The science is in and defence forces are resolute. Climate change will increase sea-level rise, drive up global temperatures and increase the frequency and intensity of extreme weather events. These impacts will limit the availability of food and water, undermine human health and devastate infrastructure and economies. This, in turn, could exacerbate existing tensions, increase societal instability, drive large scale migration and be a trigger for violent conflict. This is why military forces, and the security sector more broadly, are labelling climate change a “threat multiplier”. Extreme weather events have direct implications for military preparedness and the ability of the military to sustain itself, whilst greater instability, conflict and climate-induced migration will shape the types of roles and missions that militaries will conduct in the future.