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« Before the deluge | Main | It's the Atlantic wot dunnit »
Friday
Aug222014

Lewis on Chen and Tung

Nic Lewis emails:

I am sorry to see that Piers Forster has given what I consider to be an incorrect statement to the Guardian (p.19) regarding the new Chen & Tung Science paper about the Atlantic storing excess heat. He is quoted as saying: "Most importantly, this paper is another nail in the coffin of the idea that the hiatus is evidence that our projections of long-term climate change need revising down."

The paper very much supports the view of those scientists, including myself, who consider that natural variability in the ocean significantly affects surface warming trends on a multidecadal basis. It does not support the view that a reduction in the rate of increase in radiative forcing caused by aerosols, solar variations, reduction in stratospheric water vapour, etc. is the prime cause of the hiatus.

The press release for the new study states: "Rapid warming in the last two and a half decades of the 20th century, they proposed in an earlier study, was roughly half due to global warming and half to the natural Atlantic Ocean cycle that kept more heat near the surface." The new study supports Tung's previous (2013) conclusions by providing evidence from sub-surface ocean heat data, by filling in details of the cycle and by shedding light on the mechanism involved. If only half the warming over 1976-2000 (linear trend 0.18°C/decade) was indeed anthropogenic, and the IPCC AR5 best estimate of the change in anthropogenic forcing over that period (linear trend 0.33Wm-2/decade) is accurate, then the transient climate response (TCR) would be little over 1°C. That is probably going too far, but the 1.3-1.4°C estimate in my and Marcel Crok's report A Sensitive Matter is certainly supported by Chen and Tung's findings.

Since the CMIP5 models used by the IPCC on average adequately reproduce observed global warming in the last two and a half decades of the 20th century – a period over which uncertainty in aerosol forcing changes is small relative to the increase in greenhouse gas forcing – without any contribution from multidecadal ocean variability, it follows that those models (whose mean TCR is slightly over 1.8°C) must be substantially too sensitive. And since the IPCC projections of long-term climate change are based on those models, they must therefore need revising down, contrary to Piers' claim.

BTW, the longer term anthropogenic warming trends (50, 75 and 100 year) to 2011, after removing the solar, ENSO, volcanic and AMO signals given in Fig. 5 B of Tung's earlier study (freely accessible via the link), of respectively 0.083, 0.078 and 0.068°C/decade also support low TCR values (varying from 0.91°C to 1.37°C), upon dividing by the linear trends exhibited by the IPCC AR5 best estimate time series for anthropogenic forcing.  My own work gives TCR estimates towards the upper end of that range, still far below the average for CMIP5 models.

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Reader Comments (41)

Does this mean we can not reject the hypothesis that the feedback from CO2 level increases is zero?

Aug 22, 2014 at 12:53 PM | Unregistered CommenterLeon0112

"roughly half due to global warming and half to the natural Atlantic Ocean cycle"

Yes, that is reasonable.

"If only half the warming over 1976-2000 (linear trend 0.18°C/decade) was indeed anthropogenic"

Whoa! Whoa! Whoa!

How did we get from half the increase being global warming to half the increase being anthropogenic?

Any anthropogenic warming is an unknown sized *component* of that half of the 1976-2000 warming that is not from the natural Atlantic Ocean cycle

Aug 22, 2014 at 12:59 PM | Unregistered CommenterBruce Hoult

It has been said numerous times before so I repeat: Data is king, an opinion is just an opinion. The ratio between the two is heavily skewed towards the latter in climate science.

Aug 22, 2014 at 1:08 PM | Unregistered Commenteroebele bruinsma

Have I understood this correctly? Is it saying that the (supposedly perfect) climate models have been attributing twice as much warming to anthropogenic causes?

How is this not the headline in the newspapers?

Aug 22, 2014 at 1:09 PM | Unregistered CommenterStuck-record

Why don't we just face up to the fact that the sensitivity of the global climate to CO2 is as good as zero? There is no evidence to support AGW due to CO2 and the hypothesis has failed. It is all pseudo-scientific nonsense.

Aug 22, 2014 at 1:16 PM | Registered CommenterPhillip Bratby

NH temperatures respond to increases and decreases in the AMO, as Andronova & Schlesinger showed.

The AMO began recovering from the low point in the mid 1970's, and increased till around 2000. This coincided with global warming.

Since 2000, the AMO has been pretty much flat, and this has coincided with the standstill.

The AMO will likely begin to decrease in maybe 10 years time, and then we will see a drop in NH temps for the next 25 to 30 yrs.


http://notalotofpeopleknowthat.wordpress.com/2014/08/22/bbc-fail-to-understand-amo/

Chen & Tung seem to have confused the plateauing of the AMO with a drop.

Aug 22, 2014 at 1:29 PM | Unregistered CommenterPaul Homewood

Paul Homewood
Agreed ... almost entirely. The only fault I can find with this observation is the word "confused".
I am not suggesting that Chen and Tung are anything other than totally honest according to their lights (as almost certainly is Piers Forster); it is simply that none of them can leave go. The entire climate science community (at least the rabid warmist side of it) and their choir of Lewandowsky and Cook and Nurse and Ward, to name but several, are so buried up to their necks in the concept of AGW that they genuinely cannot conceive of a situation where things might be otherwise, even a little bit.
So while they are just about prepared to accept a pause (through gritted teeth and then with more caveats than you shake a stick at) anything more than that is simply incredible to them, literally.
I hope their university psychiatric departments are geared up for the day when even they have to admit that nature has outwitted them.
For them I have some sympathy; for the eco-activists and their co-conspirators in the political classes none at all.

Aug 22, 2014 at 1:52 PM | Registered CommenterMike Jackson

Looks like more scientists have dived in at the deep end - will they drown, or will that nice warm water pop them back to the surface.
Surely all these oceanic currents have existed and naturally varied for Centuries, long before anthropogenic carbon dioxide came on the scene.
The theory is that the more anthropogenic carbon dioxide emitted the more heat retained within the atmosphere. Question - why did it take until 1998 for this extra heat to disappear into the oceans?

Aug 22, 2014 at 2:15 PM | Unregistered CommenterShieldsman

Mike Jackson
"The only fault I can find with this observation is the word "confused". I am not suggesting that Chen and Tung are anything other than totally honest according to their lights (as almost certainly is Piers Forster); it is simply that none of them can leave go."

I don't doubt the honesty of any of these scientists. And to be fair to Chen and Tung, they do write in the paper that their mechanism does not allow the Atlantic ocean surface to start cooling before 2006. Moreover, Tung's 2013 PNAS paper shows the AMO signal (measured at the surface) not having materially declined since then, up to 2011.

Aug 22, 2014 at 2:18 PM | Unregistered CommenterNic Lewis

I must have missed the first nail in the coffin "of the idea that the hiatus is evidence that our projections of long-term climate change need revising down". What was it again? Since the Met Office has already revised down their estimates he needs to talk to them about it. AFAIK the main thing put in a coffin was Fosters technique for estimating climate sensitivity and he hammered the nails in himself on Ed Hawkins blog. His speculations are we must presume even more worthless than his dubious calculations, or as he put it, "wide uncertainty in climate sensitivity, making it hard to place a high degree of confidence in one best estimate". Well hard unless you make a habit of just making stuff up based on your gut feeling (and your reliance on grants) that is!

Aug 22, 2014 at 2:19 PM | Unregistered CommenterJamesG

More like a nail in the coffin of Piers Forster's credibility.

Aug 22, 2014 at 2:20 PM | Registered CommenterPaul Matthews

It is so very comforting to be reminded yet again that "the science is settled" and that the CGMs have the remarkable predictive properties they demonstrate time and again.

Aug 22, 2014 at 2:24 PM | Unregistered Commentertetris

Will we see a headline that 'it's better than we thought'? No need to answer that!

Aug 22, 2014 at 2:33 PM | Unregistered CommenterJamesG

Bruce Hoult


"roughly half due to global warming and half to the natural Atlantic Ocean cycle"

Yes, that is reasonable.

"If only half the warming over 1976-2000 (linear trend 0.18°C/decade) was indeed anthropogenic"

Whoa! Whoa! Whoa!

How did we get from half the increase being global warming to half the increase being anthropogenic?

Any anthropogenic warming is an unknown sized *component* of that half of the 1976-2000 warming that is not from the natural Atlantic Ocean cycle

Exactly.

Aug 22, 2014 at 3:10 PM | Unregistered CommenterSandyS

In the eyes of climate kooks like Forster, anything at all 'proves' that their obsession on high CO2 sensitivity is justified.
Heating? spot on! Cooling? Just delaying the inevitable. Results wildely divergent from actual measurements? Just wait for the other foot to drop, someday. Predicted drought/flood/storm experiences unchanged for >100 years? You clearly are a paid denialist!
The climatocrat maroon squad seems to filled with more wackjobs than a UFO convention sometimes.

Aug 22, 2014 at 3:41 PM | Unregistered Commenterhunter

Rapid warming in the last three decades of the 20th century, they found, was roughly half due to global warming and half to the natural Atlantic Ocean cycle that kept more heat near the surface.

Excuse me, but what 'rapid warming'? There's been very little warming around here, rapid or slow, nor any other places around the Atlantic from the temperature graphs I have looked at. All there has been is a recovery from the cold decades of the 50s and 60s - e.g.

"the warmest year in the extended Greenland temperature record is 1941, while the 1930s and 1940s are the warmest decades.” - source: http://www.cru.uea.ac.uk/cru/data/greenland/vintheretal2006.pdf

North Atlantic: JanMayen

Arctic also: 1880-2004 Jones et al dataset graph

Aug 22, 2014 at 4:35 PM | Registered Commenterlapogus
Aug 22, 2014 at 4:39 PM | Registered CommenterMartin A

Believing in CAGW has some equivalence to believing in ET because, although there is a consensus on the basic science (i.e. CO2 absorbs IR radiation and the likelihood of life on Earth-like planets is high), there is as yet no convincing evidence to show any physical manifestation of it here on Earth.

So, next time you hear people saying we need to radically alter our economies to combat CAGW, think about how credible it would sound if they were asking us to combat ET instead... actually, I'd rather fund SHADO than the IPCC :-)

Aug 22, 2014 at 4:52 PM | Unregistered CommenterDave Salt

The headline should read,

New paper says that anthropogenic global warming is only half of what was previously thought

Aug 22, 2014 at 5:43 PM | Unregistered CommenterSpeed

@ Mike

"their choir of Lewandowsky and Cook and Nurse and Ward, to name but several"

You forgot Mikey Mann ... although that's hardly the point.

If I were a real 'climate scientivist' I would have to feel nothing but shame and profound depression that this bunch of dissembling vagabonds and rogues are accepted as the 'best' public face of my science.

Sad. Eh, RB?

Aug 22, 2014 at 5:55 PM | Unregistered CommenterJerryM

Nic Lewis:

I don't doubt the honesty of any of these scientists. And to be fair to Chen and Tung, they do write in the paper that their mechanism does not allow the Atlantic ocean surface to start cooling before 2006. Moreover, Tung's 2013 PNAS paper shows the AMO signal (measured at the surface) not having materially declined since then, up to 2011.

Clarity followed by charity. Class. Thank you.

Aug 22, 2014 at 6:14 PM | Registered CommenterRichard Drake

Piers Forster writes

"Most importantly, this paper is another nail in the coffin of the idea that the hiatus is evidence that our projections of long-term climate change need revising down."

This sounds more like "Blind Faith" rather than deductive logic.

In fact one of the authors, KK Tung, clarifies exactly which conclusion is to be drawn from his paper on Judith Curry's Blog quote:

If one is blaming internal variability for canceling out the anthropogenically forced warming during the current hiatus, one must admit that the former is not negligible compared to the latter, and the two are probably roughly of the same magnitude. Then when the internal cycle is of the different sign in the latter part of the 20th century, it must have added to the forced response. Assuming the rate of forced warming has not changed during the period concerned, then the two combined must be roughly twice the forced warming during the last two and half decades of the 20th century.

I would be interested to know how Piers Forster manages to reach the opposite conclusion !

Aug 22, 2014 at 6:21 PM | Unregistered CommenterClive Best

Clive Best,
Like most of the climate obsessed, Piers Forster arrives to the discussion with his conclusion in hand. Pesky things like facts and conclusions are not important to him.

Aug 22, 2014 at 6:37 PM | Unregistered Commenterhunter

I await the authors actual empirical data that 'proves ' their claims of missing heat . Because until they its speculation that 'proves ' nothing at all but they can write models to get results form input which themselves are guess work and based on assumptions the authors make about 'should be ' happening .

Still has we told that any idea of a 'hiatus 'is a fossil fuel funded denialist lie , or have been for a very long time. I may have to wait a long time.

Aug 22, 2014 at 6:39 PM | Unregistered CommenterKNR

Given that:

1. we know most studies are flawed

2. there is no quality control process in science

3. no one will ever replicate this study

No person with a desire to employ logic and rationality should ever give a whole lot of credence to a study like this or any other. What an odd contagion of irrational faith it is that has spread throughout our scientific communities! This must be what it would be like to watch lemmings leap off a cliff, but in slow motion.

Seems strange that a non-scientist such as Steve Mc should have more genuinely scientific thoughts in a day than a 100 climate 'scientists' have in their careers. Not just strange -- devastating to the long term health of science as an institution.

Aug 22, 2014 at 7:07 PM | Unregistered Commenterstan

Piers Foster writes:

"Compare climate change to a train trundling across America. Some way down the track, we are not sure how far, the bridge is out and disaster looms. Do we want to be the ones to sit back and watch the train wreck, or do we want to be the hero?"

He obviously thinks that a bridge is out and that he and his fellow Yorkshiremen have a good shot at stopping the train! Being a hero is nice.

Aug 22, 2014 at 7:12 PM | Unregistered CommenterPolitical Junkie

Clive Best --
The quotation from Dr Tung about the 50-50 attribution of the late-20th c. warming rang a bell. I found a similar comment from a couple of years ago:

If a natural cycle (NAO) is enough to outweigh the “greenhouse effect” during its current cooling phase, by symmetry wouldn’t one expect that it was responsible for over half of the positive temperature change during its warming phase?

Heh. The difference is that Drs Chen & Tung have gone well beyond merely noting the presence of natural variability, by hypothesizing a mechanism, which is progress if confirmed.

Aug 22, 2014 at 7:25 PM | Registered CommenterHaroldW

Bruce Hoult said,

"How did we get from half the increase being global warming to half the increase being anthropogenic?

Any anthropogenic warming is an unknown sized *component* of that half of the 1976-2000 warming that is not from the natural Atlantic Ocean cycle"

Well said.

One can only wish that more people, climate scientists especially, were capable of applying had critical thinking skills.

Aug 22, 2014 at 7:33 PM | Unregistered CommenterMike Singleton

Increased Man made CO2 is a negative feedback.

http://sunshinehours.wordpress.com/2014/04/15/could-co2-have-lowered-the-rate-of-natural-warming/

Aug 22, 2014 at 8:18 PM | Unregistered CommenterBruce

Nic,

I fully agree with the points you make, with one small exception: My own results show that a transient climate response (TCR) of around 1.1 °C or even a little less is not out of the question, though your 1.3 to 1.4 °C is well within reasonable uncertainty levels. A relatively simple energy-balance model with these lower sensitivities is able to fit observed temperatures over the 1850-2000 time period as well as or better (in many cases much better) than any of the CMIP5 GCMs, yet also agrees with observed temperatures fairly closely over the 2000-2013 "pause" time period where the GCMs are diverging rapidly. This implies to me that the pause is not unexpected, but is instead mostly an artifact of too-high sensitivity in the GCMs (though I do have an indication that there is probably a secondary contribution from longer-term natural variability). In any event, the natural-variability vs. sensitivity-based projections of temperatures to 2020 are significantly different, so this argument should be pretty well resolvable with five to eight years of additional temperature observation data. Keep up the good work.

Aug 22, 2014 at 9:50 PM | Unregistered CommenterKeith Jackson

Keith,

Thanks.

" My own results show that a transient climate response (TCR) of around 1.1 °C or even a little less is not out of the question"

I agree that a TCR of 1.0 to 1.1 °C is by no means out of the question, particularly if aerosol forcing turns out to be lower than the IPCC AR5 best estimate. As you say, we will have a better picture with another five to eight years' data. However, I fear getting a much narrower range for TCR (and for equilibrium climate sensitivity) will also require a substantial reduction in the currently large uncertainty range for aerosol forcing.

Aug 22, 2014 at 10:48 PM | Unregistered CommenterNic Lewis

I would quibble with just one of Nic's otherwise excellent observations.
The CMIP5 models may reasonably reproduce the roughly 1975-2000 temperature anomalies to which they were tuned. But they do not reasonably reproduce actual temperatures. The spread is roughly +/- 3C. See Dr. Curry's input to the APS 2014 review for a graphic of that, available at www.aps.org/policy/statements/upload/climate-change-transcript.pdf. That means key processes like ice formation in clouds, cloud formation as a function of dew point, and evaporation/specific humidity as a function of temperature, and so latent atmospheric heat, are all off--a lot. This is best seen in model comparisons of ice in clouds. None of CMIP5 outputs resemble the actual global patterns sensed by satellite. See J. Geo. Res. 117: D14105 (not paywalled).
As interesting as the Chen and Tung paper is concerning the Atlantic meridional overturning thermohaline circulation and it's contribution to observed GAST, they cannot overcome such basic model inadequacies. Is covered explicitly in an essay illustrating specific climate model inadequacies in a forthcoming book on energy and climate.

Aug 23, 2014 at 1:10 AM | Unregistered CommenterRud Istvan

There is a clear correlation between AMO and NH temperatures.

http://notalotofpeopleknowthat.wordpress.com/2014/08/22/correlation-of-the-amo-with-nh-temperatures/

And as NOAA state

" When the AMO decreases, as from 1950 to 1975, global warming may appear to be reversed. When the AMO increases, as from 1975 to the present, the global warming (red) is exaggerated. "

http://www.aoml.noaa.gov/phod/faq/faq_fig2.php

The AMO has essentially been flat for the last decade, and this has contributed to the pause. But when it starts to go down, it will have a downward effect on temperatures for 25-30 yrs.

Aug 23, 2014 at 10:52 AM | Unregistered CommenterPaul Homewood

Just to clarify my point on the AMO.

What matters is not so much the AMO phase, i.e warm or cold, but the direction of travel.

The AMO hit rock bottom in the mid 1970's, but as it began to recover, temperatures responded, despite the fact it remained in negative territory till the mid 1990's.

Aug 23, 2014 at 11:30 AM | Unregistered CommenterPaul Homewood

Nic - if you are following this thread...

I don't think you are allowed to write "natural variability ... affects ... trends". Not when it's your field of study.

A yachtsman could casually observe that sometimes the sea was warmer than at other times and describe this as "natural variability".

But a self-described scientist needs to be more honest. If you don't know all the factors that affect trends then say so in as many words.

Aug 23, 2014 at 3:22 PM | Unregistered CommenterJack Hughes

Jack Hughes:

"I don't think you are allowed to write "natural variability ... affects ... trends". Not when it's your field of study."

There's nothing dishonest here. Obviously, no one knows all the factors that affect multidecadal trends in climate variables or the mechanisms involved in them. I was following conventional usage in referring to natural (internal) variability, which includes all factors apart from forcings that are external to the climate system.

Aug 23, 2014 at 3:50 PM | Unregistered CommenterNic Lewis

The sun is a voltage which varies regularly over 24 hour and annual periods depending on latitude and irregularly over longer periods. The ocean is a capacitor connected to the voltage with a variable resistor, the atmosphere, connected across it. Each band of latitude has its own capacitor and resistor which receive there own voltage through a series of step down transformers. Each of these is also connected to its neighbours with zener diodes with variable trigger voltages controlled by knobs. The knobs are located in the monkey pen at the zoo.
Calculate the average temperature of the resistors.

Aug 24, 2014 at 12:14 AM | Unregistered CommenterGeoff Cruickshank

"Have I understood this correctly? Is it saying that the (supposedly perfect) climate models have been attributing twice as much warming to anthropogenic causes?

How is this not the headline in the newspapers?"

Because, Stuck-Record, nobody believed it in the first place. The pronouncements of climate scientists have always been held to be true only in a purely Pickwickian sense.

Aug 24, 2014 at 12:59 AM | Unregistered CommenterUncle Gus

"Why don't we just face up to the fact that the sensitivity of the global climate to CO2 is as good as zero? There is no evidence to support AGW due to CO2 and the hypothesis has failed. It is all pseudo-scientific nonsense.

Aug 22, 2014 at 1:16 PM | Registered CommenterPhillip Bratby">>>

Try telling that to the lukewarmist regulars on this blog. They'll accuse you of weakening their so called 'sceptical' message. They claim that warming due to CO2 is a fact, although they say it's not as high as the alarmists claim. But still find it impossible to give a calculated figure for the amount of warming expected from their lukewarmist theories. In other words, yet more hand waving, although in this case from the faux sceptical lukewarmist camp.

Aug 24, 2014 at 2:25 AM | Registered CommenterRKS

Nic,
Interesting. I agree with you that Forster's comment is incorrect - in fact I can think of some stronger language to apply to it, but I will resist the temptation.

On the other hand, the Chen & Tung analysis seems simplistic. They are over-attributing the natural surface temperature oscillations to the AMO in my view. The quasi 60 year oscillation in temperature represents at a global level the weighted summation of the temperature cycles apparent at a regional or ocean basin level.

From Chambers et al 2012:- "We examine long tide gauge records in every ocean basin to examine whether a quasi 60-year oscillation observed in global mean sea level (GMSL) reconstructions reflects a true global oscillation, or an artifact associated with a small number of gauges. We find that there is a significant oscillation with a period around 60-years in the majority of the tide gauges examined during the 20th Century, and that it appears in every ocean basin. Averaging of tide gauges over regions shows that the phase and amplitude of the fluctuations are similar in the North Atlantic, western North Pacific, and Indian Oceans, while the signal is shifted by 10 years in the western South Pacific. The only sampled region with no apparent 60-year fluctuation is the Central/Eastern North Pacific. "

It makes no sense to me to view the problem as a sort of competition between the Atlantic and Pacific. The common element in all this is the change in atmospheric circulation patterns which occurs with some limited predictability on an approximate 60 year periodicity, and this has a global effect. It is not possible to model variations in the AMOC, a primary control on the AMO, as a purely mixing-driven phenomenon. It needs an energetic forcing, and this comes from variation in winds. This is a known phenomenon on seasonal and interannual scales. The indices also suggest that this must apply to multidecadal scales. Similarly, the relative intensity and frequency of ENSO events is controlled by the equatorial trade winds. Strong westerlies - a reversal of the normal Pacific trade wind - bring on an El Nino event, and there is no question that teleconnections extend this to make the effect global.

The warming periods are associated with an increasing strength of the zonal circulation at mid latitudes and a poleward shift by a few degrees of all the pressure extrema belts. The cooling phase shows an increasing weakening of the circulation. These various regional oscillations all have common cause in my view - forced change in the atmospheric angular momentum.

How one explains the temperature oscillations makes a significant difference to how one accounts for them in order to estimate the underlying climate sensitivity to a radiative forcing. The common assumption that one can eliminate the temperature oscillations and then estimate sensitivity on the secular temperature series is very unsafe, I believe.

Aug 24, 2014 at 5:13 AM | Unregistered CommenterPaul_K

Paul,

Thanks for your comment. I agree that things are complex, and Chen & Tung may indeed be somewhat over-attributing the influence of the AMO. But I think that their new paper provides useful insights into what is going on, even if it is not complete. It is worth also reading Dima & Lohmann (2007), where they forward possible natural physical mechanisms for the AMO. Delsole et al (2011) also found an internal multidecadal pattern in global SST, without using AMO related information. They employed a sophisticated statistical method based on maximising average predictability time, to separate forced and unforced variability in SST. Although their method applies globally, the IMP they detect (their Fig. 4) is remarkably similar to the standard NOAA detrended-AMO index.

Given the uncertainty as to the influence of multidecadal internal quasi-oscillations, in particular the AMO, I think that there is merit in using as long a period as reasonably possibly for estimating climate sensitivity. Conveniently, the period from the 1860s and 1870s, when volcanic forcing was low, to the last ~20 years, when volcanic forcing was also low, both appear to coincide with the upper part of the AMO oscillation.

BTW, congratulations on making excellent comments about volcanos and TCR at Isaac Held's blog.

Aug 24, 2014 at 9:47 PM | Unregistered CommenterNic Lewis

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