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« Budget moments | Main | Avoid like the plague »
Wednesday
Mar202013

Zeke on climate sensitivity

Zeke Hausfather weighs into the climate sensitivity argument at the Yale Climate Forum (crossposted at the AGU). Like Skeptical Science before him, he chooses to base his analysis on a 2008 review by Knutti and Hegerl.

So what about climate sensitivity? We are left going back to the IPCC synthesis, that it is “likely” between 2 C and 4.5 C per doubling of CO2 concentrations, and “very likely” more than 1.5 C. While different researchers have different best estimates (James Annan, for example, says his best estimate is 2.5 C), uncertainties still mean that estimates cannot be narrowed down to a far narrower and more precise range.

The problem with this of course is that the science has moved on since Knutti and Hegerl and we now have all the papers like Aldrin et al and Ring et al that find much lower sensitivities than the IPCC range. Add in the warm bias from use of uniform priors and the old IPCC range of 2-4.5 is untenable.

When Hausfather moves on to policy he is equally shaky ground:

Ultimately, from the perspective of policy makers and the general public, the impacts of climate change and the required mitigation and adaptation efforts are largely the same in a world of 2 or 4 C per doubling of CO2 concentrations where carbon dioxide emissions are rising quickly.

The problem is that climate sensitivity of two gives you a cost of carbon that is much too low to justify most of the mitigation measures currently being deployed. Chris Hope put the cost of carbon for 1.6-degrees climate sensitivity at around $18/ton. The cost of mitigating emissions through wind power is more like $100. Even if you can justify wind with a climate sensitivity of 4, you will struggle to do so for 2.

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Reader Comments (26)

I thought the argument was that -- even with a lower climate sensitivity, you're still not accurately describing future warming. CO2 projections are that it will easily more-than-double by 2100, and thus a 2° sensitivity can still come out with 4°+ of aggregate warming.

Mar 20, 2013 at 12:11 PM | Unregistered Commentermorebrocato

Tea leaf science.

Mar 20, 2013 at 12:12 PM | Unregistered Commenternot banned yet

Not Banned Yet: But how else are you going to ascertain whether typhoo....ns are increasing in number and intensity!!

Mar 20, 2013 at 12:21 PM | Unregistered CommenterSteve Y

Models are wonderful (?). You program a climate model with a claimed CO2 doubling sensitivity and use the model to prove that CO2 causes AGW and climate change.

What if CO2 did NOT drive climate?

Hang on, present temperatures have stalled with rising atmospheric CO2 levels, the mid troposphere temperature anomaly cannot be found, heat radiating from the planet has remained the same since 1979 instead of the GHE fall predicted, Ice core data shows that temperatures rise before atmospheric CO2 levels.

So according to the scientific method we should alter the theory if empirical data shows it to be wrong.

So CHANGE THE THEORY. CO2 DOES NOT CAUSE AGW/CLIMATE CHANGE according to empirical data. And you can't use a model to prove a theory either.

Mar 20, 2013 at 12:29 PM | Unregistered CommenterJohn Marshall

The cost of mitigating emissions through wind power is more like $100.

It's not critical to your argument but does the above not assume that the technology performs remotely as claimed or does anything to "mitigate" (i.e. reduce) emissions? As has been demonstrated in a score of places, the jury is very much out on that one. (Recent examples include the Pat Swords/Kilchrenan Grannie Aarhaus Convention cases currently being considered by the UN.)

Whatever, I agree that the sensitivity issue is not, whatever AGW proponents argue, a trivial one, some sort of sideshow.

Mar 20, 2013 at 12:31 PM | Unregistered CommenterDaveB

The idea the the global average temperature (a notion entirely without physical meaning, so far as I can see) is linked to CO2 concentration by a simple logarithm formula, with only a single parameter to quantify, seems to me the new version of the Climate Change Religion.

Even many sceptics seem to believe in it.

When you try to track down the origin of the formula, it fades away like the Will-o'-the-wisp. About the nearest it comes to having a concrete origin seems to be the 1998 paper by Myhre et al, where logarithm formulas were fitted to the results from numerical models.

As someone said, it's turtles models all the way down.

Yet university professors engage in ernest debate about the numerical value of "climate sensitivity".

Is this any more "science" then medieaval discussions about the numerical value of the integer representing the maximum number of angels that could simultaneously dance on the head of a pin?

Mar 20, 2013 at 12:31 PM | Registered CommenterMartin A

Cherry picking across the climateverse boldy going forward cause we can't admit reverse!

Sorry, but these guys are fruitier than the man from del'monte in cherry picking, proxies, data sets and science articles.

Mar 20, 2013 at 12:50 PM | Unregistered CommenterJaceF

Colour me unimpressed.

He spends his time pondering the different ranges of estimated climate sensitivity and concludes that there is massive uncertainty.

So he wraps it all up with this clear statement of much greater certainty ("probably" and "likely"):

Just how warm the world will be in 2100 depends more on how much carbon is emitted into the atmosphere, and what might be done about it, than on what the precise climate sensitivity ends up being. A world with a relatively low climate sensitivity — say in the range of 2 C — but with high emissions and with atmospheric concentrations three to four times those of pre-industrial levels is still probably a far different planet than the one we humans have become accustomed to. And it’s likely not one we would find nearly so hospitable.


I think I could summarise and paraphrase this piece as follows:


"I know there is much debate about how sensitive our climate is to atmospheric CO2 concetrations and all available evidence suggests this is etremly difficult to tie down; we cant be sure within a particularly wide margin.

But despite that uncertainty I am pretty sure all potential outcomes are bad."


2/10.

Mar 20, 2013 at 1:36 PM | Unregistered CommenterGeckko

Those who use this number for prediction ought to be able to justify the idea that it is meaningful at all, never mind the right value. Now, what's the highest temp change over, say, three decades in the instrumental record? Can we even agree on that? Candidate decades?

Oh, the idea of producing a carbon price based on a climate sensitivity is a complete fantasy. It is not a good idea (IMHO) to accept warmist premises in order to undermine their arguments.

Mar 20, 2013 at 1:44 PM | Unregistered CommenterRhoda

Simply serves to illustrate that this, as in so many of the other areas of climate 'science', is all about policy-led 'science' and not science-led policy !!!

Mar 20, 2013 at 1:55 PM | Unregistered CommenterMarion

CO2 may be a potent agent, but on a immensely long timescale. The fact that it is difficult to discern its effect at multidecadal timescales implies that, if anything, it can only show up on multicentennial timescales. At that resolution it competes with other powerful agents, several of which remain poorly characterized.

A look at the past 8000 years or so at the Greenland ice core, for instance, reveals a millenial-scale stable pattern, with several sub-millenial scales swings, each of a magnitude larger than the present (c1850 onward) temperature rise. The colossal nature of these forces, both that produce the swings and the even larger one that brings it back in line, is evident only when we look at timescales of thousands of years. Zoom in on the same temperature course on to a 'policy-relevant' timescale and it is completely unclear that climate states with such differences as ~2C between them are in any way different from one another. CO2 may well be a player, but only at such scales, via the greenhouse effect and the biogeologic feedbacks.

This in turn means that attribution, especially actionable attribution, to CO2 at decadal timescales is essentially weak. The system is swamped by noise. Making economic arguments in such a scenario, is perhaps useful for career advancement of those who indulge in such things, but little else. As David Whitehouse points out, over the past 16 years or so, unknown forces of the exact same magnitude as was expected to play out from CO2 have acted on the climate system.

Who is going to legislate these forces?

It also pays to remember the history of the climate movement. The solutions offered by these guys - for the ozone crisis, global cooling, overpopulation, global warming, climate change, extreme weather ... are all the same. There is very little need to take their 'science' seriously. Clearly, they themselves dont!

Mar 20, 2013 at 2:00 PM | Registered Commentershub

'uncertainties still mean that estimates cannot be narrowed down to a far narrower and more precise range.' which means you can and some do spout any BS number , the higher the better , to support 'the cause '

Mar 20, 2013 at 2:20 PM | Unregistered CommenterKnR

Don't you all think its a bit funny to see the likes of Zeke & Mosher scrabbling around these days?

Mar 20, 2013 at 3:02 PM | Unregistered Commentermikef2

.....can I add Bjorn Lomberg to the list of peeps not knowing which way to jump too?

Mar 20, 2013 at 3:07 PM | Unregistered Commentermikef2

There is no science in "climate science". This is just nonsense.

Mar 20, 2013 at 3:15 PM | Registered CommenterPhillip Bratby

This is the equation they use to estimate sensitivity

T∆ = 5.35 x λ ln CO2p/CO2ref
Where CO2P is the current ppm in the atmosphere CO2ref is 280 and T∆ = 5.35 x λ ln CO2p/CO2ref
Where CO2P is the current ppm in the atmosphere CO2ref is 280 and λ is the climate sensitivity . For a doubling of CO2
T∆ = 5.35 x 0.8 x ln2
= 5.35 x 0.8 x 0.7
= 2.9667C
is the climate sensitivity. For a doubling of CO2
Quite why they chose 0.8 as the value for λ I’m not able to say. However what I can say is that we know T∆ and CO2P for our present state, they are 0.75C and 400 ppm respectively. So putting the observed state back into the equation we get:
T∆ = 5.35 x λ x ln400/280
0.75 = 5.35 x λ x 0.36
0.75/5.35 x.36 = λ
λ = 0.75/1.92
= 0.39
So let’s put that observed climate sensitivity into the original equation.
T∆ = 5.35 x 0.39 x 0.7
= 1.46C for a doubling of CO2
What am I doing wrong?

Mar 20, 2013 at 3:20 PM | Unregistered Commentergeronimo

"Just how warm the world will be in 2100 depends more on how much carbon is emitted into the atmosphere"

Simpletons think there is only one factor determining climate.

Mar 20, 2013 at 3:35 PM | Unregistered CommenterBruce

Climate sensitivity ~zero once water vapour concentration exceeds ~600 ppmV, about 3.3 % RH at 16 °C.
That's when it enters IR self-absorption and the GHE saturates. There is little if any CO2-AGW when it exceeds ~200 ppmV, its self-absorption threshold.

As for the climate modelling, it's a job creation scheme for those, the great majority apparently, whose physics knowledge is too limited to be allowed out of the computer modelling playpen!

Mar 20, 2013 at 3:41 PM | Unregistered CommenterAlecm

geronimo - check Rob Wilson's comment Mar 17, 2013 at 10:25 AM on the first page of comments on the "Rose in the Mail" thread. I think he is essentially agreeing with Rhoda that this single parameter view is worthless. "Calculating" it only gives it faux credibility. IMO.

Mar 20, 2013 at 3:42 PM | Unregistered Commenternot banned yet

"What am I doing wrong?"

Geronimo, the error in your calcs. is "T∆ = 0.75".

Since we Climate Scientologists know that CO2 causes much more warming than this, then the only possible conclusion is that the current temperature is wrong. This is clearly shown in the various IPCC diagrams that show that the current measurements are running approx. 0.5C below the 'real' temperature, but if we wait 30-40 years, it'll all work out on the end.

Mar 20, 2013 at 4:07 PM | Registered Commentersteve ta

Alecm,
Yes, exactly, well said and I couldn't agree more. It is all about the H2O on this planet. CO2 is a bit player. One only has to look at the profiles of various regional geographies, deserts, rainforests, savannas, and temperate forests to see that it is water that matters.

Mar 20, 2013 at 4:22 PM | Unregistered Commenterhum

Alecm - I understand the likelihood of a much reducing absorption level for CO2 as emission levels rise.

BUT can you point me to any web based information about self-absorption thresholds and the idea of a saturated GHE?

Mar 20, 2013 at 5:53 PM | Registered Commenterretireddave

The warmist position will always use the initial Hansen/IPCC range of Scenarios as the C of CAGW exists only in the high sensitivity, high feedback assumptions. To get them to redo their Scenarios with the recent work is to get them to invalidate their own positions.

Without high sensitivity and high feedbacks, the post-70s warming cannot be attributed mostly to CO2 warming. That means that the only argument about CO2 is about the INCREMENT on top of natural warming, and all costs have got to go towards this increment. The results-cost, not just benefit-cost, ratio collapses.

The Scenario range must narrow. But when it does the top, i.e catastrophic part, comes down; it doesn't go up. And with the only-partly CO2 kick, we have just knocked out man's technical ability to influence temperatures by 2100. And queers the financials Lord Lawson and others like to use to back up the "morally right" thing to do by going non-fossil.

Mar 20, 2013 at 6:30 PM | Unregistered CommenterDoug Proctor

2 years ago owsyerfather turned up on Lucia's site with his agenda driven analyses and here he is still banging the same old drum. He hasn't revised or revisited his stagnated theories in years.

Mar 20, 2013 at 8:32 PM | Unregistered CommenterStephen Richards

retireddave: http://www.thespectroscopynet.eu/?Physical_Background:Atomic_Emission_Lines_Shapes:Selfabsorbed_lines

Mar 21, 2013 at 8:28 AM | Unregistered CommenterAlecm

At one time Zeke was talking about developing a list of propositions that all sensible people could agree on. Maybe he's given up on that enterprise. Can we help him out?

1. There is a high school experiment that shows that with some simulation of earth atmosphere, if you add CO2, the temperature goes up. Without this, the climate warming dogma would be something like: the sky is made of cheese, and next Tuesday it's going to fall on us.
2. It has proven difficult to establish a definite link between man-made CO2 and temperature in the actual atmosphere of the actual earth. Man-made CO2 has gone up dramatically, in linear fashion; temperature has gone up, at least until recently when the increase levelled off, very modestly, and with lots of ups and downs. The correlation is weak.
3. Hockey sticks are nonsense. There was a Medieval Warming Period, non-man-made, and the 20th century warming is consistent with what has happened in the past.
4. A temperature increase of 1 degree C in 150 years is probably not something decision-makers need to concern themselves about.
5. Reducing CO2 emissions in Western countries makes no difference to emissions in developing countries, which are now the ones driving up global emissions.
6. There is some evidence that increased CO2 is "greening" the world by encouraging plant growth, while causing no provable negative effects. A small temperature increase probably helps plants absorb the CO2.
7. The search for dramatic "effects of climate change" is more or less a complete disgrace, shedding far more heat than light.

Mar 23, 2013 at 2:42 AM | Unregistered CommenterLloyd R

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