You would see a significant increase in radiation related deaths. The number would depend on what altitude the weapons detonate. If they are impact fused that would be far worse than any air burst (fallout from water bursts can be REALLY nasty).
Low number? 10 million early deaths.
I don't see a way for both superpowers to have a mutual accidental launch. In fact the only way anything close to this can happen is some sort if accidental triggering of Russian/Soviet Deadhand System. Even that is unlikely as to my understanding there is a man in the loop still with Deadhand.
ERCS requires a valid launch authorisation from at least 2 seperate launch crews in seperate locations. As this happens in a time of peace with no increase in tensions then the launch officers are definately going to call in and ask for verbal confirmation. At the very least they are going to want to know where to retarget their missiles.
I call ASB.
What is ASB?
Not even underwater explosions came close. Barely a blip outside the immediate area. Actually, googling 'tsunami bomb', the US did some research on what would be necessary to set of a tsunami. It requires a lot more precision than just causing a giant splash at one point. That just produces normal waves. For a tsunami you need an organized displacement of large volumes of water - at the very least the impacts would have to be timed in a very precise way in order to properly build up on each other.in regards to tsunamis, didn't the U.S. test nuclear devices as large as 25 megatons in the Pacific Ocean? Did they produce any substantial localized tsunamis?
A 1968 research report sponsored by the US Office of Naval Research addressed this hypothesis of coastal damage due to large explosion-generated waves, and found theoretical and experimental evidence showing it to be relatively inefficient in wave-making potential, with most wave energy dissipated by breaking on the continental shelf before reaching the shore.[4]
Not even underwater explosions came close. Barely a blip outside the immediate area. Actually, googling 'tsunami bomb', the US did some research on what would be necessary to set of a tsunami. It requires a lot more precision than just causing a giant splash at one point. That just produces normal waves. For a tsunami you need an organized displacement of large volumes of water - at the very least the impacts would have to be timed in a very precise way in order to properly build up on each other.