On Thursday, 17 September 2020 at 09:21:00 UTC+1, Spike wrote:

Whenever I see 'HadCrut' I think of Clmategate.

Whenever I see Climategate I think of a scientist suffering from the timewasting tactics of a climate change denier.


More nonsense. When the temperature drops water vapour decreases and CO2 becomes the main greenhouse gas.

So we should be worried about water vapour rather than CO2. At what
level of water vapour does the crossover take place? How does that
relate to temperature?

There is no crossover point. At 0C there is virtually no water vapour (WV) and so the WV greenhouse effec is virtually nil, and the greenhouse effect depends on the CO2 concentration. As the temperature rises the concentration of water vapour increases until its effect overtakes CO2 and eventually it dominates, as it does in the tropics at sea level.

Note we are talking about local surface temperature, not global temperature.. Thus in the tropics, the snow-capped peak of Kilimanjaro is melting primarily because of the effect of increased CO2, not because the region is warming.

At 0C water vapour is insignificant, so over ice sheets CO2 is the main greenhouse gas. That is why the Arctic is warming three times faster than elsewhere. When the Arctic sea ice melts completely water vapour will take over the greenhouse effect and the NH will warm even faster!

Water vapour is part of a positive feedback loop. When the surface temperature rises (because of increased CO2) then more water is evaporated and water vapour increases. This raises the air temperature even further and produces more water vapour. This runaway effect only ends when enough of the water vapour condenses forming clouds which reflect away the incoming solar radiation.

When the Arctic sea ice has melted, water vapour will take over the greenhouse effect and the NH will warm even faster!

To sum it all up, CO2 concentration is not the only thing that affects global temperature. Solar radiation and ithe albedo from ice sheets and clouds play a major role. But the later depend on water vapour which depends on CO2.

HTH, Alastair.

In article ,
says...
At 0C water vapour is insignificant, so over ice sheets CO2 is the main greenhouse gas. That is why the Arctic is warming three times faster than elsewhere. When the Arctic sea ice melts completely water vapour will take over the greenhouse effect and the NH will warm even faster!


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.



--
Alan LeHun

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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.

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