Notes on ocean “warming”

I don’t have much time for research or writing these days, more’s the pity. So I must make do with snippets when they’re available. My favourite oceanographer made a few comments the other day on the ocean “heating” being discussed in the blogosphere. I’d like to pass them on.

He made some interesting and helpful remarks for the benefit of those of us not intimately acquainted with oceanography. However, to quieten the discussion which was threatening to get out of control he said pointedly, “I don’t have time to waste on Skeptical Science distortions.” We must hope that doesn’t make John Cook feel too inadequate.

Anyway, this is what he had to say about warming between 700–2000 m in the oceans.

1. The data below 700 m is very sparse — even with the increase in ocean drifters such as Argo. Therefore, the extremely small change in temperature associated with the very small heat content change is not reliable.

2. The main thermocline in the oceans lies between 500 and 1500 m on average depending on latitude. This is where the steepest gradient in temperature occurs in the bulk of the ocean. Note that I said on average. The position of the thermocline does vary over time. Best known example is the changes associated with ENSO — La Nina, thermocline depressed; El Nino, thermocline rises across the equatorial Pacific. There is evidence of shifts associated with the PDO. Doesn’t take much of a shift to account for an apparent global change in the 700–2000 m depth as low latitudes have higher sampling density than high latitudes — a change in the frequency of El Nino and La Nina events could do it.

3. Warm water doesn’t need to sink vertically to reach depth when dealing with intermediate waters (those around the thermocline). It is easier to move sideways along a density boundary than down through it. The main density boundary (pycnocline) is associated with the steepest temperature gradient (thermocline). It is not a flat surface — it is bowl-shaped; shallower at high latitudes and equator, and deepest around the tropics. Water at high latitudes sinks (subducts) by sliding sideways along the pycnocline. So warming of the Southern Ocean and Bering Sea eventually appears at 700–2000 m depth in the Central Pacific. Two little things though (1) the warming is solar driven and (2) it takes time to move (we think the shallowest parts may be of the order 50–70 years = PDO, and the deeper parts 100–500 y). So it is most likely a reflection of solar heating decades to centuries ago.

This is all basic stuff we teach in the introductory oceanography course — we don’t tend to get many atmospheric chemists attending.

So it’s no surprise they don’t understand this stuff.

I would emphasise the general unreliability of ocean temperatures. We don’t know enough about them to make a case for anything much. Also the amazingly long periods required for energy to move through the oceans.

129 Thoughts on “Notes on ocean “warming”

  1. Richard C (NZ) on March 28, 2013 at 10:01 am said:

    Update.

    >”0-2000m peaked 1Q2012″

    Not saying it wont go higher, in fact I think it already has. Just that with upper Pacific/Atlantic cooling there’s not much reason for below 700 to go much higher. Both upper and lower OHC metrics are being skewed by the Indian Ocean anyway.

  2. Richard C (NZ) on March 28, 2013 at 10:14 am said:

    >”Both upper and lower OHC metrics are being skewed by the Indian Ocean anyway”

    Not quite right again, should be:-

    “The 0-2000m OHC metric is being skewed by the Indian Ocean anyway (70% of the gain is in the upper Indian over the last 7 yrs).”

  3. TSI stopped increasing in 1980 but OHC continued to accelerate. If OHC lags TSI by 6-20 years as you suggest we would have expected to see OHC level off in 2000, why has this not happened?

  4. Richard C (NZ) on March 28, 2013 at 11:51 am said:

    >”TSI stopped increasing in 1980″

    Only in PMOD, see the ACRIM/PMOD/IRMB comparison here:-

    https://www.climateconversation.org.nz/2013/03/notes-on-ocean-warming/#comment-183636

    And clearly the level after 1986 was still at basically the same elevated level in all the composites. That’s where the analogy of boiling a pot of water comes in, all you do is turn it up full for a while and the water gradually gains heat. Even if you turn it down slightly (PMOD), the water will continue to gain heat.

    >”If OHC lags TSI by 6-20 years as you suggest we would have expected to see OHC level off in 2000, why has this not happened?”

    It has happened in the upper Pacific and Atlantic and more than just leveling off, both have cooled in the ARGO era (since 2003) consistent with thermal lag. Even the global aggregate stalled 2004:-

    http://oceans.pmel.noaa.gov/images/OHCA_curve_2012.png

  5. Richard C (NZ) on March 28, 2013 at 12:06 pm said:

    >”TSI stopped increasing in 1980″

    The peak is 1986 in PMOD, not 1980.

    >”…consistent with thermal lag [from peak input levels].”

  6. Richard C (NZ) on March 28, 2013 at 12:15 pm said:

    >”OHC lags TSI by 6-20 years”

    The “6” comes from an Atlantic study. Abdussamatov calculates 14 yrs +/- 6 (8 – 20), Scafetta approx 12 yrs from memory.

  7. Hi Richard C,
    If there is a 6-20 year lag then you would expect the output (temperature) to stabilise 8-20 years after the initial forcing (TSI) stabilised. The same will happen with your pot of water. If you turn up the heat the water will increase in temperature for a while but then stabilise.

    This is not what happened. TSI stabilised in the 80s relative to the sharp rise that preceded it yet total (0-2000m) OHC continued to rise post 2000. It doesn’t matter if there is local cooling, it is the net energy of the system that matters and this clearly continues to increase into at least 2012.

  8. Richard C (NZ) on March 28, 2013 at 1:09 pm said:

    >”…total (0-2000m) OHC continued to rise post 2000″

    What you are seeing is largely the Indian Ocean (82% last 7 yrs). And as I pointed out before, the elevated solar level didn’t just go away, it’s just that the “acceleration” of total gain is now over i.e. OHC is stabilizing consistent with maximum enthalpy being attained at the end of the modern solar Grand Max 1920 – 2012.

    >”It doesn’t matter if there is local cooling”

    The upper Pacific and Atlantic is “local” cooling Nick? Get real.

    >”it is the net energy of the system that matters and this clearly continues to increase into at least 2012″

    But not for much longer now that max TSI has plummeted 2013. that will be the test of time over the next year or two. I wont be surprised if there’s some more increase but it wont be continued “acceleration” that’s for sure considering upper ocean OHC is at standstill (also in the Indian now).

    Last 4 yrs 0-2000m World:-

    2009-3,12.811517
    2009-6,12.374052
    2009-9,13.947054
    2009-12,15.183682
    2010-3,16.048752
    2010-6,13.671132
    2010-9,14.129639
    2010-12,15.070600
    2011-3,15.453777
    2011-6,14.812579
    2011-9,17.095699 <<<<<<<<<< near peak
    2011-12,14.983609
    2012-3,17.434353 <<<<<<<<<< most recent peak
    2012-6,15.622717
    2012-9,15.494756
    2012-12,16.831072 <<<<<<<<< near peak

    BTW Nick, why hasn't GHG forcing heated the upper Pacific and Atlantic over the last 9 years (actually cooled progressively over that time) but it has (as I assume you assert) heated below 700m in both oceans?

    How does that work?

  9. Richard C (NZ) on March 29, 2013 at 10:38 am said:

    Looks like the CO2 feedback effect against falling solar has already begun (Magoo I hope you see this).

    James Hansen, Pushker Kharecha and Makiko Sato (2013)

    “…the huge post-2000 increase of uptake by the carbon sinks implied by figure 3”

    “…the large increase of carbon uptake by the combined terrestrial and ocean carbon sinks”

    http://hockeyschtick.blogspot.co.nz/2013/03/hansens-mea-culpa-says-man-made-global.html

    Hansen attributes it to coal use of course.

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