Claim: The Warmest period in 600,000 years?


I found an article that leads the reader to believe that the Earth is currently warmer than it has been at any time in past 600,000 years.  The basis for that is a link to the Vostok ice core and a link to some general data sets.  The data they are referencing certainly doesn’t support that statement.  Here is what the Vostok ice core shows for the past 350,000 years.

The Inconvenient Skeptic

Vostok 350,000 Year Temperature Record

The current interglacial has the lowest temperature of the past three.  Some of them were shorter, but they were all warmer. The statement that we are warmer now than compared to the other interglacial periods is simply wrong.  That doesn’t even include the biggest of the interglacial periods which was finishing up 400,000 years ago.  It is normally called the Hoxnian Interglacial.  The Vostok ice core does not fully cover that one so I will leave that for another day.  To say that the Earth is warmer now than the Hoxnian is absurd.

As for the Holocene Interglacial.  I still haven’t put together the new article on the new chart, but I will get to that soon.  Since I did have the Vostok data up I put together a quick 12,000 year chart of the Vostok ice core.

The Inconvenient Skeptic

12,000 Year Vostok Ice Core

This is the raw data (with moving average).  By the nature of the Vostok ice core, each data point represents about 20 years of temperature data (by isotope proxy).  To me it appears that there is some very natural variation in the data.  For the past 10,000 years the standard deviation of the data is 0.67 °C. As there is no real trend in the data over the last 10,000 year period that seems like a reasonable value.  The average temperature for the same period is -0.37 °C. So anything within the window of -0.37 +/- 1.34 °C is within two standard deviations of the normal temperature for the past 10,000 years.

Since the average temperature from 1990-2010 is 0.26 °C, that means the average is well within a single standard deviation when compared to the natural variability of the Vostok ice core data for the past 10,000 years.  Where does that leave the statement that we are warmer than anytime within the past 600,000 years?   I will leave that for you to decide.

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Posted in Fear and Misinformation by inconvenientskeptic on October 29th, 2010 at 4:00 am.

9 comments

This post has 9 comments

  1. Glenn Tamblyn Oct 30th 2010

    John

    One of the defining characteristics of what I might call the ‘dark side’ of climate change scepticism is cherry picking, misquoting and using things out of context to make a false point. I hope you aren’t doing that here.

    The actual quote from SkS is “Secondly, if we cause a ~2 °C warming, some scientists think feedbacks such as melting permafrost releasing more greenhouse gases might kick in. Ice and sediment cores suggest we haven’t been this warm in at least 600,000 years so we’re not sure – but this could trigger a lot more warming.”

    This quote is NOT suggesting we are 2 Deg warmer now and that current temps are higher than in the last 600KY.

    It is saying that IF we do see a 2 Deg warming in the future that could cause various unpleasant feedbacks and that such a warming would be unprecedented in the Ice Core Record. Not that todays Temps are as your post seems to imply that they said.

    You have shown a graph of the Vostok core as an anomaly, but not shown what the baseline for the anomaly is. Is the modern era the baseline? I dunno, you haven’t spelled this out.

    Then you do an anlysis based on 1990 – 2010 but it is unclear whether you are referring to anomaly change over that period, or the average value of the anomaly. You need to be far more exact in your use of language or you could mislead people.

    And why only from 1990? Warming started earlier than that.

  2. inconvenientskeptic Oct 30th 2010

    Glenn,

    Two points. First it does read very much in the manner I described. Others have commented that it reads that way, but last I check it had not been corrected.

    Second, as I stated when describing the Vostok data, each point represents ~20 years of temperature. Since the the most recent 20 year period (which is claimed to be the warmest) it is an accurate representation and not cherry picking at all.

    Comparing single year data in a noisy set to a data set of 20 year averages will always cause overstatement in the single year set. So by choosing the most recent 20 year period I was actually being precise in my comparison.

    I even included the warm, but incomplete 2010 to help boost the average.

    Aside from those items, it is also clear that a 2 °C increase would not be the warmest in the last 600,000 years. A sustained 2 °C increase for more than 20 years would have a shot at the warmest 20 year period in the Holocene, but would still be cooler than the Eemian and much cooler than the Hoxnian.

    So the 600,000 year claim is inaccurate on the time scale, even if it was clearly phrased for after a 2 °C increase.

    The article is incorrect and misleading and I pointed that out.

  3. Glenn Tamblyn Oct 31st 2010

    You haven’t answered my question about what the baseline is for the Vostok core.

  4. Glenn,

    John has beyond demonstrated a baseline.

    The data says we are in “Zone One High”, no adjustment needed to the process as of yet. Nature appears to be well within it’s “Process Capability Index”. No worries. We do need a little metrology improvements (record keeping, change control, gauge SPC).

    Nice article John 😉

  5. inconvenientskeptic Oct 31st 2010

    As Intrepid stated the baseline is stated for the past 10,000 years.

    There is no “baseline” anomaly over periods of 400,000 years. There is a massive window of approx -3 +/- 7 °C. That is meaningless in regards to the current situation.

    Statistically we are well within the norm for that past 10,000 years based on the Vostok ice core. The 3 sigma point for the past 10,000 years is 2 °C which is the limit of the process window.

  6. drewski Nov 4th 2010

    Glenn is right. The passage regarding IF we were to warm ~2C is clearly and simply written — you built an entire rebuttal argument based on a fabrication.

    I would categorize you as a SCEPTIC = So Called Experts Perpetually Talking in Circles.

    As opposed to a SKEPTIC = part of the scientific method — examination and questioning by a person with experience or training in the field under discussion.

  7. inconvenientskeptic Nov 4th 2010

    Drew,

    We try to avoid personal insults to zero. I also clearly point out that even a 2C increase would also be inaccurate, even on a 10,000 year timescale much less a 600,000 year timescale.

    As the most recent article shows, the Holocene has been cooling for thousands of years.

    Again, please keep insults down. Further comments that contain them will not be approved.

  8. drewski Nov 4th 2010

    I say again, you based your argument on something that was clearly not stated. You: “I found an article that leads the reader to believe that the Earth is CURRENTLY WARMER than it has been at any time in past 600,000 years. . . . . ”

    Actual: “Ice and sediment cores suggest global temperatures HAVEN’T BEEN ~2 °C HIGHER than today in 600,000 years so we’re not sure – but this could trigger a lot more warming.”

    Everything in your argument from that point on is just noise.

  9. richatd verney Jan 10th 2011

    Glenn and John

    I have not read the SkS article to which Glenn refers but I have read his quote. The quoted passage is very poorly written. Accordingly, it is not surprising that it is open to various interpretations. What is clear is that the phrase “…we haven’t been this warm in at least 600,000 years…” is written in the present tense thereby denoting something that is happening now. If the phrase was intended to refer to something that might transpire in the future (with assumed feedbacks etc), then the phrase should have been written in the future conditional tense (which it has not been). It should have read along the lines ‘,,,we will not have been so warm in at least 600,000 years….”
    I think that it is somewhay unfair to suggest that John may be cherry picking given that he was responding to a poorly written statement which in itself is inherently contradictory.

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