Climate change is undeniably a global problem, but the situation is especially dire for countries whose territory is comprised entirely or primarily of low-lying land. While geoengineering might offer an opportunity to protect these states, international consensus on the particulars of any geoengineering proposal seems unlikely. To consider the moral complexities created by unilateral deployment of geoengineering technologies, we turn to a moral convention with a rich history of assessing interference in the sovereign affairs of foreign states: the just war tradition. We argue that the just war framework demonstrates that, for these nations, geoengineering offers a justified form of self-defense from an unwarranted, albeit unintentional, aggression. This startling result places our own carbon-emitting activities in a stark new light: in perpetrating climate change, we are, in fact, waging war on the most vulnerable."We live in constant fear of the adverse impacts of climate change. For a coral atoll nation, sea level rise and more severe weather events loom as a growing threat to our entire population. The threat is real and serious, and is of no difference to a slow and insidious form of terrorism against us." -Saufatu Sopoanga, former Prime Minister of Tuvalu (Long and Wormworth 2012, 402) Kyle Fruh is an assistant professor of philosophy and humanities at Duke Kunshan University. His published interests include climate change ethics, the normative dimensions of commitments such as promises, and moral heroism.Marcus Hedahl is an associate professor of philosophy at the U.S. Naval Academy. His primary area of research involves second-personal normative relations within collective structures.