On Thursday, 17 September 2020 at 14:54:36 UTC+1, Alan LeHun wrote:
Not making sense here. You are saying the Arctic is warming 3 times
faster than elsewhere because there is no WV forcing in the Arctic (it's
all CO2 forcing).

Then you are saying that once there is WV forcing it will warm even
faster.

What I am saying is that the greenhouse effect from water vapour is saturated in the tropics. Any increase in CO2 has very little effect there because the temperature has already been maxed out by the water vapour producing clouds. Of course it is more complicaed than that because there are no clouds in parts of the sub tropics e.g. the Sahara Desert, and clouds can be produced by orography not just convection.

In the cryosphere there is, in effect, no water vapour until the ice melts, so the warming is due to CO2. However, once the ice melts the positive feedback from water vapour will kick in and temperatures will soar as they did at the start of the Holocene (end of the Younger Dryas) when the sea ice in the GIN (Greenland, Iceland, and Norwegian ) Seas disappeared. See

https://cdn.britannica.com/s:1500x70...s-addition.jpg

Note the ice concentration on that diagram is land ice produced by snow from water vapour evaporated from the ice free GIN Seas.