On September 27, the 195 member countries of the United Nations Intergovernmental Panel on Climate Change (IPCC), supported by the work of thousands of scientists from around the world, released its Fifth Assessment Report. Even for a military man like me, the latest scientific evidence on global warming makes for a chilling read.The scenarios set forth in the report indicate that if the world continues on its current track, burning more and more fossil fuels and increasing the levels of pollution in our atmosphere year after year, global average temperatures could rise by four degrees Celsius by the end of the century. That amount of warming would cause sea levels to rise, displacing tens of millions of people worldwide. Moreover, it would disrupt weather systems, destroying harvests and threatening populations with droughts, floods, and storms of ever-increasing intensity. It would also place a massive strain on global water resources.When I was a major general in Bangladesh’s military, my job was to avoid conflict while planning for the worst-case scenario. And, from the perspective of the military, the consequences of global warming constitute the worst-case scenario.My country, Bangladesh, is a frontline state in the face of climate challenges. It is ground zero for the effects of climate change and the security implications they present. In Bangladesh, climate change is not a theory, a story, or a concept; it is a way of life. As I write, lives are being lost to rising seas, water shortages, and the resulting diseases. Gradual and large-scale displacement of people is taking place, and every day the threat is increasing.Bangladesh, like India, China, and Pakistan, depends for its water on the glaciers of the Himalayas. Those glaciers are disappearing, and the world’s most populous countries – all with significant military capabilities, including nuclear weapons – will find themselves facing an existential crisis if too little water is available. We know that this will happen, and we know that  people do not always make the wisest decisions when faced with deprivation of an essential resource.When I meet with my colleagues at the Global Military Advisory Council on Climate Change – generals and admirals from around the world, all with career-long experience in military planning and operations – I am struck by the similarity of our concerns. All countries of the world are experiencing changes that are destabilizing communities and increasing security concerns. Diseases are spreading, wells are drying up, storms are smashing cities and destroying crops, and rain is either a distant memory or an acute danger.Many of these effects are being felt most intensely in regions – such as South and Central Asia, or West and East Africa – where security is already fragile. Climate change does not respect borders and we can already see the impact of global warming at play in many internal crises. When a river that crosses a border or flows through disputed territory becomes a matter of life and death, or food prices skyrocket because a local crop has failed (or even because a major global producer redirects its exports to its own hungry people), conflict can start and spiral out of control very quickly. Militaries need to plan for these scenarios and work with politicians to ensure that they never arise.In global security circles, we often speak of the "international community.” Climate change is the ultimate global challenge and global threat, and the global community must meet it together. We cannot have our separate attitudes and plans.People are dying now. Food prices are rising now. And soldiers are on streets around the world dealing with the effects of climate change – from natural disasters to social unrest. We cannot risk the local, regional, and global security threats that climate change will generate if politicians, civil-society groups, industry, academia, the military, and all other sectors of society do not act together and act now.World leaders should read what the IPCC has to say and take heed. Climate change is the greatest global security threat of the twenty-first century, and if we do not tackle it now, the worst-case scenarios will be our reality.ANM Muniruzzaman is Chairman of the Global Military Advisory Council on Climate Change.www.project-syndicate.org