This is odd. WUWT for a change is welcoming a climate science paper published in Science, no less. After reading the comments I've figured out why. It's because the study finds something different to modeled paleoclimate. Deniers really dislike models of any kind. Well, actually the only models they don't like are climate models. And medium term weather models.
Shellfish tell the tale of ENSO
The paper describes research into ENSO using middens, which sounds like a novel way to explore past climate influences. Specifically, they were able to get monthly records of δ18O values in fossil Mesodesma donacium shells (a shellfish) on the coast of Peru. These mollusks have been eaten by fisher folk on the coast of Peru for more than 10,000 years. Imagine that! The shells are piled up in mounds up to 10 metres high. The very dry conditions meant that they were preserved very well.
What the international team of researchers found was that over the past 10,000 years, ENSO didn't behave as expected.
ScienceDaily.com has a press release about the paper. It has answered a few questions that I have about ENSO too. I've previously tried (not very hard) to find out what ENSO was like in the past. How long it's been a feature. I didn't have much luck and deferred the investigation.
It turns out that what has been assumed until now was that ENSO is strongly affected by insolation, which changes as the Earth changes its orientation to the sun over time, in a cyclic pattern. Because of this, it was previously thought that ENSO was weak to non-existent 6,000 to 8,000 years ago. Now it is still the case that insolation is one of the main forces, however what the scientists found was that insolation hasn't been the only thing affecting ENSO over the past several thousand years. The modern pattern of ENSO has been going for around 3-4.5 thousand years. There was a lull for a time, around four to five thousand years ago. In the early Holocene it was close to the modern ENSO. From the paper:
A central question in climate science is the extent to which changes in the climatic mean state influence ENSO variability. Long unforced climate simulations exhibit multidecadal internally-generated changes in ENSO behavior (30). Our data indicate that changes in the character of ENSO during the Holocene persisted for centuries, exceeding the time scale of model-generated internal variability. We therefore surmise that ENSO is sensitive to external forcing.
Climate models forced by 6 ka and 9.5 ka insolation produce a cooling and reduced ΔT in the eastern Pacific, along with reduced ENSO variance (3, 4). The simulated impact of insolation is consistent with the mean annual and seasonal range of SST derived from Peru mollusks, but not for ENSO variance, which the mollusks indicate was high in the early Holocene.
Climate simulations have demonstrated that a freshwater flux into the North Atlantic could offset the impact of insolation on ENSO in the early Holocene (31). Our data support this scenario and imply that any tendency toward lower ENSO variance during the mid-Holocene insolation regime may have been counteracted 6.7-10 ka by the influence of melting ice-sheets (31). While the low ENSO activity 4-5 ka is consistent with precessional forcing, the shift of ENSO asymmetry 6.7-7.5 ka points to factors within the climate system influencing changes in the spatial pattern of ENSO.
In other words, it wasn't just changes in insolation that affected ENSO variance. The researchers suggest that melting ice sheets may also have had a strong effect. Another thing from the paper is that recent ENSO variability these past few decades is greater than any other time in the Holocene, according to this study. The paper states:
Mean annual SST was significantly lower than today 4.5-9.6 ka, especially in southern Peru, where SSTs were ~3°C cooler (Fig. 2A). These cooler conditions imply an increase in the intensity of coastal upwelling (13, 14). Although highly variable, the seasonal range of SST (ΔT) was significantly reduced compared to the late 20th century during most of the Holocene, with reductions up to ~30% (equivalent to ~1.1°C) 0.5, 4.7, 8.5 and 9.5 ka (Fig. 2B).
Furthermore, ENSO variability, as derived from the variance of ΔT, was higher in the late 20th century than at any other sampled interval of the Holocene, even excluding the influence of the 1982-83 and 1997-98 extreme El Niño events (Fig. 3A). The lowest ENSO variance in the eastern tropical Pacific occurred at ~4.7ka (55% reduction, 82% confidence level) (Fig. 3A).
Additional info.Here is Figure 2 from the paper, which shows the mean annual sea surface temperatures at particular times as derived from their analysis, and the estimated range of sea surface temperatures.
Fig. 2 Holocene reconstruction of mean annual SST and seasonal SST range from fossil mollusk δ18O values on the Peru coast.
- (A) Mean SST values obtained from individual shells (open diamonds). For each shell midden, the average SST was represented over the occupation timespan (thick horizontal line, prolonged by a thin line for the 1σ calibration interval). The standard error (±1σ) of reconstructed SSTs is represented by blue bars for the central coast and red bars for the southern coast of Peru (fig. S1). A second error bar (±1σ) incorporates any potential systematic error introduced by calibration of the mollusk δ18O SST proxy plus uncertainty in the correction for ice volume effects on ocean δ18O (8, 11). The level of confidence (LOC) that reconstructed values of mean annual SST are significantly different from modern SSTs (student t test) is indicated by black bars in the lower portion of both panels, with the dotted line indicating the 90% LOC.
- (B) Seasonal ranges of M. donacium shell δ18O normalized to the modern mean value. Individual shells record one to eight successive ΔT values (open diamonds) (8). For each shell midden, average values and standard errors were represented as in (A). The Horizontal dashed line represents modern conditions. LOC are indicated as in (A).
"We thought we understood what influences the El Niño mode of climate variation, and we've been able to show that we actually don't understand it very well," said Julian Sachs, a UW professor of oceanography.
The ancient shellfish feasts also upend a widely held interpretation of past climate. "Our data contradicts the hypothesis that El Niño activity was very reduced 10,000 years ago, and then slowly increased since then," said first author Matthieu Carré, who did the research as a UW postdoctoral researcher and now holds a faculty position at the University of Montpellier in France.
In 2007, while at the UW-based Joint Institute for the Study of the Atmosphere and Ocean, Carré accompanied archaeologists to seven sites in coastal Peru. Together they sampled 25-foot-tall piles of shells from Mesodesma donacium clams eaten and then discarded over centuries into piles that archaeologists call middens.
While in graduate school, Carré had developed a technique to analyze shell layers to get ocean temperatures, using carbon dating of charcoal from fires to get the year, and the ratio of oxygen isotopes in the growth layers to get the water temperatures as the shell was forming.
The shells provide 1- to 3-year-long records of monthly temperature of the Pacific Ocean along the coast of Peru. Combining layers of shells from each site gives water temperatures for intervals spanning 100 to 1,000 years during the past 10,000 years.
The new record shows that 10,000 years ago the El Niño cycles were strong, contradicting the current leading interpretations. Roughly 7,000 years ago the shells show a shift to the central Pacific of the most severe El Niño impacts, followed by a lull in the strength and occurrence of El Niño from about 6,000 to 4,000 years ago.
One possible explanation for the surprising finding of a strong El Niño 10,000 years ago was that some other factor was compensating for the dampening effect expected from cyclical changes in Earth's orbit around the sun during that period.
"The best candidate is the polar ice sheet, which was melting very fast in this period and may have increased El Niño activity by changing ocean currents," Carré said.
Around 6,000 years ago most of the ice age floes would have finished melting, so the effect of Earth's orbital geometry might have taken over then to cause the period of weak El Niños.
In previous studies, warm-water shells and evidence of flooding in Andean lakes had been interpreted as signs of a much weaker El Niño around 10,000 years ago.
The new data is more reliable, Carré said, for three reasons: the Peruvian coast is strongly affected by El Niño; the shells record ocean temperature, which is the most important parameter for the El Niño cycles; and the ability to record seasonal changes, the timescale at which El Niño can be observed.
"Climate models and a variety of datasets had concluded that El Niños were essentially nonexistent, did not occur, before 6,000 to 8,000 years ago," Sachs said. "Our results very clearly show that this is not the case, and suggest that current understanding of the El Niño system is incomplete."
What an informative study. Let's see how the rabble at WUWT liked it.
From the WUWT comments
I'm not sure that Bobby Davis understands the research (or science in general), because he says:
August 8, 2014 at 3:53 pm
Slowly but surely the truth is coming out about how untrustworthy the computer models used by climate scientist are, compared to real empirical data. CO2 alarmist’s are losing their minds over this & I take great enjoyment in watching them try to explain their point of view.
Theo Goodwin has had a change of heart about science. He usually bags it. This time he says:
August 8, 2014 at 3:54 pm
“Climate models and a variety of datasets had concluded that El Niños were essentially nonexistent, did not occur, before 6,000 to 8,000 years ago,” Sachs said. “Our results very clearly show that this is not the case, and suggest that current understanding of the El Niño system is incomplete.”
I just love real science.
sinewave is more cautious, because the study mentions that dreaded words "global warming". He/she says:
August 8, 2014 at 4:03 pm
First line in the abstract: “Understanding the response of the El Niño-Southern Oscillation (ENSO) to global warming requires quantitative data on ENSO under different climate regimes” They just had to say it. It’s probably a requirement to frame things relative to global warming to get published….
FergalR is wrong, as this study shows. He seems to be confusing medium term weather forecasts with climate projections when he says:
August 8, 2014 at 4:09 pm
I appreciate their hard work but nobody has ever had a clue about what causes changes in ENSO.
Every prediction of it they make more than 3 months out fails miserably yet they’re surprised computer models don’t know what it was like 10,000 years ago?
I don't know what sturgishooper is referring to when he/she says:
August 8, 2014 at 4:24 pm
How can there be global “climate changes” from one year to the next? Weather, yes. Climate, no. Even one decade to the next isn’t climate.
Jared picks up on the general mood at WUWT, but doesn't have a clue about climate science, and says:
August 8, 2014 at 4:59 pm
Are all these new studies coming out because a new generation has taken over and the corrupt ones like Hansen, Mann, Briffa, Jones are aging towards retirement? Will history look back and show that 25 year span starting in 1988 for what it was ‘A time when a group of scientists led by Hansen and Mann decided to distort and adjust facts to meet a political agenda’. Are hurricanes up? Are tornadoes up? Mosher and Stokes know deep down that CAGW is a myth and the slight warming we have gotten is mostly beneficial.
During the discussion, various commenters explained what they mean when they use the denier-specific acronym "CAGW". Not well, but a couple gave it a shot. It started when Steven Mosher says:
August 8, 2014 at 5:39 pm
Cagw isn’t even defined.
Bill_W says - and a mod chimes in:
August 8, 2014 at 6:00 pm
CAGW is clearly understood. AGW is warming of 0 degrees to 1.99 C. CAGW is 2.0 or higher. Life on earth will end if the temp. goes up 2C. Ebola most likely will kill all the humans before the plankton dying kills the rest of life on earth.
[It is very telling of today's headlines, and today's CAGW supporters, that we do not know (and cannot tell) if this paragraph needs a "/sarcasm" tag added. .mod]
August 8, 2014 at 6:19 pm
CAGW = Catastrophic Anthropogenic Global Warming.
That’s the definition.
Ian Bryce says, for no reason I can fathom:
August 8, 2014 at 8:22 pm
The Bible has many stories of droughts prior to 500BC. Some were as long as 3.5 years, and then there was the big drought in Joseph’s time which lasted 7 years, around about 1875BC.
Lewis P Buckingham says:
August 8, 2014 at 8:28 pm
How do we know that shells are a good proxy for temperature?
I recall the argument that tree rings were often a poor proxy for temperature because other things were relevant also to the growth of tree rings.
Such things as humidity, aridity of the soil and presence of nutrients, competition, shading and even CO2 concentration as well as the age and maturity of the tree.
Is there any way to check that this important sea shell proxy is valid?
TomRude shows off his ..ahem.. extensive knowledge of the subject and says:
August 8, 2014 at 10:18 pm
Mosher does not even know what an El Nino is meteorologically… It is a distortion of the boreal hemisphere circulation, so there are no reasons that this event would not have happened in the past, especially given the known climatic shifts (glaciations/deglaciations).
Don Easterbrook decides that ENSO reaches as far as his favourite ice sheet way up on the summit in central Greenland and says:
August 8, 2014 at 10:24 pm
Interesting results. Some years ago, I plotted up the raw oxygen isotope data measured by Stuiver and Grootes (1997) from the GISP2 ice core and was surprised to find 40 recurring warm/cool periods since 1480 AD. The average of each warm or cool cycle was 27 years, essentially the same as the PDO (http://www.nipccreport.org/reports/ccr2a/pdf/Chapter-5-Cryosphere.pdf
Figure 188.8.131.52, page 689. I’ll plot up the rest of the data and compare it with the data of Carre et al.
Mac the Knife is always very dismissive of anything sciency, but he likes this study and says:
August 8, 2014 at 10:36 pm
New data shows modern El Ninos are the same intensity/severity as they were 10,000 years ago… and the best ‘climate models’ don’t emulate this at all. The ‘climate models’ are shown to be significantly in error, yet again. GIGO.
Matthieu Carré, Julian P. Sachs, Sara Purca, Andrew J. Schauer, Pascale Braconnot, Rommel Angeles Falcón, Michèle Julien, Danièle Lavallée "Holocene history of ENSO variance and asymmetry in the eastern tropical Pacific." Science, 2014; DOI: 10.1126/science.1252220