Yes, you read the thread title right. The idea is this - a global nuclear war, on a huge scale, even greater than the Great War, would result in immense devastation of plants and "green life" in general. Ensuing firestorms, forest fires and inferno would result in a huge amount of oxygen burning out, as it is necessary for ignition and sustention of fire. Radiation particles, dust, smoke etc. block out the sun, therefore limiting sun's light from reaching the surface of Earth in enough amounts for a continuous and stable photosynthesis in remaining organism which rely on chlorophyll for food production. That, combined with radiation destroys much, if not all, of Earth's plant life, therefore eliminating the main source of O2 on Earth (the "pre-War O2" burned out during the conflict). Without food, plants die. Without plants, not enough oxygen (not to mention food for herbivores and omnivores). Without oxygen, the biggest portion of life on Earth dies. Cyanobacteria are not enough to sustain life on a grand scale. Is such a scenario possible? 65 million years ago you had a huge firestorm that swept Earth almost clean of life, and resulted in (presumably) a long nuclear-sort of winter. However, there was no radioactive particles then, not like in the event of nuclear war. No black rain to kill almost anything it touches. The result was that majority of smaller animals survived, those which didn't require much food and were adaptable enough. So, does that mean that, realistically speaking, a worldwide nuclear war would result in the extinction of humankind on surface? As for those living in underground, would they die out due to this form of "asphyxiation" which would result as there is, basically, no strong, continuous source of oxygen on planet? Oxygen is a heavy element and tends to "fall down", so those living in underground shelters, metros and so on would probably have a source for a certain period of time, but how long? All this is highly hypothetical, borderline unrealistic, but I'd like to discuss it. Obviously, the topic goes beyond the realm of Fallout and into the heart of post-nuclear visions of future themselves (I feel so cool after writing this sentence), and therefore I posted it in GD rather than elsewhere. Please discuss. I have more thoughts I'll add later on.