On 17/09/2020 15:55, Alastair B. McDonald wrote:
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.

I'd have to agree with that analysis of Alastair B. McDonald's claims.

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.

Interesting but not relevant to the condition in that Arctic that you
mentioned, i.e. little forcing due to very low humidities there. Plus,
of course, that the sun angle in the Arctic is much different to that of
the tropics, leaving little contribution due to the low levels of
insolation.

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

That merely confirms that the temperature and the ice accumulation in
the Arctic hasn't changed for 10,000 years.

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

You need to account for the mechanism ('... once the ice melts...') that
kicks off your proposed raising of RH in the Arctic.

--
Spike