My guess is perhaps Chris and company are looking for 'plausible' means to achieve climate change, instead of wormholes or rockets attached to the planet. However, this is a 'game', and secondly, it is sci-fi, so there is going to be 'some' element of the fantastic in there anyway. The question is what kind and how much?
Also, does Chris want the planet to have an edge on what the factions are able to do? Control heat, make rain, move masses of rock and earth, or plant forests (and how quickly do they grow?) If we are looking at short 'human like' lifespans for the races, then perhaps their agenda's would change, at least if they are an individual oriented society, though the hive mind races would probably stand better chances of achieving long term (centuries long) goals.
But Chris did say the races, at least the other AI races were very advanced, naturally in sci-fi, this is fun to play with new concepts and abilities. So it may be that the races have an edge on the planet. I am assuming some sort of push-pull between the two is preferrable for interesting and strategic gameplay?
I really like Zharmad's post and several by Cinth and Topper, but then again, i think i find myself agreeing more with the 'plausible' side, than the 'fantastic'. Of course if you had caught me ten years ago or so, i probably would have preferred the 'anatomic relay-inverted thing-a-ma-bob ray emitting thing'
Maybe of course Chris and company want something with both, the plausible and the exo-super-machine. It makes for a less static game and more different kinds of players.
I suppose to, that some of this is determined by the 'I'm in the first part of the game, and establishing a society-building like crazy, so these rules apply. Then moving on to ... well, we are now in the middle part of the game, where less building and more judicious decisions of where and what kinds of defense/offense we are using as we either encroach or are invaded by the other factions? Which lead to replacing some rules, maybe even most of them for a different kind of gameplay? And lastly of course moving into the end game, where we are probably at our strongest and perhaps weakest as well, strong armies, weak, almost population depleted cities? Formidable technology, but dried up resources? Maybe it is these shortages, or weaknesses that force us to 'co-operate' with some of the other races?
Oh as a quick note, I don't know if i heard this in reference to Civ-BE, or of Alpha-Centauri, so excuse the ignorance, but one of the 4x games out there was derided, at least in one of the reviews i read, of forcing the player into a player against everybody situation at the end of the game. So diplomacy and economic co-operation, was always short term, because at some point the player, or the other faction had to break away for the final, only one can win face off for the end. --- Anyway, my 'opinion' would be, please Arcen, don't do that if you can help it.
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As to adding something in this post to contribute to the theories to use for actual climate manipulation, either by the planet or by the player/factions, i would second the very fine points made my Zharmad, i like all the 'naturalistic' stuff.
Less the fantastical machines that adjust our orbit with no sense of how, other than, it can. Well, that is sci-fi isn't it? Haha, well, i suppose we have to have some of that, but maybe less of it would make the game more 'serious' than say, an RTS where anything goes?
I hope i haven't offended anyone, thanks for listening to my two cents. Wish i could contribute a 'theory' of my own, but to be honest, i'm not quite as learned as many here, so i go with what i favor.
Take care,
-Teal