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« Paris and the risk of green judges | Main | Hot, apparently »
Thursday
Jan212016

Real-world efficacies

BH readers have long been aware that low estimates of climate sensitivity based on observations are little affected by the pause and will therefore be little affected by this year's El Nino either. The discussion in this area will continue to focus on subjects like efficacies and aerosols. Marvel and colleagues are apparently formulating a response to Nic Lewis's critique, which is sure to be interesting. While we're waiting, I have been passed a preprint of a forthcoming Piers Forster paper in Annual Review of Earth and Planetary Sciences, which makes some interesting observations on the efficacy debate.

Shindell (2014) suggested that a higher transient efficacy of aerosol forcing could cause an underestimate of ECS in the historic record. Depending on the efficacy assumed for the aerosol forcing, the underestimate of ECS could be as much as 1.1 K (Kummer & Dessler 2014). The Shindell (2014) and Shindell et al. (2015) studies could only draw speculative conclusions due to a lack of forcing information within the historic CMIP5 model integrations analyzed. Marvel et al. (2015) explored this properly by computing efficacies and ERFs for individual forcing terms. They showed that within the GISS model, accounting for efficacies in the historical response could raise the implied best estimate of ECS from the historical period from around 2.0 K to around 3.0 K. However, my preliminary investigations (not shown) could not find any evidence of this effect in dedicated aerosol and carbon dioxide perturbation experiments within two climate models [Community Climate System Model version 4 (CCSM4) and Hadley Centre Global Environment Model version 2 (HadGEM2)]. Nevertheless, it could still be important, as the efficacies of different ERF mechanisms have not been properly assessed across models. The groundbreaking efficacy study by Hansen et al. (2005) needs updating: Efficacies need evaluating across other models and for transient change.

One has to ask though: if efficacies similar to those in the GISS model are eventually unearthed elsewhere, what does this tell us about the real climate system?

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Reader Comments (12)

"efficacies and aerosols", eh?!
There's a rude joke in there somewhere, Bishop, but I can't quite get a handle on it.
Apart from that possibility, it sounds like the same old same old!

Jan 21, 2016 at 11:38 AM | Registered CommenterMike Jackson

It must get frustrating, not to mention boring, when the settled science only leaves radiative forcing and aerosol forcing to explain everything, including the pause.

Jan 21, 2016 at 11:42 AM | Unregistered CommenterSchrodinger's Cat

Is there a. Internationally scientific definition of "forcing"?
What are its units. To me, an engineer it just seems to be a waffle term, used to show false superiority like other clique jargon with just a hint of threat.
It seems that, like a lot of climate terminology, it is vague with a meaning that can drift.

Jan 21, 2016 at 12:32 PM | Unregistered CommenterDoonhamer

Has anyone calculated the total forcing of the carbon footprint generated in proving the earth is warming?

Has any of it have made the slightest bit of difference?

Jan 21, 2016 at 12:50 PM | Unregistered Commentergolf charlie

'could not find any evidence of this effect in dedicated aerosol and carbon dioxide perturbation experiments within two climate models'

The models would behave as programmed. Models cannot divine the secrets of life.

Jan 21, 2016 at 12:50 PM | Unregistered CommenterGamecock

Doonhammer: my thoughts exactly. “Forcing” implies that it is an external factor, a factor alien to the system – but, no – is actually a part of the system! Who would have known?!

Jan 21, 2016 at 1:32 PM | Registered CommenterRadical Rodent

An unvalidated model is an illustration of a hypothesis. You won't find evidence in a hypothesis - apart from evidence about the mindset of its creator.

Jan 21, 2016 at 1:33 PM | Unregistered CommenterMartin A

Is there a. Internationally scientific definition of "forcing"?
What are its units. To me, an engineer it just seems to be a waffle term, used to show false superiority like other clique jargon with just a hint of threat.
It seems that, like a lot of climate terminology, it is vague with a meaning that can drift.
Jan 21, 2016 at 12:32 PM | Unregistered CommenterDoonhamer

Doonhamer. According to the IPCC radiative forcing is defined as follows:

"The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropo-spheric temperatures and state held fixed at the unperturbed values".

This is not the definition of a measurable physical quantity.

You can't measure the change in the radiation balance at the troposphere *after* the stratosphere has readjusted, but with the surface and tropospheric temperatures *held fixed*. The troposphere itself is an indeterminate thing. So yes, radiative forcing (as per the IPCC) cannot be measured. It can exist Only in climate models. It seems very strange that one of fundamental concepts of climate science cannot exist in the physical world only in computer models.

it is vague with a meaning that can drift.

Absolutely.

See "Observational determination of surface radiative forcing by CO2 from 2000 to 2010" http://www.pnnl.gov/publications/abstracts.asp?report=517436 for another meaning.

Jan 21, 2016 at 1:53 PM | Registered CommenterMartin A

Re forcings, a kittle-known factoid is that the IPCC gives estimates of negative land use forcing, but acknowledges it's not clear if such forcing is actually negative. Ij practice, this meant sensitivity estimates plugged in the negative values and probably erred on the high side. In Lewis&Curry 2014, assuming land use forcing centered on zero moved ECS from 1.65 to 1.55 iirc.

You know what you have to do if you want your model to 'estimate' high sensitivity: assume strongly negative land use forcing. Whether such a thing actually exists in the real world doesn't seem to matter.

http://climateaudit.org/2014/09/24/the-implications-for-climate-sensitivity-of-ar5-forcing-and-heat-uptake-estimates-2/

Jan 21, 2016 at 3:12 PM | Unregistered CommenterAlberto Zaragoza Comendador

Thanks, Martin A. Saved me the trouble.


After "efficacies" of forcing have been exhausted as a marketing term perhaps they'll get round to the much larger "efficacies" of feedbacks. It all seems spookily reminiscent of the pre-exponential term in the Arrhenius equation. This is sometimes taught to chemists as "the fudge factor". Or, in plainer words, the number you adjust to make results match the theory.

Jan 21, 2016 at 3:40 PM | Unregistered Commentermichael hart

ef·fi·ca·cy
ˈefəkəsē/
noun
the ability to produce a desired or intended result.

Jan 21, 2016 at 6:25 PM | Unregistered CommenterCurious George

I'm pleased to see you using a picture of Colossus.

Jan 22, 2016 at 12:27 AM | Unregistered CommenterWally

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