My first question is what are the probability of nuclear war...
That depends on the ongoing political situation.
Currently a large-scale nuclear war seems unlikely; The USSR no longer exists, so USA-USSR tensions are no longer present. Russia is essentially a capitalist system so there is no real ideology clash there. China is officially communist, but its economgy relies heavily on the west so going to war would not be advantageous.
As long as the US and Russia maintain their absurdly large cold war-legacy stockpiles, they'll be able to dominate all other nuclear powers (the US and Russia have warheads in the thousands; other nuclear powers have maybe hundreds of warheads).
A regional war? Regional wars can be prevented by the same factors that prevent wars between superpowers. There's plenty of tension between India and Pakistan, but I doubt any sane Pakistani or Indian would wish to commit nuclear war.
Due to the generally high population density in India, a nuclear attack would likely be extremely damaging.
As for North Korea, well, the insanity certainly exists there for potential nuclear deployment. But I have a feeling the retribution to NK- most likely in the form of conventional warfare- would be extremely major.
Israel is widely believed to have nuclear weapons, though no other power in the region has nuclear weapons. Syria and Iran have been suspected to have nuclear weapons programs, and the extremely strong Iranian anti-Israel sentiment could be cause for a regional conflict.
South Africa had a nuclear weapons program, but dissasembled it.
So: Where is the "I don't know when or if nuclear war will happen" option? :shifty:
My second is what is the smallest theoretical explosion a warhead could produce...
Small. Depends on what you mean by "warhead". Also depends on whether you want to situate a rocket engine around your bomb; designs such as the Daedalus study or ICAN studies detonate small fusion or fission/fusion propulsion units in succession using electron beams, lasers, or small amounts of antimatter. Nevertheless, such a massive structure would be absurd to use as a weapon, and would wrap itself beyond silly to be used as a low-yield weapon.
Another option is a nuclear isomer (essentially excited atomic nuclei) such as Hafnium-178M2, which has an energy density of 1 326 000 MJ/kg. This means that if you replaced the mass of the explosive within a 20mm shell with pure Hf-178M2, you would have the energy equivalent of over 2 tons of TNT. New fun-size death and destruction!
Of course, the problem is that Hf-178M2 releases all of that energy over a period of decades. We don't know how to get an instant energy release, or even if an induced energy release is practically achievable. There's even been considerable [ame="http://en.wikipedia.org/wiki/Hafnium_controversy"]controversy[/ame] surrounding supposed attempts at induced energy release from Hf-178M2.
Of course, the problem for a man-portable weapon firing such a large amount of energy is that you'd probably have to max-out your range. And your accuracy would disappear. But it would certainly make for a nice portable artillery analogue; probably not gigantic amounts of destruction, but rather conventional amounts of destruction delivered unconventionally.
My third is how will we use nuclear weapons that doesn't involve MAD(Mutualy Assured Destruction)...
I feel that you're thinking here, "Gee, I wanna see some nukes go off!".
I don't want to sound funny here, but if you're thinking like that, you should probably stop.
The first step to thinking about nuclear weapons at all is to imagine yourself on the recieving end of them. Imagine if your state, your city, your town was hit in a nuclear attack. Imagine what would happen to the inhabitants of your town. Imagine what would happen to your friends and family. Imagine what would happen to
you.
Then you'll be glad that MAD exists.
In English it even has a nice-sounding acronym to remind us how crazy the idea of such mass-scale destruction is.
My fourth is what long term effects will such warfare have on the environment...
Over geological timescales, I have a feeling the Earth won't really notice it. There's a long-standing conception of nukes slagging entire continents, and that's really silly with the nuclear stockpiles we've seen in history so far. Cities, population centers, strategic targets, they'll be hit hard, but places that are in the middle of nowhere, rural areas, etc will pretty much get by unharmed save for some radioactive fallout.
In a hypothetical major nuclear exchange between two superpowers in the northern hemisphere, the southern hemisphere probably wouldn't be negatively affected at all save for slightly increased radiation levels.
I roughly calculated once that in 30 minutes, the Sun delivers four times the amount of energy to the Earth as the detonation of 20 500 warheads at 1 megaton each. If the Sun doesn't slag the planet in 30 minutes, a fourth of that energy certainly won't.
Of course, you have things like smoke and CO2 created by fires started by the fireball, aerosols introduced into the atmosphere, nitrogen oxides created in the high temperature of the explosion, etc. This could all cause damaging short-term climatic effects, but just as with for example a large-scale volcanic eruption, the planet will recover relatively quickly.
As for humans, people love to see them going extinct. But we're actually extremely adaptable organisms. We're like... the ape-cockroaches. If any species would survive after the worst of hypothetical nuclear apocalypses, it's us.
If we manage to keep it that way for another century, till last witness of any war is dead, then there will never be a war again, i believe.
The opposite is probably true; I think that WWII is still fresh on the collective psyche of humanity, even after 60-70 years.
Forget what war is like, the effect it has on people, families, societies, countries, continents... and then all you have is a bunch of kids playing videogames and thinking "HURZ COOL I BLEW HIS HEAD OF HEADSHOT LULZ". And then when that happens, people end up being eager to go to war because they'll think it'd be
fun, or
cool, or whatever.
And that's when millions of people would die.
Now, I'm not saying we should start wars to... prevent... wars... just that we must instill a proper understanding in people, so they don't go off thinking that they can throw darts at a map, to choose some country which they want to practice their death-and-destruction skills on...
EDIT:
we are no more capable in predicting what the planet Earth and her meagre inhabitants will be doing in 1,000 years than our prehistoric ancestors would have been at predicting the plot of last week's Doctor Who episode.
That is pretty insulting both to your prehistoric ancestors and to humanity's ability to predict the future. I wouldn't stand much of a chance of predicting the plot of a Doctor Who episode either, even though I actually know what Doctor Who
is.
Already musings of things such as interstellar spacecraft today, are better than the Leonardo's suggestions of flying machines in the 1300s. We know inexorably more about physics and technology; we could build a spacecraft that could visit another star, we just don't have the infrastructure or exact know-how yet.
People keep going on about how our "technological advancement is constantly increasing", and to be honest it gets pretty boring. One could just as easily say that we've picked the low-hanging technological fruit and new inventions are becoming increasingly more difficult to implement. Just because we're entering an information revolution and Moore's law is driving the development of computers doesn't mean our technology is evolving into incomprehensible Star-Trek crystals-and-togas magic. Various things in history increased in performance in similar patterns, and then stopped at a point, only to advance slowly and slightly more after that.
I'm not saying computers are a doomed technology or we'll all still be using today's PCs by 2035, but in general terms, it's an interesting consideration. Look at the advancements around the first half of the 20th century- radio, radar, internal combustion, flight, jet engines, the maturation of firearm technology, nuclear power and weapons, the beginnings of spaceflight...
What can we compare those with in our era?