What would happen if a modern nuclear weapon was exploded?

The immediate effects of a nuclear explosion are blast, heat and ionizing radiation in proportions depending on the type of weapon and where it was exploded - in the air, under ground or under water, for example.”
(Christy Campbell, Nuclear Facts, Methuen, Toronto, 1984.)

These are the effects of an average one-megaton bomb  -- 
70 times the power of the bomb dropped on Hiroshima in 1945:

At ground zero, a crater 300 feet deep and 1200 feet in diameter would be produced;
All life and structures would be pulverized;
The fireball in the centre of blast would have temperatures hotter than the sun.
Lethal radiation would spread for thousands of miles.
Firestorms would cause superfires, and there would be temperatures over 1000 degrees C.

Deaths would result from:

• burns, asphyxiation, heat
• injuries due to falling structures
• cancer and leukemia
• diseases due to immune deficiencies,
• the electromagnetic pulse destroying life support systems
• local and global fallout causing radiation sickness
• starvation

Verbatim ICJ Record, including testimony given by the Mayors of Hiroshima and Nagasaki to the International Court of Justice, 1995.

BLAST EFECTS

The Effects of Nuclear Weapons, compiled and edited by Samuel Glasstone and Philip J. Nolan, 3rd Edition, prepared and published by the U. S. Dept of Defence and the Energy Research and Development Administration, 1977 online at: http://www.princeton.edu/~globsec/publications/effects/effects1.pdf

Nuclear Blast Mapper: http://www.pbs.org/wgbh/pages/amex/bomb/sfeature/mapablast.html

Details on Nuclear Weapons blast effects: http://www.pbs.org/wgbh/amex/bomb/sfeature/effects.html

The NYT gallery of photos from 1945 to 1952 on "Capturing the atom bomb on film", military photos of explosions during that period of time.

Deposition of the Mayor of Hiroshima to the International Court of Justice: http://www.city.hiroshima.jp/shimin/heiwa/deposition-E.html
(Note: the bomb dropped over Hiroshima was 12-15 kilotons. Today strategic missiles are armed with thermonuclear devices rated with a blast of up to1.5 megatons –100 times more powerful than the Hiroshima bomb. Bombs of 50 megatons have been detonated in tests, and those of twice that power have been rumoured. )


NUCLEAR EXPLOSIONS and CLIMATE CHANGE

"Local Nuclear War, Global Suffering" Scientific American article by Alan Robock and Owen Brian Toon, at
http://climate.envsci.rutgers.edu/pdf/RobockToonSciAmJan2010.pdf

Nuclear Darkness website, created by Steven Starr www.nucleardarkness.org