On Dana1981’s Meaningless ENSO Exercise at SkepticalScience

Dana Nuccitelli (Dana1981) of SkepticalScience has redefined El Niño and La Niña years in a meaningless exercise to show that the warming trends of El Niño, La Niña and ENSO-neutral years are comparable. It confirms his limited understanding of El Niño-Southern Oscillation (ENSO) and its impacts on global surface temperatures, or his willingness to misrepresent them, or a combination of the above. Dana also made some flawed assumptions with his new definitions of El Niño, La Niña and ENSO-neutral years. “Flawed assumptions” is the nicest way I can phrase that.

INTRODUCTION

Dana Nuccitelli went to great lengths to redefine El Niño and La Niña years and to create a misleading graph (gif animation), Figure 1, in his SkepticalScience post Was 2012 the Hottest La Niña Year on Record? According to his new definition of El Niño, La Niña and ENSO-neutral years, global temperatures warmed at similar rates for the three phases of El Niño-Southern Oscillation (ENSO).

Figure 1 – Dana Nuccitelli’s Meaningless Graph

NOAA defines an El Niño and La Niña year as:

A La Niña (El Niño) year is defined here as occurring when the first three months of a calendar year meet the La Niña (El Niño) criteria as defined by the CPC.

Dana Nuccitelli apparently did not want to use NOAA’s definition for his meaningless graph. And he definitely couldn’t have used the older version of NOAA’s Oceanic NINO Index with NOAA’s definition of El Niño and La Niña years because 2012 would not have qualified as a La Niña year.

SO DANA1981 REDEFINED EL NIÑO, LA NIÑA, AND ENSO-NEUTRAL YEARS

Dana Nuccitelli writes:

Rather than define a somewhat arbitrary threshold for a La Niña/El Niño year (i.e. based on the size of the index and number of months exceeding a certain threshold) or limiting the analysis to one ENSO index, I first took the average of the three indices mentioned above (ONI, MEI, and SOI, accounting for the fact that positive SOI indicates La Niña conditions while the opposite is true for ONI and MEI).

I then examined the data over the past 45 years, and split the average annual ENSO index in three, defining the 15 years having the largest La Niña influence as “La Niña years”, the 15 years having the largest El Niño influence as “El Niño years”, and the 15 years in the middle as “Neutral years”. In this analysis I assumed a 4-month lag between changes in ENSO and changes in global surface temperature, consistent with the results in Foster & Rahmstorf (2011).

In essence, I’m simply grouping the years whose temperatures had the most (in the uppermost 33%) La Niña/El Niño influence over the past 45 years, and seeing what those groupings tell us. I excluded years which were strongly influenced by the El Chichón (1983–1985) and Mount Pinatubo (1992–1994) volcanic eruptions (because large eruptions release particulates into the atmosphere which cause a strong short-term cooling), and looked at the temperature trends in each of the three categories (Figure 1).

Dana Nuccitelli assumes there were 15 El Niño, 15 La Niña and 15 ENSO-neutral years; that is, that they were split evenly. As a reference, according to NOAA’s definition, there were only 8 El Niño years since 1968. See Figure 2. Or to look at it another way, Dana assumes the threshold of the 15^th weakest El Niño will be comparable to that of the 15^th weakest La Niña. Let’s see if it is.

Figure 2

I’ve assumed that Nuccitelli inverted the Southern Oscillation Index (SOI) data to account for its inverse relationship with the other two datasets, and I’ve assumed that the “4-month lag” means he redefined a year so that it starts in September and ends in August. Also, assuming he averaged the three ENSO indices, Dana would have had to standardize them, because the Multivariate ENSO Index (MEI data here), Oceanic NINO Index (link includes ONI data), and Southern Oscillation Index (BOM SOI data here) all represent different variables with different scales.

So to replicate Dana Nuccitelli’s Average ENSO Index (what I’ll call the “Nuccitelli ENSO Index”), Figure 3 in monthly form, I inverted the SOI data, standardized all three indices, then averaged them. Figure 4 shows the Nuccitelli ENSO Index in annual form, with years lasting from September to August. The year from September 1967 to August 1968 is listed as 1968, and so on. Note the 1976 Pacific Climate shift in Figure 3. It stands out like a sore thumb. Also note the decay in the strengths of El Niño events from 1982 to present in Figure 4, which seems to have accelerated a little since the early 2000s. Why didn’t Nuccitelli illustrate and discuss his newly created ENSO index?

Figure 3

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Figure 4

Using the methods employed by Nuccitelli, I’ve identified the 15 strongest positive anomalies and classified them as El Niños in Figure 5, and I’ve done the same with La Niñas. According to the Nuccitelli ENSO Index, the threshold for El Niños is +0.45, while the threshold for La Niñas is -0.32. The Nuccitelli ENSO Index makes it easier to qualify as a La Niña than El Niño. What nonsense!! Another was way to look at it, the Nuccitelli index shows that ENSO was skewed toward El Niño conditions during the period he chose to examine. Why didn’t Nuccitelli present that at SkepticalScience?

Figure 5

If Dana had made +/- 0.45 the thresholds, then 2009 and 2012 would not have qualified as La Niña years and there’d be no reason for his post. On the other hand, if he used the thresholds of +/- 0.32, then 4 additional years would qualify as El Niño years: 1978, 1982, 2004 and 2010.

Then he and his fans at SkepticalScience would have been forced to ponder why ENSO is skewed toward a greater number of El Niño events. They’d likely blame it on human-induced global warming. To counter those assumptions, the abstract of Ray and Giese (2012) Historical changes in El Niño and La Niña characteristics in an ocean reanalysis ends with:

Overall, there is no evidence that there are changes in the strength, frequency, duration, location or direction of propagation of El Niño and La Niña anomalies caused by global warming during the period from 1871 to 2008.

ISOLATING EL NIÑO, LA NIÑA AND ENSO-NEUTRAL YEARS

Just for fun, let’s plot the annual NCDC global land plus sea surface temperature anomalies, for the Nuccitelli-defined years of 1968 to 2012, looking at El Niño, La Niña and ENSO-neutral years where each event type is isolated. We’ll present them using the breakdowns as defined by Nuccitelli and by NOAA. And we’ll exclude volcano years to be consistent with Nuccitelli’s presentation.

ENSO NEUTRAL YEARS

Figure 6 shows the ENSO-neutral years as defined by NOAA. The global surface temperatures during NOAA-defined ENSO-neutral years appear to rise pretty much continuously. On the other hand, the rate at which global surface temperatures warmed as Dana Nuccitelli defined them appear to slow drastically in recent years, Figure 7.

Figure 6

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Figure 7

EL NIÑO YEARS

The El Niño years are isolated in Figures 8 and 9. Using the El Niño years as defined by Nuccitelli, Figure 8, it could be argued that the warming rate of global surface temperatures slowed in recent years but it’s for a short time period, but with the NOAA method, the warming rate of El Niño years have definitely slowed, Figure 9.

Figure 8

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Figure 9

LA NIÑA YEARS

The recent slowing in the rate of warming shows up quite well when the La Niña years are broken out, regardless of whether we use the Nuccitelli method (Figure 10) or the NOAA method (Figure 11).

Figure 10

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Figure 11

I don’t think Dana Nuccitelli thought through his attempts to segregate ENSO phases. For fun, someone was bound to do what I did—eventually.

ADDITIONAL MISDIRECTION

In his post, Dana Nuccitelli states:

It’s also interesting to note that four of the past five years qualify as La Niña years in my methodology – they are in the top 33% of the strongest La Niña-influenced years since 1968. There has not been a similar El Niño year since 2005.

The year 2010 had a positive “Nuccitelli ENSO Index” value of +0.38, while 2009 and 2012 had negative values of -0.32 and -0.36 respectively. Refer to Table 1.

Table 1

I believe Dana needs to look at his data again. Makes one wonder why he misled his followers. That portion of his post had little impact and all he did with it was allow the data to show that he was wrong—then again, he didn’t post the data.

DANA NUCCITELLI MISREPRESENTS THE IMPACTS OF ENSO ON GLOBAL SURFACE TEMPERATURES

The intent of Dana Nuccitelli’s meaningless exercise is summed up in the closing sentence of his post. He writes:

But when we break the data into La Niña/El Niño/Neutral categories, or when we filter out their effects as Kevin C did, we see that the underlying global surface warming trend of approximately 0.16°C per decade remains beneath the short-term noise.

In other words, according to Dana Nuccitelli, ENSO is only short-term noise on a human-induced global warming signal. That’s nonsense, of course.

For four years, I’ve been illustrating the long-term effects of El Niño and La Niña events on satellite-era sea surface temperatures–that is, that El Niño and La Niña events are primarily responsible for the warming of global sea surface temperatures over the past 31 years. And I’ve been showing for about 3 ½ years how ocean heat content data indicates that Mother Nature is responsible for its warming. I won’t weigh down this post with that discussion again. But if the discussion is new to you, refer to my illustrated essay “The Manmade Global Warming Challenge” (42MB), introduced in my post here. And for a more detailed discussion, refer to my ebook Who Turned on the Heat?, which is for sale here in .pdf form for US$8.00.

The proponents of anthropogenic global warming over at SkepticalScience appear to find climate models to be more credible than data in discussions of global warming. So for them, I’ll provide a reminder of the Karnauskas et al (2012) paper A Pacific Centennial Oscillation Predicted by Coupled GCMs. I posted about that paper in the blog post here, and it was cross posted at WattsUpWithThat here.

The Abstract reads (my boldface):

Internal climate variability at the centennial time scale is investigated using long control integrations from three state-of-the-art global coupled general circulation models. In the absence of external forcing, all three models produce centennial variability in the mean zonal sea surface temperature (SST) and sea level pressure (SLP) gradients in the equatorial Pacific with counterparts in the extratropics. The centennial pattern in the tropical Pacific is dissimilar to that of the interannual El Niño–Southern Oscillation (ENSO), in that the most prominent expression in temperature is found beneath the surface of the western Pacific warm pool. Some global repercussions nevertheless are analogous, such as a hemispherically symmetric atmospheric wave pattern of alternating highs and lows. Centennial variability in western equatorial Pacific SST is a result of the strong asymmetry of interannual ocean heat content anomalies, while the eastern equatorial Pacific exhibits a lagged, Bjerknes-like response to temperature and convection in the west. The extratropical counterpart is shown to be a flux-driven response to the hemispherically symmetric circulation anomalies emanating from the tropical Pacific.

Significant centennial-length trends in the zonal SST and SLP gradients rivaling those estimated from observations and model simulations forced with increasing CO₂ appear to be inherent features of the internal climate dynamics simulated by all three models. Unforced variability and trends on the centennial time scale therefore need to be addressed in estimated uncertainties, beyond more traditional signal-to-noise estimates that do not account for natural variability on the centennial time scale.

On page 17 of 19 in pdf edition of Karnauskas et al (2012), the Summary and Concluding Remarks includes (my boldface):

1) If nature exhibits such strong natural variability of tropical Pacific SSTs on centennial time scales, then assumptions that the observed trend over the past century to a century and a half is a response to radiative forcing are tenuous. It could in fact be that the observed trend over the past century and a half is merely reflective of internal variability. If so, it could strengthen or weaken in the future as the natural variability evolves. This will combine with, and potentially interact with, any forced response and thus have implications for tropical Pacific and global climate.

2) If the centennial variability in the models is spurious, then it nevertheless is a robust component of the three analyzed models, is likely to exist in other models, and therefore will continue to influence coupled GCM projections of future climate, as well as initialized decadal hindcasts and forecasts conducted with GCMs. In all cases, it must be known at what stage the natural centennial variability exists at the beginning of a forecast or projection to isolate the forced change from the modeled internal variability.

Ocean heat content data and satellite-era sea surface temperature data both confirm the warming of the global oceans occurred naturally.

Thanks to blogger cohenite for reminding me about Karnauskas et al (2012).

ON FOSTER AND RAHMSTORF (2011)

Assumedly, to add credibility to his post, Dana Nuccitelli referred to the Foster and Rahmsorf (2011) paper “Global Temperature Evolution 1979–2010”. It too misrepresents the processes of El Niño and La Niña events. The blatantly obvious failings of Foster and Rahmsorf (2011) were illustrated and discussed in the post Revised Post – On Foster and Rahmstorf (2011).

CLOSING

In order to mislead the true-blue believers of human-induced global warming at SkepticalScience about the impacts of ENSO on global surface temperatures, Dana Nuccitelli redefined El Niño, La Niña and ENSO-neutral years. He also assumed that the 45 years of his analysis were evenly divided among those three ENSO phases, so that there were 15 each El Niño, La Niña and ENSO-neutral years. Replicating his results showed how his assumptions were flawed, because his new definition indicated that his newly defined ENSO index was skewed toward El Niño events during those 45 years.

And we discussed (previewed) how Dana Nuccitelli’s animated graph (Figure 1) was solely intended to misrepresent the long-term impacts of ENSO on the global surface temperature record. Then again, that’s nothing new for authors of posts at SkepticalScience.