Can AI come up with an alternative to Hb that we can genetically engineer babies to have before the imbalance ambient air is lethal? Probably. But no one is working on it. It will probably affect behavior & intelligence in imperceptible ways long before humans see it as an issue worth pursuing. And then we depend on animals... we're going to replace the whole ecosystem with genetically engineered variants that can thrive in higher CO2/lower O2 environment (are we going to also change our dependence on the Krebs cycle which needs O2) ? No, I don't believe that is realistic. Supply chains will be long gone, humanity too, before then. Or, we could just tax the f out of fossil fuels. No. Brainer.