Tuesday, 10 December 2019

Weak "climate denier" argument.

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.


PJH said...

" So if we have 10g of water per 1kg of air at 15C, that's 50% relative humidity. If we warm the air to 25C, it's now only 50% relative humidity."

I think your proofreader needs some more coffee Mark....

Mark Wadsworth said...

PJH, thanks, I have corrected :-)

Physiocrat said...

Something we all know: during the day, it is cooler if it is cloudy. At night, it is cooler if the sky is clear. Clouds reflect radiation. When, horror of horrors, you travel in an aircraft, it is dazzlingly bright when you have got above the clouds. Water droplets in clouds are like cats eyes in the road.

Radical Rodent said...

There is also the idea that there is no such thing as “greenhouse effect”, so “greenhouse gases” are irrelevant anyway.

See here: http://theendofthemystery.blogspot.co.uk/2010/11/venus-no-greenhouse-effect.html and here: https://youtu.be/1Y_n283fYbc

I have not seen either of these debunked, just various ad homs against the authors.

Physiocrat said...

Greenhouses work as follows: radiation from the sun heats up the objects inside, which in turn warm the air in contact with them. This warm air cannot escape because it is contained by the glass, and is trapped inside. On a clear night the temperature in the greenhouse falls quickly due to radiation through the glass. That is why it is necessary to have blinds inside the roof to prevent this night-time radiation.

The so-called 'greenhouse effect' is ascribed to absorption, at night, of radiation from the surface of the earth by greenhouse gases and its subsequent re-radiation in all directions ie 50% of the captured radiation is returned back towards the surface of the earth. However, given that all the carbon dioxide in the atmosphere would form a layer less than 4 metres deep, and that carbon dioxide absorbs infra red radiation in just a few narrow frequency bands, I would like to see calculations which show that this process can have any significant effect.

Mark Wadsworth said...

P, yes. Water vapour cancels itself out, has warming effects and cooling effects.

RR, of course, this used to be common knowledge, somehow it was deleted from the text books. All that matters it atmospheric pressure, not the constituent gases.

P, that's why they have to invent the co2-h2o feedback.