Help Required: Dodgy Claim by the CO2 Coalition?

[exchemist]

On another forum a climate change denier posted this graph:

At first glance it looks like no more than the expected exponential reduction in intensity with concentration of the absorber predicted by the Beer-Lambert law. Has anyone come across this being used as a counterargument to climate change science, is the implication true that further increases should have a proportionately lesser effect and what relevance does that  have to the models used to predict climate change?

 

 

[iNow]

https://royalsociety.org/topics-policy/projects/climate-change-evidence-causes/question-8/
 

“CO2 has its strongest heat-trapping band centred at a wavelength of 15 micrometres (millionths of a metre), with wings that spread out a few micrometres on either side. There are also many weaker absorption bands. As CO2 concentrations increase, the absorption at the centre of the strong band is already so intense that it plays little role in causing additional warming. However, more energy is absorbed in the weaker bands and in the wings of the strong band, causing the surface and lower atmosphere to warm further.“

[exchemist]

41 minutes ago, iNow said:

https://royalsociety.org/topics-policy/projects/climate-change-evidence-causes/question-8/
 

“CO2 has its strongest heat-trapping band centred at a wavelength of 15 micrometres (millionths of a metre), with wings that spread out a few micrometres on either side. There are also many weaker absorption bands. As CO2 concentrations increase, the absorption at the centre of the strong band is already so intense that it plays little role in causing additional warming. However, more energy is absorbed in the weaker bands and in the wings of the strong band, causing the surface and lower atmosphere to warm further.“

Thanks, that's helpful. 

What occurs to me about the graph is that they have chosen a scale and a range that makes the effect look as small as possible. We are in reality concerned with the range from 280ppm (the level at the end of the c.19th) to ~400ppm +/- 50 for scenarios in the recent past, today and the near future. So be useful, the graph should be scaled to show the effects within that range. On that basis it would be clearer that, even assuming the chart is correct, which I can't verify, the effect of an increase from 400-450ppm would be about 50% of the increase from 350-400ppm. So less rapid, sure, but still very substantial, and nowhere close to reaching some sort of asymptote of course. 

 

[studiot]

I don't follow the logic being presented.

If the heat flux to space decreases with increasing concentration how does that lead to less warming since that basic chem eng equation:

input  = output  + accumulation

surely applies ?

If the input remains constant, but the output decreases (heat flux to space) surely the accumulation (warming) must increase ?

 

1 hour ago, exchemist said:

Thanks, that's helpful. 

What occurs to me about the graph is that they have chosen a scale and a range that makes the effect look as small as possible. We are in reality concerned with the range from 280ppm (the level at the end of the c.19th) to ~400ppm +/- 50 for scenarios in the recent past, today and the near future. So be useful, the graph should be scaled to show the effects within that range. On that basis it would be clearer that, even assuming the chart is correct, which I can't verify, the effect of an increase from 400-450ppm would be about 50% of the increase from 350-400ppm. So less rapid, sure, but still very substantial, and nowhere close to reaching some sort of asymptote of course. 

 

Well done for reading the graph correctly in that most of it is redundant.  +1

 

For the last few million years co2 levels have been in the low hundreds of ppm.

It has been several thousand million years since levels were in the thousands of ppm.

Edited December 16, 2023 by studiot

[sethoflagos]

2 hours ago, exchemist said:

At first glance it looks like no more than the expected exponential reduction in intensity with concentration of the absorber predicted by the Beer-Lambert law. Has anyone come across this being used as a counterargument to climate change science, is the implication true that further increases should have a proportionately lesser effect and what relevance does that  have to the models used to predict climate change?

Check the y-axis: it is radiant heat flux to space. Why would anyone not expect this to be a flat line close to the corresponding value of insolation and independent of CO₂ concentration?

There are reasons: eg temporary accumulation of heat in the system while it's temperature increased to a new equilibrium level, for instance? If so then the shape of the flux to space curve is dependent on some assumed temperature gradient that quantified that accumulation rate, otherwise the flux to space would be ill-defined.

It is an issue of context framing. The graph, accurate or otherwise, provides an answer to a question that wasn't asked.

We are not interested in the value of the nett flux to space - that is already known with some accuracy.

Rather we are interested in the rate of temperature rise for the anticipated changes in CO₂ concentration: a figure the presentation implicitly assumes, and in doing so, denies its sensitivity to the variable in question. 

Deliberately dishonest. So no surprise there.

[swansont]

5 hours ago, exchemist said:

On another forum a climate change denier posted this graph:

At first glance it looks like no more than the expected exponential reduction in intensity with concentration of the absorber predicted by the Beer-Lambert law. Has anyone come across this being used as a counterargument to climate change science, is the implication true that further increases should have a proportionately lesser effect and what relevance does that  have to the models used to predict climate change?

 

 

The radiative forcing is logarithmic in the concentration, i.e. you get a certain effect from doubling the concentration. I’m not sure of the exact number in recent literature, but it’s a few watts each time you double. So each added molecule indeed has a smaller effect.

I haven’t seen this as a counterargument, but dishonesty abounds in such discussions. It’s incorporated in the models, so anyone claiming otherwise is pulling a fast one

[Ken Fabian]

An obvious issue to me is that the graph is based on relative "per molecule" impact, not atmospheric concentration, ie number of molecules. Less effect per molecule with a lot more molecules still adds up to warming. And the scaling makes a Watt/m² change look small and insignificant when it is not.

If you believed the interpretation of graphs like that by sources like CO2 Coalition global warming should already be slowing and the observed warming isn't actually continuing to accelerate - as if the observations must be wrong. But that graph isn't being used to inform people who have a good understanding, who might know that - it is intended to mislead people who do not. If enhanced greenhouse effect is self limiting and the effect is going to save us from having to do anything about it it should be saving us already and it isn't.

We don't have long running observations from space but over the time the Ceres satellite has been operational we observe that the net imbalance between incoming and outgoing energy has been rising. This is a graph based on Ceres satellite data -

 

 

Without delving deeper into how the graphs were calculated (which I have no wish to do) it isn't clear if this is theoretical (modeled) direct IR to space in the absence of all those complicating indirect flows to space.

 

 

Edited December 16, 2023 by Ken Fabian