Yes. But there's ten trillion tons of water vapor in the troposphere, so, normally this wouldn't be a relevant amount. It's key that the volcano eruption lifted

Yes. But there's ten trillion tons of water vapor in the troposphere, so, normally this wouldn't be a relevant amount. It's key that the volcano eruption lifted the water vapor completely outside the weather layer, into the stratosphere. A marginal unit of water in the stratosphere is a lot more potent as a greenhouse gas, than the same unit in the troposphere. (I don't know the quantified values).