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Oceans Were Warmer In MWP

April 24, 2015

By Paul Homewood


While we’re on the topic of sea surface temperatures, let’s take a look at this paper from 2013, that I don’t recall the BBC or Guardian reporting!





Observed increases in ocean heat content (OHC) and temperature are robust indicators of global warming during the past several decades. We used high-resolution proxy records from sediment cores to extend these observations in the Pacific 10,000 years beyond the instrumental record. We show that water masses linked to North Pacific and Antarctic intermediate waters were warmer by 2.1 ± 0.4°C and 1.5 ± 0.4°C, respectively, during the middle Holocene Thermal Maximum than over the past century. Both water masses were ~0.9°C warmer during the Medieval Warm period than during the Little Ice Age and ~0.65° warmer than in recent decades. Although documented changes in global surface temperatures during the Holocene and Common era are relatively small, the concomitant changes in OHC are large.

Editor’s Summary

Global warming is popularly viewed only as an atmospheric process, when, as shown by marine temperature records covering the last several decades, most heat uptake occurs in the ocean. How did subsurface ocean temperatures vary during past warm and cold intervals? Rosenthal et al. (p. 617) present a temperature record of western equatorial Pacific subsurface and intermediate water masses over the past 10,000 years that shows that heat content varied in step with both northern and southern high-latitude oceans. The findings support the view that the Holocene Thermal Maximum, the Medieval Warm Period, and the Little Ice Age were global events, and they provide a long-term perspective for evaluating the role of ocean heat content in various warming scenarios for the future.


This paper demolishes the idea that CO2 has been responsible for the warming of the seas since the Little Ice Age.

  1. Jim Franklin permalink
    April 24, 2015 7:35 pm

    Whilst the paper raises an interesting conundrum, and one that lends itself to the notion that global temperature changes have far more complex paths and causes than is currently reported, in and of itself it does not destroy the CO2 observations either.

    The full picture of global ocean heat production, storage and transfer to the atmosphere is very poorly understood so what this paper should generate is a huge desire to solve this massive hole is our understanding of the thermal budget of the planet.

  2. mkelly permalink
    April 24, 2015 8:03 pm

    That must be when this fellow started to grow.

    Old Tjikko is a 9,550-year-old Norway Spruce, located on Fulufjället Mountain of Dalarna province in Sweden.

  3. April 24, 2015 9:19 pm

    ‘This paper demolishes the idea that CO2 has been responsible for the warming of the seas since the Little Ice Age.’

    Hockeyshtick pretty much buried that argument in 2012.

  4. April 24, 2015 10:58 pm

    David A (not Appel) explain it with great metaphor here:

  5. April 25, 2015 5:37 am

    And the warmer oceans during the MWP and modern times are explained (> 99% significance) by the solar variations at these times…the “medieval and modern [solar] maxima.”

    Here we present an exceptionally well-dated marine sediment sequence in the eastern Norwegian Sea which records 1–2°C variations of temperature in northward flowing Atlantic waters that are robustly correlated with various estimates of solar activity spanning the last 1000 years. The temperature and solar proxy variations appear to be synchronous within dating errors, which, together with the large amplitude of the temperature signal and its correlation into central Europe, suggests strong coupling of the regional atmospheric and oceanic responses to the Sun.

    Lowest isotope values (highest temperatures) of the last millennium are seen ∼1100–1300 A.D., during the Medieval Climate Anomaly, and again after ∼1950 A.D. The largest and most sustained isotopic increases (coolings) are centered at ∼1500 A.D. and ∼1700 A.D., corresponding to the regional Little Ice Age. …

    The presence of medieval and 20th century warmth and Little Ice Age cooling in our records suggests a possible connection to known solar variations at these times (i.e., the Spører and Maunder minima and medieval and modern maxima, respectively).

    For the period after 1500 A.D., during which we have greatest confidence in the sediment age model, correlations with the various solar proxies range from ∣R∣ = 0.71 to 0.87 (all significant at >99%).

    On balance, the observed relationship of nSST [near sea surface temperatures] and solar proxies suggests a climate response to the Sun within the characteristic inertial timescale of the upper ocean, which is one to several decades. Recurrent, episodic volcanic forcing may also influence the ocean climate signal at this timescale, however, our results indicate that approximately 50–70% of the observed multidecadal to century-scale δ18O variation may be explained by solar forcing alone.

    • April 25, 2015 12:55 pm

      Thanks kenneth for that impressive study. Solar forcing of ocean SST is a controversial but promising arena.

      • emsnews permalink
        April 25, 2015 4:10 pm

        The sun causes warm cycles and lack of sufficient solar energy causes Ice Ages.

        The sun runs this entire hot/cold system and it went into an extreme hot/cold mode about 2 million years ago.

  6. April 25, 2015 12:53 pm

    the mechanism of CO2 induced global warming implies an increase in minimum temperatures, and /or chaos in my graph, but there just isn’t any..

  7. April 25, 2015 1:18 pm

    kennethrichards quotes:
    …….which is one to several decades.

    Henry says:
    it is a bit more than that, actually,

    the graph shown in my previous comment is half of the Gleissberg cycle

    I hope that soon we will begin the march back up again. (The sun is now at it hottest/whitest ever point in 87 years)

    • emsnews permalink
      April 25, 2015 4:12 pm

      Correct. My deceased father, Dr. Aden Meinel, one of the founders of the first solar observatory at Kitt Peak, called me before he died and he warned me that the sun would now enter a declining cycle rather than a warming cycle.

      Since I live in upstate NY, he thought I should be warned. And so far, it has definitely been getting cooler, not warmer, each year.

  8. April 25, 2015 4:21 pm

    He must be one of only a few people who figured it out. When the sun’s magnetic fields are declining, and it seems the sun is hotter/brighter, earth’s atmosphere acts like a defence shield and temperatures start declining:

  9. April 25, 2015 10:23 pm

    Thanks, Paul. It makes a lot of sense to track the temperature of the oceans, after they got so big, they dominated the lower troposphere temperatures, as they do today.

  10. meto permalink
    April 27, 2015 7:35 pm

    Paul. Thank you once again. I teach near the People’s Republic, an AGW “warminista” stronghold that ambushes their fellow Climate Scientists in the middle of the night. I want you to know that I have used your blog with my college students…all of whom have, or are developing, a healthy inquistive scientific perspective. To borrow from Prof. Judith Curry at Georgia Tech, we study the “unknown” to make it known by careful research.
    Nary a one of the students is a “warminista” Card Carrying member. There is hope. Thank you again for your tireless work!

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