Saturday, 12 September 2020

Clouding the issue

From Skeptical Science:

When skeptics use this argument [that water vapour is the strongest greenhouse gas], they are trying to imply that an increase in CO2 isn't a major problem. If CO2 isn't as powerful as water vapor, which there's already a lot of, adding a little more CO2 couldn't be that bad, right? What this argument misses is the fact that water vapor creates what scientists call a 'positive feedback loop' in the atmosphere — making any temperature changes larger than they would be otherwise.

How does this work? The amount of water vapor in the atmosphere exists in direct relation to the temperature. If you increase the temperature, more water evaporates and becomes vapor, and vice versa. So when something else causes a temperature increase (such as extra CO2 from fossil fuels), more water evaporates. Then, since water vapor is a greenhouse gas, this additional water vapor causes the temperature to go up even further—a positive feedback.

How much does water vapor amplify CO2 warming? Studies show that water vapor feedback roughly doubles the amount of warming caused by CO2. So if there is a 1°C change caused by CO2, the water vapor will cause the temperature to go up another 1°C. When other feedback loops are included, the total warming from a potential 1°C change caused by CO2 is, in reality, as much as 3°C.

From The Conversation:

Global warming is expected to cause changes in the amount of cloud cover, and the height and thickness of these clouds in the future, shifting the balance between the parasol and blanket effects of clouds. The knock-on effect this will have on temperature is known as cloud feedback. Climate change projections cannot ignore cloud feedback, as even relatively small changes in cloud properties can have significant implications for global temperature....

While we do know that clouds will likely amplify global warming, there is still a great deal of uncertainty about how strong this effect will be. Here climate models are of little help, as they can only simulate the bulk properties of the atmosphere over scales of tens of kilometres and several hours. Tiny cloud droplets form and evaporate in minutes. Models miss these small-scale details, but they’re needed for accurate predictions.

Do you notice that they are flipping back and forth between 'water vapour' (a gas) and condensed water droplets/ice droplets (clouds)? And throwing in CO2 as well, obvs.

Let's see if we can disentangle these and compare like with like...

It is not disputed that clouds have a noticeable and measurable effect on the weather/climate:
a) they cool the surface (and the air below them) by day by reflecting sunlight back up, and
b) they keep the surface (and the air below them) warmer at night up by reflecting infra red back down again.

Common sense and everyday observation tells us that overall, this is self-regulating and stable and areas with high relative humidity are cooler overall (with a smaller diurnal temperature range) than dry areas at the same latitude. Whatever warming effect water vapour has, it is completely reversed once it condenses to form clouds. (The latent heat of evaporation takes thermal energy from the surface and releases it higher up when water vapour condenses again, that cancels out.)

So the 'positive feedback of clouds' is nonsense, or else it would already have happened.
Water vapour

Water vapour (the gas) has very little warming effect (if it's even measurable). A clear night (with water vapour but no clouds) is much cooler than a cloudy night (where the water vapour has condensed).

And as with clouds, there can't be a positive feedback or else it would have already happened.

The Skeptical Science article confirms that water vapour is a far stronger 'greenhouse gas' than CO2. There's about ten times as much water vapour/water in the atmosphere as there is CO2, and water vapour absorbs and emits infra red at ten times as many more frequencies as CO2, so the fag packet calculation says the warming effect of water vapour is about a hundred times stronger than the warming effect of CO2 (admittedly with a huge margin of error).

But we have established that water vapour (the gas) has very little warming effect (if it's even measurable). And the warming effect of CO2 is only about one percent (with a huge margin of error) of the negligible warming effect of water vapour. In which case, the warming effect of CO2 is not even a rounding error.
Ho hum. Another epic fail by the Alarmists, they have neatly disproved their own point(s).


Bayard said...

This really is the weak point of the Gospel According to Michael (Mann). It relies on CO2 being the driver of AGW, because it is the only thing that makes the link between human activity and climate change and so make the whole belief system of angels (climate activists) and devils (Big Oil) and "you, too, can do your bit to save mankind" possible. It really is a denial of science to suggest that there can be a positive feedback loop where two identical forms of feedback have radically different effects.

James Higham said...

Is vapour yet a gas?

Mark Wadsworth said...

B, exactly.

JH, water vapour IS a gas. It is the gaseous form of water. Like ice is the solid form of water. Clouds are NOT water vapour, they are tiny droplets of liquid water (or ice).

JohnM said...

There's a more fundamental deceit going on.

The way this is presented is that the feedbacks are yet to happen. The implication being that the warming to date is only CO2 and that once the feedbacks kick in there will be a dramatic increase. That's the only way to get to catastrophe. Without feedbacks there is only CO2 and it's diminishing impacts (each extra unit of CO2 has less impact than the one before).

Mark Wadsworth said...

John M, yes the horrors are always in the future.

Nothing terrible has happened yet, in particular there have been hardly any widespread crop failures for decades (if you exclude a couple of deliberately engineered famines).

Famines are the only thing that worry me, a bit of flooding or damage to buildings? Local issues which can be fixed. Don't worry me.