Bryan, remember that libel is only actionable if you publish your full name… the “Rahmstorf smoothing method” is documented in one of Rahmstorf’s references to the article, and the Matlab code available from its author Aslak Grinsted for the price of one email.

You would know that if you had any curiosity or interest in the truth. Yuck, you denialist fraudtors [compulsive hand washing]

Here is the quote (IPCC2007, SPM, p. 5):

There is very high confidence that the net effect of human activities since 1750 has been one of warming.6 {2.2}

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.7 It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica) (Figure SPM.4). {2.4}

During the past 50 years, the sum of solar and volcanic forcings would likely have produced cooling.

Here is the surface temperature record, according to GISS:

http://data.giss.nasa.gov/gistemp/graphs/

As you can see, the warming of the past 50 years didn’t actually begin until ~1976. Thus, the unprecedented warming of the past 50 years was isolated to the rise between 1976 and 1998. I don’t understand; what is the straw man argument here?

Finally, you wrote:

By selecting 1976 and 1998 start and endpoints, we are severely cherry-picking.

So… that’s what I said, too. Swanson really is, severely, cherry-picking, by drawing his trend-line through 1976-1998. So we agree? It is a mistake, and a strange mistake. Why did he do this?

Well, did Lindzen misinterpret it, or didn’t he? (Remember, we are talking about the earlier Tsonis et al. 2007 paper; Swanson & Tsonis 2009 seems to have been embelished a little with more apology to the IPCC that isn’t in the original paper). I say he didn’t misinterpret it, and I’ve actually read it.

(NB. That’s why it’s really not interesting at all, Ian Forrester, that Lindzen’s paper was published in Energy & Environment; I can think through this argument myself, because it’s actually not that hard, but thanks anyway.)

Here is the conclusion of Tsonis et al. 2007:

The above observational and modeling results suggest the following intrinsic mechanism of the climate system leading to major climate shifts. First, the major climate modes tend to synchronize at some coupling strength. When this synchronous state is followed by an increase in the coupling strength, the network’s synchronous state is destroyed and after that climate emerges in a new state. The whole event marks a significant shift in climate. It is interesting to speculate on the climate shift after the 1970s event. The standard explanation for the post 1970s warming is that the radiative effect of greenhouse gases overcame shortwave reflection effects due to aerosols [Mann and Emanuel, 2006]. However, comparison of the
2035 event in the 21st century simulation and the 1910s event in the observations with this event, suggests an alternative hypothesis, namely that the climate shifted after the 1970s event to a different state of a warmer climate, which may be superimposed on an anthropogenic warming trend. (Emphasis added.)

This paper directly, and unambiguously, challenges the “aerosol cooling” piece of the standard IPCC puzzle. Without “aerosol cooling”, it follows trivially that climate sensitivity is lower than what the IPCC have been advocating. In fact, it would presumably bring sensitivity much closer to Douglass et al. 2007 value, i.e. closer to data-at-face-value, and further from the model projections.

Tsonis, A. A., K. Swanson, and S. Kravtsov (2007), A new dynamical mechanism for major climate shifts, Geophys.Res. Lett., 34, L13705, doi:10.1029/2007GL030288.

http://www.uwm.edu/~aatsonis/2007GL030288.pdf

Again, the decision to draw the trend line through the 1976-1998 period, i.e. that period with the steepest gradient, is a really strange thing to do indeed. Wouldn’t you agree?

Response– The thing is that neither of these papers are formal attribution studies, nor do they have much to say about anthropogenic influences from a variety of forcings, or even to quantify varieties of internal variability. The object of both is their hypothesis of synchronized oscillation behavior, and I personally find very little of any of it convincing, but regardless neither are suitable references for claims that anthropogenic influences are not dominant warming mechanisms in the 20th century or will/won’t be in the 21st. I’ll also place criticism on the authors for wording which doesn’t really have much to do with their paper

As for the trendline, I don’t really have an opinion on it, you should ask someone in the statistical end of things (Tamino posted about this). By the way, I won’t be around for the next 3 days or so so I can’t moderate till then– chris

“That is, very little could be found there to reassure the IPCC that their Summary for Policymakers explanation of the so-called “unprecedented” global warming period 1976-1998 was caused entirely by increasing GHGs with 90% certainty (in fact, that it probably offset what would otherwise have been a period of cooling, IPCC2007, SPM, p. 5).”

I’m assuming you’re referring to the Synthesis report summary:

http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf

Perhaps you could find a quote in this report that supports what appears to be a strawman. The only quote that seems remotely related:

“Most of the observed increase in global average temperatures
since the mid-20th century is very likely due to the
observed increase in anthropogenic GHG concentrations.”

First, this doesn’t apply specifically to the more narrow 1976-1998 period you’re referring to. It’s from mid-century (we can assume 1950) through 2005 I believe.

Second, the statement says “most”, not “all”, which allows for a significant contribution from some natural factor during this period, which renders the statement fairly conservative, considering impacts such as volcanic and solar are likely to be that of slight cooling.

So if one is under the misimpression that PDO explains most everything, we have to note that the 1950 start point is during a PDO negative phase and 2005 (or 2008 if you’d like to extend it) is arguably in a PDO negative phase. It’s a near complete oscillation, yet compare 5-year means between these time periods. Attribution (or science in general) isn’t about coming to conclusions based on convenient correlations, though. We also have to study volcanic forcing, sulfate aerosols, and of course greenhouse gases (among other things) – things we can’t wish away.

The 1976-1998 period is an interesting study, since the warming during this period overshot most model predictions. For the sake of convenience, we can look at an early generation model from Hansen, using a higher climate sensitivity of more than 4 C. See Figure 2:

http://pubs.giss.nasa.gov/docs/2006/2006_Hansen_etal_1.pdf

Real-world emissions scenarios approximated Scenario B. Note the trend in the Scenario B model and compare it to the real-world temperature trend from 1976-1998. The real-world warming appears to be several times larger than the modelled warming. It would be wrong to conclude with confidence, however, that response to CO2 had been vastly underestimated in the model. By selecting 1976 and 1998 start and endpoints, we are severely cherry-picking. It wouldn’t be a surprise if subsequently real-world trends settled down closer to the modelled prediction over the following decade, especially considering how large an anomaly 1998 was.

Lastly, while I think it’s a serious effort done in good faith, I’m not convinced by the Swanson study. I think something like PDO (not as predictable to begin with as some might think), which is associated with somewhat more el Ninos during positive phase and la Ninas during negative phase, would have an affect on the trend during shorter transitionary periods, such as enhancing late 70’s warming or dulling the trend during recent years – not all that different from the 11-year solar cycle oscillation, which is currently in a long valley. I think it’s also another study in a long line of them that have been severely distorted for political purposes by contrarian types. I think many of them simply read what they want to read based on their own preconceptions. The RealClimate guest commentary by Swanson in that sense was long overdue. I thought Swanson’s comment is appropriate here:

“What do our results have to do with Global Warming, i.e., the century-scale response to greenhouse gas emissions? VERY LITTLE, contrary to claims that others have made on our behalf. “

These cycles do not contribute to the longer term trend, either because of how they physically operate or by definition.

I was alerted to the Tsonis et al. 2007 theory in a paper by Lindzen (2007, “Taking Greenhouse Warming Seriously”) where he interpreted the theory as such: “A very recent paper (Tsonis et al., 2007) suggests, in fact, that the surface temperature record can be accounted for by essentially superpositions of known oceanic fluctuations such as the Pacific Decadal Oscillations and the Atlantic Multidecadal Oscillations.”

I then read the Tsonis et al. 2007 paper and found that Lindzen’s interpretation of it was quite reasonable. That is, very little could be found there to reassure the IPCC that their Summary for Policymakers explanation of the so-called “unprecedented” global warming period 1976-1998 was caused entirely by increasing GHGs with 90% certainty (in fact, that it probably offset what would otherwise have been a period of cooling, IPCC2007, SPM, p. 5).

So Swanson’s appearance the other day at RealClimate came as a huge surprise to me. I was surprised that RealClimate would touch anything like this, other than to show that it was thoroughly discredited after enough big-name skeptics had started citing it (and I don’t think many have), and I was even more surprised to then hear Swanson’s view of the paper that there was no inconsistency with the IPCC version at all.

So I fixed upon the following issue, which appeared to be the slight-of-hand that allowed him to assert this apparently self-contradictory position: I saw that in that RealClimate post he just draws a straight line through the trend of 1976-1998, the so-called unprecedented bit, and then extends it all the way back to 1850, shows how it fits all the data in a vaguely convincing way, and then asserts that this is the underlying GHG signal. He also asserted that it wasn’t cherry-picking, and that I’d get the same line on any endpoints I could choose other than 1998-2008(??).

Here’s the problem: I am not a statistician, but in what sense can the rise of 1976-1998 be called “unprecedented” if it is the same trend that fits all the data all the way back to 1850? It wouldn’t unprecedented anymore, would it. It’d be quite normal.

I think this is a big problem, and I’m looking forward to your response.

All sorts of similar questions arise to this bizarre Swanson disavowal, and I am afraid, I just cannot believe he really believes himself what he’s just written. I guess that’s my earlier point about how you can say anything on a blog, even if you’re a published scientist, and get past the peer-review, i.e. it really cuts both ways.

Response– I don’t really buy into the Swanson/Tsonis paper, and actually I think most of it is pretty dicey. But I also agree with Swanson that it doesn’t represent an inconsistency with the much longer-term warming trend by greenhouse gases and I wouldn’t be surprised to see Lindzen misinterpreting it.– chris

I find it very odd indeed that you’ve chosen at this point to snip this comment on the basis of not following thread topic. I couldn’t actually work out what your thread was really about, on this occasion, because the first half is just a vent about your frustration in communicating with skeptics. And the point I was responding to was brought up firstly by yourself in a comment. Taken as a thread about communication, which it starts as, my post was quite on-topic, and it seems embarrassing to your friends at RealClimate, I would suggest being the real reason you have snipped it. I’ll re-post it at another blog, then, shortly.

Otherwise, keep up the great work; I enjoy reading your blog.