I honestly wish they wouldn't put such a mechanic in the game at all. My own disagreements with the theory are beyond the scope of this forum, but let's look at Civ 6's implementation as an example. The theory is the CO2 is the global thermostat. CO2 goes up, temperature goes up, polar ice caps melt, all natural disasters get more frequent and severe. But what if CO2 goes down? Shouldn't that mean temperature goes down, polar ice reforms, natural disasters become less frequent and less severe? But in Civ 6, it's a one-way mechanic. Even if you pour all of your empire's industry into carbon capture and drive the CO2 numbers well into the negatives, none of the process reverses. According to the theory, we should be able to induce a disaster-free utopia, or even a "snowball" Earth if we take it far enough. Scientifically speaking, if we drop the concentration of atmospheric CO2 below 150 ppm, photosynthesis stops, and all multicellular life on the planet dies. If we're going to model the theory, then model the theory.
From a game design perspective, it's counter-intuitive. It's only used as a restraint on human industry in Civ 6. Instead of encouraging you to secure the win, they produce crippling penalties for using all those cities you built up all game and for using a modern military to make it harder for you to finish out that scientific or domination VC. This might be fine if the goal was to serve as an anti-snowball mechanic, to give players who fell a bit behind a chance to keep it competitive at the end, but the penalties are applied to all players in the game, so there's no catching up. And worse, it's a mechanic over which the player has no control. If a player is particularly concerned about triggering the mechanic and uses every strategy at his disposal to make his own CO2 contribution nil, he still receives exactly the same irreversible penalties as everyone else. From a game play perspective, that's a really terrible design to punish all players for one or two player's strategic choices/trade-offs. They get the benefits, you get the penalties, and again, it's a one way mechanic, so once anyone triggers the penalties, everyone is stuck with them.
It's a terrible concept. It's unbelievably unfun to play with. If I could disable it without disabling the rest of the expansion's features I would.
I agree that it should be reversible if enough carbon capture happens. It would be interesting to allow it to go below industrial levels and cool the earth, although I'd argue a minimum level below which carbon capture projects are impossible makes more sense - I'd at least hope humans are smart enough not to carbon-capture our way into oblivion.
The "even if you contribute zero, you are still affected" mechanic is consistent with actual global warming. Is that too realistic for gameplay purposes? Maybe? There
are diplomatic influence penalties for being a heavy carbon emitter, so there are some benefits to being a low/non-emitter. At the same time, it's a valid strategy to build floodwalls and go all-in on emitting carbon - if your rivals have more low-lying cities than you do, it's arguably even a good strategy. I'm rolling coal in my multiplayer game, calculating that investing in cultural buildings is more likely to achieve victory than the diplomatic benefits I could achieve by reducing my emissions.
Making it optional is something I'd have no issue with, just as espionage was optional in IV. But despite its imperfections, and wishing for better in VII, I appreciate the attempt to model it in VI.
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Which reminds me of something else new in the last 8 years. The importance of natural gas as a form of energy. In VI, you can accumulate large stockpiles of strategic resources - coal, oil, uranium. In the real world, we saw that Europe's reserves of natural gas were measured in months, and once trade with Russia plummeted, there were serious concerns about whether the reserves would be sufficient for the winter of '22-'23.
Civ VI gives +10 stockpiles for every resource for every tier of military building. This could be expanded on significantly in VII. Some resources are relatively easy to stockpile - make a big pile of coal on the ground, for example. I saw one of those the other day in real life. But liquid resources, like oil and natural gas, often require dedicated infrastructure, and the rate of consumption can make it challenging to have years (turns) worth of stockpiles if there isn't a significant effort to build that out.
Hearts of Iron IV makes the effort to model this with oil - you get a little bit of storage with general infrastructure improvements, but if you really want to build a major reserve beyond what your own resources or trade partners can provide, you have to spend significant resources building that out.
Something like this in VII could add leverage to petro-states, and, if natural gas is added as a resource (which I'd argue it probably should be), natural gas states. Do you import cheap natural gas from your large neighbor, stick with your polluting coal reserves, or build out nuclear or renewable resources? Beware if you choose the former, and there is a
zeitenwende (changing of the times, when your provider ceases to be reliable).
