Yes, methane is one. But, at least in the US, it was only 10% emission in 2015, CO2 82%.
Who knows about CO2? Really? Yes, water vapor is plentiful, CO2 causes a major feedback loop:
https://www.skepticalscience.com/water-vapor-greenhouse-gas.htm
There's less methane than CO2 being produced, but as far as I'm aware it's a significantly more potent greenhouse gas, so still a concern. Water vapor is of course also a greenhouse gas, and water itself is the source of a couple feedbacks, positive and negative:
1. Decreasing ice will tend to decrease planetary albedo. Any other GHGs trapped in the ice will also be released.
2. Higher temps will produce more water vapor, and given that water vapor is a GHG, that can lead to further positive feedback as the article you link mentioned.
3. Increased cloud cover will tend to increase planetary albedo.