If India and Pakistan went at it and exhausted their stockpiles on eachother, Then yes- the likely death toll would exceed WW2- a single Hiroshima sized bomb, if dropped in the right city, might kill enough people to make up a good fraction of the WWII death toll- say %5, but it would come no where near to matching or exceeding the body count.

But an atomic bomb being used- ANYWHERE- will have horrific consequences, no matter what the death toll is. Human psychology is not logical... 2 million dead from being shot or hacked to death by machete does not begin to match the horror of 100,000 dead from a nuclear bomb in the human mind.

9-11 stunned us, now imagine turning on your TV one morning to see downtown New York City GONE, just smouldering rubble that no one will feel safe rebuilding in generations- how would that shatter our nation? How would we react?

How would we react seeing others in a nuclear exchange?

When, (not if), a nuke is next used, it will change the world for the worse.

As for the environmental impact... In a small nuclear exchange, I doubt the smoke will change much, but the radiation fallout on those down wind for thousands of miles will be a real problem... Chernobyl was pretty bad, this would be orders of magnitude worse.