Another “hockey stick” graph spurs more climate hype

Last week there was much buzz in the media about a new paper that used fossils from sediment and ice cores to reconstruct global temperatures for the last 11,000 years.

Typical of the headlines was this one from the Arizona Daily Star: “Study: Global heat spike unique in past 11,000 yrs.” The fuss was caused by this paper: “A Reconstruction of Regional and Global Temperature for the Past 11,300 Years” by Marcott et al., published in Science.

The paper’s graph causing all the stir is shown below:

Marcott-graph1The paper’s abstract contains this sentence: “Current global temperatures of the past decade have not yet exceeded peak interglacial values but are warmer than during ~75% of the Holocene temperature history.” That alone gives the lie to the graph and to the Star’s headline.

A critique of the paper may be found at WUWT here.

Essentially Marcott et al. used Michael Mann’s hockey stick trick to co-join two data sets of very different resolutions to come up with the spike, in other words they joined apples and oranges.

That procedure blurs out the Medieval Warm Period of about 1,000 years ago even though that period was as warm or warmer than current temperatures.

In the WUWT critiques, Robert Rhode, of the Berkeley Earth Surface Temperature Study, explains the problem:

“They rely on proxy data that is widely spaced in time (median sampling interval 120 years) and in many cases may also be subject to significant dating uncertainty. These effects will both tend to blur and obscure high frequency variability. They estimate…that only 50% of the variance is preserved at 1,000-year periods. This amount of variance suppression is roughly what you would expect if the underlying annual temperature time series had been smoothed with a 400-year moving average. In essence, their reconstruction appears to tell us about past changes in climate with a resolution of about 400 years. That is more than adequate for gathering insights about millennial scale changes during the last 10,000 years, but it will completely obscure any rapid fluctuations having durations less than a few hundred years… should be careful in comparing recent decades to early parts of their reconstruction, as one can easily fall into the trap of comparing a single year or decade to what is essentially an average of centuries….since their methodology suppresses most of the high frequency variability, one needs to be cautious when making comparisons between their reconstruction and relatively rapid events like the global warming of the last century.”

Another point from geologist Dr. Don Easterbrook:

“Eighty percent of the source data sites were marine, so temperatures from 80% of the data set used in this paper record ocean water temperatures, not atmospheric temperatures. Thus, they may reflect temperature changes from ocean upwelling, changes in ocean currents, or any one of a number of ocean variations not related to atmospheric climates. This in itself means that the Marcott et al. temperatures are not a reliable measure of changing atmospheric climate.”

Additional comments from Dr. Judith Curry, Georgia Tech: “There doesn’t seem to be anything really new here in terms of our understanding of the Holocene.  Mike’s Nature trick seems to be now a standard practice in paleo reconstructions.  I personally don’t see how this analysis says anything convincing about climate variability on the time scale of a century.”

Interestingly, buried in the supplementary material to their paper, Marcott et al. showed the results of running their data through a computer program which used different algorithms and assumptions. This exercise produced a quite different graph from the same data:


That graph is not nearly as scary looking as the one touted in the headlines. This just goes to show that the results depend on the assumptions and methods used in the computer program: Garbage in – Garbage out. Of course, that graph would not garner headlines.


WUWT update post: Marcott et al claim of ‘unprecedented’ warming compared to GISP ice core data.  This update from WUWT graphically shows that the current warmth is not unprecedented as claimed.  The first sentence of Marcott et al. says, “Surface temperature reconstructions of the past 1500 years suggest that recent warming is unprecedented in that time.”  This is clearly false.  Anthony Watts superimposes the Marcott data over an earlier study of Greenland ice core data  to get this graph:


 To put things in perspective, look at the following graph, a temperature reconstruction based on ice core data.  Unlike the Marcott paper, this reconstruction shows that current temperatures are among the coolest of the last 10,000 years.  Notice also the previous periods of rapid warming (red lines on the graph).

Cuffey and Clow

UPDATE: April 2, 2013, Ross McKitrick explains how Marcott purposely changed the dates on proxy core to produce the uptick:

UPDATE: A simple test shows where Marcott goes wrong see here.  See a good explanation of the deception from Resilient Earth here.

Steve McIntyre deconstructs Marcott:

Marcott Mystery #1

No Uptick in Marcott Thesis

Marcott’s Zonal Reconstructions

How Marcottian Upticks Arise

The Marcott-Shakun Dating Service

Hiding the Decline: MD01-2421

See also:

20th Century temperatures explained as natural recovery from Little Ice Age

More evidence that current warming is not unusual


    1. The earth warms and cools. Right now the physical evidence shows that earth has not warmed for at least 16 years in spite of increasing CO2.

      1. What physical evidence?
        If you look at Earth’s primary heat sink, the oceans. You see a steady warming trend.

      2. Why would you use the surface temperature, which is highly variable and influenced primarily by up and down welling, when you have temperature measurements of the ocean itself?

    2. Again, you are deflecting the issue which is not the incidence of warming or cooling, but the major cause of the temperature cycles. There is no physical evidence that our carbon dioxide emissions play a major role.

      1. That is still not evidence that GHGs are the major cause of warming. The Earth compensates, always has.

    3. For the two commenters Eric Vitiello & sdavis3398, see my first comment at the top on “Thanks for the link to Al Gore’s Reality Drop effort…”

      You guys are incapable of coming up with material on your own? Despite RealityDrop’s Feb 28 Tweet about their announcement of their “new” effort to dispel misinformation, I said this about their efforts back on Nov 17 2012:

  1. You know it’s funny that virtually all top climate scientists would disagree with you. No one denies that the Earth’s climate has changed throughout time (although plenty would disagree with your graphs), but the science is settled on man-made climate change: we are clearly the driving force in warming our planet now, it isn’t natural, and it’s very rapid and dangerous. Get your head out of the sand.

    1. Anyone who claims science is settled doesn’t understand science. But since you claim that humans “are clearly the driving force in warming our planet” perhaps you could present some physical evidence to support that claim. Also, your first sentence is not true.

      1. Jonathan… to be fair… like ALL science… NONE of it is ever “settled”

        Brian’s first sentence, “virtually all” means 97-98% of CLIMATE scientists in the most recent poll. A lot of their work is posted here>

        A survey of 3146 earth scientists asked the question “Do you think human activity is a significant contributing factor in changing mean global temperatures?” (Doran 2009). More than 90% of participants had Ph.D.s, and 7% had master’s degrees. Overall, 82% of the scientists answered yes. However, what are most interesting are responses compared to the level of expertise in climate science. Of scientists who were non-climatologists and didn’t publish research, 77% answered yes. In contrast, 97.5% of climatologists who actively publish research on climate change responded yes. As the level of active research and specialization in climate science increases, so does agreement that humans are significantly changing global temperatures.

        In other words… The smarter the scientist (who specializes in climate science) the more likely they are to agree that human activity is a significant contributing factor in changing mean global temperatures.

        Maybe you should check to see what “physical evidence” they’re basing their opinions on.

      2. The 97%-98% consensus myth is based on the answers of just 75 scientists out of the 3,146 who responded to a poll. See my post on consensus in science:
        And, by the way SkepticalScience is a propaganda mill, not a reliable science source, see:

      3. Your group signed off on denying global warming back in 2007.


        See also: List of scientists opposing the mainstream scientific assessment of global warming

        As of 2007, when the American Association of Petroleum Geologists released a revised statement,[103] no scientific body of national or international standing rejected the findings of human-induced effects on climate change.[10][11]

      4. 2 questions for you Jonathan: 1. How many planets do we (as plausible homes for humanity) on which to run the experiment of doing nothing? 2. Is the science on the linkage between cigarettes and increased incidence of lung cancer settled?

        There is a saying known to younger people: “DNFTT” I didn’t know what that meant until recently. By responding to you, I am violating the advice in “DNFTT.” It means “Do Not Feed The Troll.’

      5. Commenter “sdavis3398” really needs some help. Trolls would be the people dropping into comment sections asking irrelevant questions about the number of planets to experiment on or about the cigarettes/lung cancer link, not the author of the actual article. It is I and he who are feeding the trolls since there is some entertainment in watching them fail to actually defend their AGW position. Perhaps a sadistic thing to do, but still somewhat entertaining, and potentially rewarding if it ever dawns on a troll that they rely on people to supply them with material that doesn’t stand the test of science.

        As I’ve said elsewhere, there are only two kinds of people on the planet: those who are skeptics of AGW and those who would become skeptics after objectively reading skeptic material.

  2. There is very strong evidence of warming. It is just convenient that a la Nina ended this period for the skeptics. If we end it on a El Nino there is a clear indicator of warming by the statistical method.

    Giss 1995 to

    Trend: 0.141
    ±0.149 °C/decade (2σ)

    Giss 1995 to

    Trend: 0.113
    ±0.113 °C/decade (2σ)

    1. The argument is really about the causes of temperature cycles, not the cycles themselves.

      1. The operative words in your link are “atmosphere-ocean climate modeling study” Just computer GIGO no physical evidence.

  3. There is no need for the hockey stick graph to know that the earth is warming; there is plenty of other evidence out there.
    You should look up the NOAA’s Mauna Loa data which shows a direct correlation between increasing carbon dioxide levels and temperature.

    1. Thanks for the link to Al Gore’s Reality Drop effort, which in case you haven’t noticed is one in which: A) Gore has so little confidence in your own ability to think for yourself that he feels obligated to provide talking points for you to copy & paste into comment sections like this, and, B) the effort was bombing so badly that Anthony Watts felt obligated to give it a ‘hockey stick’ of a readership bump

      But to your main point, skeptics are not doubting (or “denying, as your talking points marching orders like to put it) that we are experiencing global warming. What skeptics question is whether it is proved that human-induced greenhouse gases are the primary driver. It is that simple, and is why the “denier” label is imploding so badly for those who attempt to portray skeptics as such.

  4. Look at the PIOMAS arctic ice voumes which closely tally with cutting edge earth sat data. We have lost 75% og ice mass over the last 30 years…. Then look at northern hemisphere temperatures in the following link.

    1. Criticizing anyone in a demeaning way for linking to WUWT without offering a scintilla of evidence of what is incorrect, silly, misleading, disingenuous, or false about WUWT material is an indicator that the critic is unable or unwilling to participate in reasoned debate.

      Please, indulge us. Tell us precisely what is at fault in, say, the latest Marcott critique by a guest poster at WUWT:

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