Debate Magazine

Weak "climate Denier" Argument.

Posted on the 10 December 2019 by Markwadsworth @Mark_Wadsworth

Prompted by Bayard's comment here about water vapour (and the logical impossibility of the CO2/H2O positive feedback effect, without which there can't be Runaway Global Warming. The arch-Alarmist website Skeptical Science admits that CO2 alone can't do much, it needs the CO2/H2O positive feedback effect as well), I did a bit of googling and stumbled across this.
There are at least a dozen sound reasons why I refuse to along with the "climate catastrophe" narrative, but this isn't one of them:
The effect of water vapor on temperature is especially important because of the United Nations Intergovernmental Panel on Climate Change (IPCC) claim that CO2 can cause catastrophic global warming. 

Because CO2 is not capable of causing significant global warming by itself, their contention is that increased CO2 raises temperature slightly and that produces an increase in water vapor, which does have the capability of raising atmospheric temperature. If that is indeed the case, then as CO2 rises, we should observe a concomitant increase in water vapour...
Agreed so far.
However, Figs. 9.3 and 9.4 show that water vapour (relative humidity) between 10,000 and 30,000 feet declined from 1948 to 2014.
That's his punchline? Here's his mistake - a decline in relative humidity can mean one of two things:
a) Less water vapour at the same temperature, or
b) Same amount of water vapour at a higher temperature.
So those measurements don't necessarily mean less water vapour.
From here, a nice chart:
So if we have 10g of water per 1kg of air at 15C, that's 100% relative humidity. If we warm the air to 25C, it's now only 50% relative humidity.
I'm not clever enough to reverse engineer the calculations, but I wouldn't be surprised if the average 6% fall in relative humidity over six decades means the same amount of water vapour and 1C higher average temperatures, and let's just accept the claim that the average atmospheric temperature has indeed increased by 1C over the last six decades (quite possibly true, quite possibly it's much more or less than that, or even a fall, I'm not sure it's a relevant metric, what matters is whether anything bad happens, down here on the surface).
I would be surprised if there was a significant increase in water vapour (you have to believe this if you are an Alarmist), but I'm not convinced there was a significant reduction, which is the basis of the argument under discussion.

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