Final answer:
The estimated total yield of around 4,000 MT for all nuclear bombs is a rough estimate; actual yields range from 0.1 kT to 20 MT per warhead, and the largest nuclear detonation ever was approximately 50 MT. Total yield is subject to change and is classified.
Step-by-step explanation:
The statement that the total explosive yield of all the nuclear bombs in existence currently is about 4,000 MT is a simplified estimate and may not accurately reflect the existing global nuclear arsenal. Nuclear weapons vary greatly in yield, with energy yields measured from about 0.1 kilotons (kT) to upwards of 20 megatons (MT) for single warheads. Historical records show that the largest nuclear test, the Tsar Bomba detonated by the Soviet Union, had a yield of about 50 MT alone. The contemporary arsenal is diverse, and while there are disarmament efforts, the exact total yield is classified. It is also subject to change due to ongoing arms control treaties and dismantlement of warheads.
A megaton (MT) is a unit of explosive energy equivalent to one million tons of TNT. Nuclear bombs create energy through fission and fusion reactions, and their yields are expressed in comparison to the explosive power of TNT. The estimated explosive yield of the entire nuclear arsenal is a subject of debate and varies according to different sources.