Wouldn't greenhouse gases turn earth into a wet greenhouse? A parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30

Wouldn't greenhouse gases turn earth into a wet greenhouse? A parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30 °C, but only 8 grams of water per cubic meter of air at 8 °C. So isn't it possible that runaway methane would turn Sahara green again?