I agree, desalinization is another counterargument to the carrying capacity argument. An effectively inexhaustible source of water means that the tradeoff is primarily against economic activity, which sharply cuts against doomerist claims of land that simply can't sustain 40 million people. There are environmental costs to consider, but that's also (more?) true of temperature control in the 99% of the US that's less temperate than CA's primary population centers.