Nuclear security is the set of procedures, practices or other measures used to manage risks from nuclear weapons and other nuclear materials.
Nuclear war is potentially the primary near-term anthropogenic existential risk. Nuclear war would probably not cause human extinction through the direct damage of an exchange. Rather, researchers are concerned about the potential for a nuclear winter: firestorms caused by the explosions could release particulate matter into the stratosphere, causing significant global cooling which would last for several years. This cooling would disrupt global agriculture, which would likely kill many more people than the initial exchange.[1]
However, there is some disagreement about how climate systems would react to the particulate matter and how much soot would actually be created (modern cities are potentially less vulnerable to firestorms than those during the cold war). As a result, it is unclear whether nuclear war poses an existential risk or a non-existential global catastrophic risk.
80,000 Hours rates nuclear security a "second-highest priority area": an unusually pressing global problem ranked slightly below their four highest priority areas.[2]
In The Precipice: Existential Risk and the Future of Humanity, Toby Ord offers several policy and research recommendations for handling risks from nuclear weapons:[3]