2010-09-04 04:55:40Possible new argument on climate sensitivity
Ari Jokimäki


Just today I bumbed to a situation where a climate change denier seems to think that climate sensitivity is only about carbon dioxide. This seems to result from the fact that climate sensitivity is often described as degree of temperature change from the doubling of carbon dioxide content. It seems that thinking is that if you can show that climate sensitivity is low, then you have proven that carbon dioxide is not warming the climate and you can go ahead explaining the climate change with something else. At this point our denier doesn't seem to realise that with low climate sensitivity, the climate change works rather badly even with the new explanation.

Paradoxically, the situation seems to be that clouds are causing the low climate sensitivity by causing a strong negative feedback, and then the clouds (with the assistance of cosmic rays of course) are also the alternative explanation for the climate change.

So, there are two paradoxes in this argument set; first the low climate sensitivity only applies to carbon dioxide but doesn't seem to be bothering other explanations; second the same reason seems to be working as a negative feedback (causing cooling when Earth tries to get warm) and a positive forcing (causing the initial warming that the negative feedback then constrains).

Now, thinking about my past discussions with deniers, it seems to me that this might actually be rather common situation among them but I haven't just realised it before. Have others noticed this? Are there already existing discussion covering this among SkS articles?

2010-09-04 13:31:40Have heard the argument
James Wight

Yes, I’ve come across this argument before. As far as I’m aware, the climate sensitivity for a particular forcing is the same no matter what the cause. I think it’s only by convention that it’s given in terms of warming per doubling of CO2. On the other hand, I know the pattern of warming is different depending on the cause, and I suppose that could lead to different feedbacks, so I’m not sure.
2010-09-04 14:53:15
Ari Jokimäki

Yes, there certainly might be some forcing specific differences in the climate sensitivity. For example, now the warming comes from carbon dioxide addition which probably changes the carbon-cycle feedback differently as it would be from some other forcings. But I think overall the climate sensitivity is the same for all forcings.
2010-09-04 21:36:35New argument idea
John Cook


Invariably whenever I give the 'climate sensitivity to doubled CO2' definition, people misinterpret it. So sometimes I give the disclaimer that any energy imbalance will cause a change in global temperature - it's just as valid to say climate sensitivity to a radiative forcing of 3.7 Watts/m2 as doubled CO2. But it's a pain having to stop and explain this everytime you discuss climate sensitivity.

Having a post and/or rebuttal on this topic would be good so that whenever someone brings up this objection, we can simply point them to this link. If you can frame a specific skeptic argument to rebut, preferably with an example webpage where the argument is articulated, then we can go with a rebuttal which is good as it then goes into the iPhone, Android and eventually Firefox plugin. If not, a blog post will also serve as a good place to link to.

So what I'm saying is if you want to write a blog post about this, please go right ahead - you have access to the Authors Admin so you can add the blog post and let me know when its ready to go live, I'll publish it.

2010-09-05 00:55:45
Ari Jokimäki


Well, the first step would be to hunt down a website clearly exhibiting this fallacy. I only have seen it in a forum discussions. This particular discussion was in Finnish so that's not helpful. I haven't followed any denier blogs or such, perhaps someone here knows a suitable reference for this?

The argument in the discussion I was involved in had to do with black carbon possibly causing half of the warming in the arctic so that then would have made the climate sensitivity lower (well, actually it was originally presented as evidence for negative feedback) because the effect of CO2 was lower there. Perhaps this rings a bell here and somebody points us to the origin for this argument.

I pointed out that the feedbacks don't care if the warming there is caused by CO2 or black carbon and then the denier started describing how the doubling of CO2 meant so and so much warming so if the warming from CO2 would be found lower than expected then the climate sensitivity would also be lower. This is the kind of moment where you have to scratch your head a bit pondering how to answer that. It's just so... well, stupid. I ended up answering by giving climate sensitivity definition with a link to wikipedia's basic description about climate sensitivity and stressing that it's not tied to CO2 specifically.

2010-09-05 06:39:47rebuttal
Dana Nuccitelli

I'm working on the advanced low climate sensitivity rebuttal now.  I've briefly touched on the points you raised, but will expand further in the introduction.  The temperature change at the surface is the climate sensitivity multiplied by the radiative forcing, regardless of the cause of that radiative forcing.  As John says, 3.7 Wm-2 is 3.7 Wm-2 whether it's caused by solar effects or greenhouse gases.

*Update* I just finished a draft of the rebuttal.  Have a look.

Advanced rebuttal to climate sensitivity is low 

2010-09-05 14:07:49Mistake in address
James Wight

dana1981, the address should be "www.skepticalscience.com/...", not "skepticalscience.com/..."
2010-09-05 15:45:33
Ari Jokimäki


Thank you, dana1981, that's excellent! Now (or, then when it has been published...) we have a place to link for this argument. :)

By the way, I found a website that makes this argument (and lot of others on the side...). If you want to give an example there, you can use this:


"A large aerosol cooling, therefore, implies a correspondingly large climate sensitivity. Conversely, reduced aerosol cooling implies lower GHG warming, which in turn implies lower model sensitivity."