"Global Warming" is a thing, but it has been around as long as Earth has been a water planet. The average temperature across the Moon is -15C, and the Earth would be too but for water being a greenhouse gas. So the average temperature actually is +15C.

But the oceans are all water, and even much of the land has water as ice or soil moisture. So the atmosphere is saturated with water, and any excess falls out of the sky (rain, snow, fog, etc.)

The reason CO2 and other greenhouse gases are a problem is they are not saturated, and accumulating.