Afaik it is a strong greenhouse gas, but under normal circumstances the amount of water vapor in the global air is more or less the same so it won't matter that much.
Now we don't live in normal circumstances, but in a society that hasn't given economic value to an environment that is essential to it's survival. And so it happens like in France where nuclear energy couldn't be used anymore because there wasn't enough water in the rivers for the process anymore, during a particularly hot summer.
Essentially water vapor is one of the runaway feedback loops for cilmate change, more vapor means more greenhouse effect, means warmer, means more vapor, etc. This works until the air is saturated. Climate is driven by a bunch of those complex feedback loops and includes tipping points (e.g. particular big ice structures melting) so predicting how exactly it will pan out isn't trivial.
A side effect of more water vapor is also that storms get stronger and rain falls worse.
> nuclear energy couldn't be used anymore because there wasn't enough water in the rivers for the process anymore
That's a deformation; production had to be reduced (not stopped), not because there was not any water anymore, but because the exhaust water temperature would have been over the threshold for ecosystem stability. The plants could have been run at full power if we were OK with toasting the shellfishes.
Now we don't live in normal circumstances, but in a society that hasn't given economic value to an environment that is essential to it's survival. And so it happens like in France where nuclear energy couldn't be used anymore because there wasn't enough water in the rivers for the process anymore, during a particularly hot summer.
Essentially water vapor is one of the runaway feedback loops for cilmate change, more vapor means more greenhouse effect, means warmer, means more vapor, etc. This works until the air is saturated. Climate is driven by a bunch of those complex feedback loops and includes tipping points (e.g. particular big ice structures melting) so predicting how exactly it will pan out isn't trivial.
A side effect of more water vapor is also that storms get stronger and rain falls worse.