive interest, But climate change is also indirectly threatening the United States, and is expected to generate more political instability and mass migrations in decades to come.
Rising Sea Levels. Rising sea levels will increasingly threaten strategic military bases in the United States and throughout the world. NASA estimates that global sea levels rose an average of 6.7 inches (17 centimeters) during the 20th century , and may rise as much as 3 feet or more during the 21st century .
Consequently, as many as 19 key military bases may be jeopardized by rising sea levels . For example, one study estimates that four bases, including NAS Key West, are at risk of losing 75-95% of their land by 2100 (see chart below) . The Department of Defense will need to decide between environmental mitigation, land reclamation or complete relocation strategies for these bases .
Unpredictable, Extreme Weather. Event attribution—especially in the case of climate change—remains a probabilistic science . However, annual reports by the National Oceanic and Atmospheric Administration (NOAA) have repeatedly cited climate change as an influencing factor for extreme weather and climate events .
Extreme weather events can hinder military and intelligence operations. For example, extreme storms may inhibit aerial surveillance or reconnaissance capabilities, or may increasingly divert military resources towards humanitarian assistance following extreme weather occurrences .
Global Instability. Climate change also poses severe indirect threats to the United States. For example, the increasingly impactive effects of climate change—such as water shortages or disruptions or reductions in agricultural production—could cause political instability and mass migrations in developing countries .
“Mankind’s relationship with the natural world is aggravating these problems and is a potential source of crisis,” admits U.S. Central Intelligence Agency Director John O. Brennan, “Extreme weather, along with public policies affecting food and water suppliers, can worsen or create humanitarian crises. Of most immediate concern, sharply reduced crop yields in multiple places simultaneously could trigger a shock in food prices with devastating effect, especially in already fragile regions such as Africa, the Middle East, and South Asia” .
Fighting the “Hot War”
The Department of Defense now recognizes climate change as “a present security threat, not strictly a long-term risk” .
For now, the Department of Defense is responding with dual strategies of Adaptation (planning for climate change effects) and Mitigation (reducing the Department’s contribution to climate change) . The Department of Defense is now using climate change considerations for evaluating and modifying its range of military and supply chain operations, including its training and testing programs and its artificial and natural infrastructures .
Unfortunately, these dual strategies are reactive, and only deal with the symptoms of climate change. Even the three goals outlined in the Department of Defense’s Climate Change Adaptation Roadmap—to identify and assess the effects of climate change, to incorporate climate change considerations across the full range of missions and activities, and to collaborate with internal and external entities to understand, assess and respond to climate change realities—do not address the root of the problem.
In the case of climate change, the Department of Defense should heed the advice of one of their most respected strategists. More than two thousand years ago, Sun Tzu advised that “[s]ecurity against defeat implies defensive tactics,” but the “ability to defeat the enemy means taking the offensive” .
In a similar way, the Department of Defense should take the offensive against climate change. While they are already taking significant steps to “green” the Department of Defense, these steps are reactive. The Department of Defense also needs to speak louder and more often on this issue, to help evangelize the United States and its allies on the imminent dangers presented by a warming planet.
Otherwise, the “Hot War” of the 21st Century might be our last war.
 With an annual budget of $582.7 billion, the Department of Defense is one of the largest government entities in the world. See “Department of Defense (DoD) Releases Fiscal Year 2017 President’s Budget Proposal,” Press Release, U.S. Department of Defense (Feb. 9, 2016), available at http://www.defense.gov/News/News-Releases/News-Release-View/Article/652687/department-of-defense-dod-releases-fiscal-year-2017-presidents-budget-proposal
 2014 Climate Change Adaptation Roadmap, U.S. Department of Defense (2014), available at https://www.scribd.com/doc/242845848/Read-DoD-report-2014-Climate-Change-Adaptation-Roadmap.
 “Historical Records May Underestimate Sea Level Rise,” NASA Global Climate Change (Oct. 19, 2016) (noting that scientists may have underestimated the average sea level rise due to ineffective placement of measuring instruments), available at http://climate.nasa.gov/news/2504/historical-records-may-underestimate-sea-level-rise.
 As Our Ocean Warms, Sea Level Rises, NASA Jet Propulsion Laboratory (accessed November 2016), available at http://www.jpl.nasa.gov/infographics/infographic.view.php?id=11298.
 “General Keys: The Military Thinks Climate Change Is Serious,” The Center for Climate & Security: Exploring the Security Risks of Climate Change (July 7, 2016), available at https://climateandsecurity.org/2016/07/07/general-keys-the-military-thinks-climate-change-is-serious.
 “The US Military on the Front Lines of Rising Seas,” Union of Concerned Scientists (accessed November 2016), available at http://www.ucsusa.org/sites/default/files/attach/2016/07/front-lines-of-rising-seas-key-findings.pdf.
 Explaining Extreme Events of 2014 from a Climate Perspective, Bulletin of the American Meteorological Society, Vol. 96, No. 12 (December 2015), available at http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-ExplainingExtremeEvents2014.1.
 “New Report Finds Human-Caused Climate Change Increased the Severity of Many Extreme Events in 2014,” Press Release, NOAA (Nov. 5, 2015), available at http://www.noaanews.noaa.gov/stories2015/110515-new-report-human-caused-climate-change-increased-the-severity-of-many-extreme-events-in-2014.html.
 2014 Climate Change Adaptation Roadmap, supra FN  p.4.
 See, e.g., Security Address, Executive Secretary Christiana Figueres, United Nations Framework Convention on Climate Change (Feb. 15, 2011), available at http://unfccc.int/files/press/statements/application/pdf/speech_seguridad_20110215.pdf.
 Brennan Delivers Remakrs at the Center for Strategic & International Studies Global Security Forum 2015, Press Release, U.S. Central Intelligence Agency (Nov. 16, 2015), available at https://www.cia.gov/news-information/speeches-testimony/2015-speeches-testimony/brennan-remarks-at-csis-global-security-forum-2015.html.
 National Security Implications of Climate-Related Risks and a Changing Climate, Department of Defense, Report Ref. Id. 8-6475571 p.14 (July 23, 2015), available at http://archive.defense.gov/pubs/150724-congressional-report-on-national-implications-of-climate-change.pdf?source=govdelivery.
 2014 Climate Change Adaptation Roadmap, supra FN  p.1.
 2014 Climate Change Adaptation Roadmap, supra FN  pp.1-2.
 The Art of War, Sun Tzu, Para. IV.5, available at http://classics.mit.edu/Tzu/artwar.html.