A few answers......
To Kal-el,
Although pollution/debris & waste tiles do not contribute to Global Warming, the following do:-
* total pollution points + 1 per citizen over 12 = % chance of pollution.
And Airports, Coal Plants, Factories, Iron Works, Manufacturing Plants, Offshore Platforms and Research Labs all generate between 1 and 4 pollution points each per turn (this can be altered in the editor).
Soooo....unlike Civ2, city shield production has
NO effect on generating pollution, but certain buildings and high population do.
* Global Warming depends apon the total
WORLD pollution output, from ALL civilisations.
* But in addition, each
nuclear blast greatly increases the chance of Global Warming....and a meltdown (or rebellion

) is classed as a nuclear blast.
It may seem odd that world climate change increases the more rebellions there are in the world, but as I said, just assume it's due to un-predictable random events.
To mrtn,
Meltdowns only occur if a city with a building that has the 'can explode or meltdown' flag ticked falls into disorder.
The longer the disorder lasts, the more chance of it happening.
(And, if EVERY building has this flag ticked, then the more buildings, the more chance of it happening.
With over a dozen of these buildings in a city, it will probably be a 100% chance)
