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What ocean heating reveals about global warming

Filed under: — stefan @ 25 September 2013

The heat content of the oceans is growing and growing.  That means that the greenhouse effect has not taken a pause and the cold sun is not noticeably slowing global warming.

NOAA posts regularly updated measurements of the amount of heat stored in the bulk of the oceans.  For the upper 2000 m (deeper than that not much happens) it looks like this:

heat_content2000m

Change in the heat content in the upper 2000 m of the world’s oceans. Source: NOAA


The amount of heat stored in the oceans is one of the most important diagnostics for global warming, because about 90% of the additional heat is stored there (you can read more about this in the last IPCC report from 2007).  The atmosphere stores only about 2% because of its small heat capacity.  The surface (including the continental ice masses) can only absorb heat slowly because it is a poor heat conductor.  Thus, heat absorbed by the oceans accounts for almost all of the planet’s radiative imbalance.

If the oceans are warming up, this implies that the Earth must absorb more solar energy than it emits longwave radiation into space. This is the only possible heat source. That’s simply the first law of thermodynamics, conservation of energy. This conservation law is why physicists are so interested in looking at the energy balance of anything. Because we understand the energy balance of our Earth, we also know that global warming is caused by greenhouse gases – which have caused the largest imbalance in the radiative energy budget over the last century.

If the greenhouse effect (that checks the exit of longwave radiation from Earth into space) or the amount of absorbed sunlight diminished, one would see a slowing in the heat uptake of the oceans. The measurements show that this is not the case.

The increase in the amount of heat in the oceans amounts to 17 x 1022 Joules over the last 30 years.  That is so much energy it is equivalent to exploding a Hiroshima bomb every second in the ocean for thirty years.

The data in the graphs comes from the World Ocean Database.  Wikipedia has a fine overview of this database.  The data set includes nine million measured temperature profiles from all of the world’s oceans.  One of my personal heroes, the oceanographer Syd Levitus, has dedicated much of his life to making these oceanographic data freely available to everyone.  During the Cold war that even landed him in a Russian jail for espionage for a while, as he was visiting Russia on his quest for oceanographic data (he once told me of that adventure over breakfast in a Beijing hotel).

How to deny data

Ideologically motivated “climate skeptics” know that these data contradict their claims, and respond … by rejecting the measurements. Millions of stations are dismissed as “negligible” – the work of generations of oceanographers vanish with a journalist’s stroke of a pen because what should not exist, cannot be. “Climate skeptics’” web sites even claim that the measurement uncertainty in the average of 3000 Argo probes is the same as that from each individual one.  Thus not only are the results of climate research called into question, but even the elementary rules of uncertainty calculus that every science student learns in their first semester.  Anything goes when you have to deny global warming.  Even more bizarre is the Star Trek argument – but let me save that for later.

Slowdown in the upper ocean

Let us look at the upper ocean (for historic reasons defined as the upper 700 m):

Change in the heat content of the upper 700 m of the oceans.  Source: NOAA

And here is the direct comparison since 1980:

Changes in the heat content of the oceans.  Source:  Abraham et al., 2013.  The 2-sigma uncertainty for 1980 is 2 x 1022 J and for recent years 0.5 x 1022 J

We see two very interesting things.

First:  Roughly two thirds of the warming since 1980 occurred in the upper ocean.  The heat content of the upper layer has gone up twice as much as in the lower layer (700 – 2000 m).  The average temperature of the upper layer has increased more than three times as much as the lower (because the upper layer is only 700 m thick, and the lower one 1300 m).  That is not surprising, as after all the ocean is heated from above and it takes time for the heat to penetrate deeper.

Second:  In the last ten years the upper layer has warmed more slowly than before.  In spite of this the temperature still is changing as rapidly there as in the lower layer.  This recent slower warming in the upper ocean is closely related to the slower warming of the global surface temperature, because the temperature of the overlaying atmosphere is strongly coupled to the temperature of the ocean surface.

That the heat absorption of the ocean as a whole (at least to 2000 m) has not significantly slowed makes it clear that the reduced warming of the upper layer is not (at least not much) due to decreasing heating from above, but rather mostly due to greater heat loss to lower down:  through the 700 m level, from the upper to the lower layer.  (The transition from solar maximum to solar minimum probably also contributed a small part as planetary heat absorption decreased by about 15%, Abraham, et al., 2013).  It is difficult to establish the exact mechanism for this stronger heat flux to deeper water, given the diverse internal variability in the oceans.

Association with El Niño

Completely independently of this oceanographic data, a simple correlation analysis (Foster and Rahmstorf ERL 2011) showed that the flatter warming trend of the last 10 years was mostly a result of natural variability, namely the recently more frequent appearance of cold La Niña events in the tropical Pacific and a small contribution from decreasing solar activity.  The  effect of La Niña can be seen directly in the following figure, without any statistical analysis.  It shows the annual values of the global temperature with El Niño periods highlighted in red and La Niña periods in blue.  (Weekly updates on the current El Niño situation can be found here.)

Global surface temperature (average of the three series from NOAA, NASA and HadCRU).  Years influenced by El Niño are shown in red, La Niña influenced years in blue.  Source:  Climate Central, updated figure from the World Meteorological Organization (WMO) p. 15.

One finds that both the red El Niño years and the blue La Niña years are getting warmer, but given that we have lately experienced a cluster of La Niña years the overall warming trend over the last ten years is slower.  This can be thought of as the “noise” associated with natural variability, not a change in the “signal” of global warming (as discussed many times before here at RealClimate).

This is consistent with the finding that reduced warming is not mainly a result of a change in radiation balance but due to oceanic heat storage. During La Niña events (with cold ocean surface) the ocean absorbs additional heat that it releases during El Niño events (when the ocean surface is warm). The next El Niño event (whenever it comes – that is a stochastic process) is likely to produce a new global mean temperature record (as happened in 2010).

Kevin Trenberth, who has recently published a paper on this topic, explains the increased heat uptake in the deep ocean:

The reason for the change is a specific change in the winds, especially in the subtropical Pacific, where the trade winds have become noticeably stronger.  That altered ocean currents, strengthening the subtropical sea water circulation thus providing a mechanism to transport heat into the deeper ocean.  This is related to the decadal weather pattern in the Pacific associated with the La Niña phase of the El Niño phenomenon. 

New results from climate modelling

A study by Kosaka and Xie recently published in Nature confirms that the slowing rise in global temperatures during recent years has been a result of prevalent La Niña periods in the tropical Pacific.  The authors write in the abstract:

Our results show that the current hiatus is part of natural climate variability tied specifically to a La Niña like decadal cooling. 

They show this with an elegant experiment, in which they “force” their global climate model to follow the observed history of sea surface temperatures in the eastern tropical Pacific. With this trick the model is made to replay the actual sequence of El Niño and La Niña events found in the real world, rather than producing its own events by chance.  The result is that the model then also reproduces the observed global average temperature history with great accuracy.

There are then at least three independent lines of evidence that confirm we are not dealing with a slowdown in the global warming trend, but rather with progressive global warming with superimposed natural variability:

1.  Our correlation analysis between global temperature and the El Niño Index.

2.  The measurements of oceanic heat uptake.

3.  The new model calculation of Kosaka and Xie.

Beam me up Scotty!

Now to the most amusing attempt of “climate skeptics” to wish these scientific results away.  Their argument goes like this:  It is not possible that warming of the deep ocean accelerates at the same time as warming of the upper ocean slows down, because the heat must pass through the upper layer to reach the depths. A German journalist put it this way:

Winds can do a lot, but can they beam warm surface waters heated by carbon dioxide 700 meters further down? 

This argument reveals once again the shocking lack of understanding of basic physics in “climate skeptic” circles.  First the alleged problem is lacking any factual basis – after all, in the last decades the upper layer of the oceans has warmed faster than the deeper (even if recently not quite as fast as before).  What is the problem with the heat first warming the upper layer before it penetrates deeper? That is entirely as expected.

Second, physically there is absolutely no problem for wind changes to cool the upper ocean at the same time as they warm the deeper layers.  The following figure shows a simple example of how this can happen (there are also other possible mechanisms).

The ocean is known to be thermally stratified, with a warm layer, some hundreds of meters thick, lying on top of a cold deep ocean (a).  In the real world the transition is more gradual, not a sharp boundary as in the simplified diagram.  Panel (b) shows what happens if the wind is turned on. The surface layer (above the dashed depth level) becomes on average colder (less red), the deep layer warmer.  The average temperature changes are not the same (because of the different thickness of the layers), but the changes in heat content are – what the upper layer loses in heat, the lower gains. The First Law of Thermodynamics sends greetings.

Incidentally, that is the well-known mechanism of El Niño: (a) corresponds roughly to El Niño (with a warm eastern tropical Pacific) while (b) is like La Niña (cold eastern tropical Pacific). The winds are the trade winds.  The figure greatly exaggerates the slope of the layer interface, because in reality the ocean is paper thin.  Even a difference of 1000 m across the width of the Pacific (let’s say 10,000 km) leads to a slope of only 1:10,000 – which no one could distinguish from a perfectly horizontal line without massive vertical exaggeration.

Now if during the transition from (a) to (b) the upper layer is heated by the greenhouse effect, its temperature could remain constant while that of the lower one warmed. Simple classical physics without beaming.

Beam me up Scotty!  There is no intelligent life on this planet.

Links

Tamino provides his usual detailed analysis of the new study by Kosaka and Xie.

Dana Nuccitelli in the Guardian on the same paper with some further interesting aspects that I have not talked about here.

Another important point that is often forgotten in the discussion:  The data hole in the Arctic that explains part of the reduced warming trend (maybe even more than previously thought).

And a reminder:  The warming trend of the 15-year period up to 2006 was almost twice as fast as expected (0.3°C per decade, see Fig. 4 here), and (rightly) nobody cared. We published a paper in Science in 2007 where we noted this large trend, and as the first explanation for it we named “intrinsic variability within the climate system”. Which it turned out to be.

Recent Literature:

Levitus et al. (Geophysical Research Letters 2012). Documentation of the heat increase in the world’s oceans since 1955.  Included are uncertainty analyses, maps of the measurement coverage and many illustrations of the regional and vertical distribution of the warming.

Balmaseda et al. (Geophysical Research Letters 2013) shows among other things that El Niño events are associated with a strong loss of heat from the oceans.  As discussed above, during an El Niño the ocean loses heat to the surface because the surface of the ocean (see Fig. (a) above) is unusually warm.  Further, during volcanic eruptions the ocean cools but for another reason: because volcanic aerosols shade the sun and thus the oceans are heated less than normal.

Guemas et al. (Nature Climate Change 2013) shows that the slower warming of the last ten years cannot be explained by a change in the radiative balance of our Earth, but rather by a change in the heat storage of the oceans, and that this can be at least partially reproduced by climate models, if one accounts for the natural fluctuations associated with El Niño in the initialization of the models.

Abraham et al. (Reviews of Geophysics 2013). Very recent, wide ranging review of temperature measurements in the oceans with a detailed discussion of the accuracy of the data, planetary energy balance and the effect of the warming on sea levels.


158 Responses to “What ocean heating reveals about global warming”

  1. 51
    Clj says:

    @44
    The subtropical gye and Ekman transport only happens in the upper ocean (upper 700m), doesn’t it? If it is, how the heats are transporting downward and links to ENSO? (ENSO is also a signal in the upper ocean 700m). Is the heat transportation to the deeper 700m ocean due to vertical mixing or change of general circulation??

    Thanks!

    [Response: Both. Vertical diffusion is slower, but happens over most of the oceans, while downward advection of anomalously warm water happens in fewer spots but is faster (the North Atlantic, 'Mode' water formation regions north of the Antarctic Circumpolar Current, shelf water formation in Antarctica). Tidal mixing (particularly around the coasts may also be playing a role. - gavin]

  2. 52
    Arne Melsom says:

    @48 If your speculation is correct, I assume that another consequence would be that, if/when concentrations of greenhouse gases start to drop, corresponding reductions in surface ocean/land temperatures would take place at a much slower rate than would otherwise be the case: the surplus heat stored in the deep ocean will gradually make its way to the ocean surface, and continue to warm the atmosphere for decades, if not longer.

    (I think that an anomalously warm ocean surface heated from below would lead to more evaporation, and the additional water vapor would give a positive greenhouse effect that would partially offset the effect of a drop in greenhouse gas concentrations.)

  3. 53
    prokaryotes says:

    Thanks Rob for mentioning the ocean gyres. Further was all this forecasted, again Rob Painting wrote a very good blog on this topic too, in June of this year.

    A climate model-based study, Meehl (2011), predicted that this was largely due to anomalous heat removed from the surface ocean and instead transported down into the deep ocean. This anomalous deep ocean warming was later confirmed by observations.

    This deep ocean warming in the model occurred during negative phases of the Interdecadal Pacific Oscillation (IPO), an index of the mean state of the north and south Pacific Ocean, and was most likely in response to intensification of the wind-driven ocean circulation.
    Meehl (2013) is an update to their previous work, and the authors show that accelerated warming decades are associated with the positive phase of the IPO. This is a result of a weaker wind-driven ocean circulation, when a large decrease in heat transported to the deep ocean allows the surface ocean to warm quickly, and this in turn raises global surface temperatures.
    This modelling work, combined with current understanding of the wind-driven ocean circulation, implies that global surface temperaures will rise quickly when the IPO switches from the current negative phase to a positive phase.

    Link

  4. 54
    Alan Millar says:

    53
    Arne Melsom says:
    26 Sep 2013 at 9:41 AM

    “(I think that an anomalously warm ocean surface heated from below would lead to more evaporation, and the additional water vapor would give a positive greenhouse effect that would partially offset the effect of a drop in greenhouse gas concentrations.)”

    How does the extremely cold water (2-3C)of the deep ocean, warm the 18C ocean surface water precisely?

    [Response: It doesn't. However the gradient of temperature in the ocean is maintained (roughly) as a balance between mixing from above and advection of cold water (from the poles) below. If the surface cools, there is an anomalous heat flux up which will lead to a cooler deep ocean. This is simply a reduction in the downward heat flux, not an absolute counter-gradient flux. - gavin]

    Alan

  5. 55
    tokodave says:

    “Response: Because that’s where we live. – gavin”

    Thanks Gavin, I needed a laugh. It’s nice to remind people of some of the real fundamentals. We don’t live in the PETM, we live here and now and this is the only climate we’ve got. It’s worth repeating the closing statement from the recent American Meteorological Society Climate Change Statement: Prudence dictates extreme care in accounting for our relationship with the only planet known to be capable of sustaining human life.

  6. 56
    Chopbox says:

    Gavin,
    Just want to make sure I understand your response to Downpuppy’s query regarding translating heat into degrees (#11). There you said “10^23 J in the ocean … ~= 0.04ºC”
    1. Am I right to think that the heat figure being discussed (10^23 J) is calculated from temperature changes measured by these Argo bouys, and that your calculation is actually running in reverse from some earlier calculation that derived the heat figure? (That is, which came first?)
    2. If so, how much confidence should we have in the ability of these scientific instruments to measure temperature of the ocean that accurately?
    I don’t know anything about them, and hope you can tell me.

    [Response: The changes being measured are much larger than 0.04C since the variations in temperature are not even in space and time. Temperature changes are much larger near the surface, and there are substantial regional variations. The mean temperature change or the OHC increase is an integral over all of that and therefore can be estimated to higher precision than any individual reading (just like for the weather station record). The uncertainties due to sampling and measurement accuracy go into the error bars, and the trend is clearly significant. - gavin]

  7. 57
    prokaryotes says:

    Meehl et al. (2011)

    Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods

    There have been decades, such as 2000–2009, when the observed globally averaged surface-temperature time series shows little increase or even a slightly negative trend1 (a hiatus period). However, the observed energy imbalance at the top-of-atmosphere for this recent decade indicates that a net energy flux into the climate system of about 1 W m−2 (refs 2, 3) should be producing warming somewhere in the system4, 5. Here we analyse twenty-first-century climate-model simulations that maintain a consistent radiative imbalance at the top-of-atmosphere of about 1 W m−2 as observed for the past decade. Eight decades with a slightly negative global mean surface-temperature trend show that the ocean above 300 m takes up significantly less heat whereas the ocean below 300 m takes up significantly more, compared with non-hiatus decades. The model provides a plausible depiction of processes in the climate system causing the hiatus periods, and indicates that a hiatus period is a relatively common climate phenomenon and may be linked to La Niña-like conditions.

  8. 58
    prokaryotes says:

    The general pattern of warming and ocean circulation in the model, during these hiatus periods, is very similar to that which occurs over shorter timeframes in the La Niña phase of ENSO. Strong upwelling in the equatorial eastern Pacific brings cold water up from the deep, which cools air temperatures in this region. Meanwhile in the subtropics of each hemisphere, heat is piling up and being driven down into deeper layers.

    [..]

    Not only does the climate model-based study, Meehl (2011), show heat is buried into deeper ocean layers when global surface temperatures stall, but it also presents plausible mechanisms in ocean circulation that transport heat down to the deep ocean. The general pattern of sea surface temperature during these hiatus periods is very reminiscent of a La Niña-like climate state.

    The regular nature of these hiatus decades in the climate model, indicate that they are simply periods of natural variability, which occur even in the presence of a long-term warming trend. This is supported by historic observations (Figure 1), which shows roughly decade-long hiatus periods in upper ocean heat content during the 1960s to 1970s, and the 1980s to 1990s.

    The natural variability ‘flip-side’ to these hiatus decades, are periods where there is greater-than-average surface warming (see inset in Figure 2). So at some point in the very near future we can probably expect surface temperatures to gather up a head of steam, and begin rising at a rapid rate.

    Link

  9. 59
    Rob Painting says:

    @52 – No, the subtropical gyres can reach down into the deep ocean. See the observations in Roemmich & Gilson (2009) – The 2004-2008 mean and annual cycle of temperature, salinity, and steric height in the global ocean from the Argo program. Only a snapshot of course, but note where the deep ocean warming (as indicated by the mean steric height over the period) is occurring.

    Ekman transport may be confined to the surface layers, but when the circulation spins up, the greater rotational speed of the gyre increases the rigidity of the Taylor column at its centre. The gyre shifts poleward and the column lengthens. The sum effect is to displace isopycnals (parcels of water of the same density) vertically in the column, i.e. the deep ocean warms. May be easier if you understand that the circulation in the surface layers is not closed, there is transport/seepage.

    As for ENSO. See figure 5(a) & (b) in Stefan’s post. Imagine the left-hand side is the western tropical Pacific Ocean, and the right-hand side the eastern tropical Pacific. When the easterly trade winds strengthen during La Nina it pushes water along the equator from the east to west. This occurs because the Coriolis Force is zero at/near the equator. That isn’t the case as one moves further away from the equator. Anyway, much of the heat is forced down below the surface in the west. That is one reason why sea level rise in the western Pacific basin is much higher than the global average throughout the period of satellite-based observation (1993-to present) – the wind-driven circulation moved to a more intense phase throughout the duration of satellite altimetry. Based on past observations, dating back to the 19th century, this is unlikely to last.

  10. 60
    t_p_hamilton says:

    Think of the ocean heating during La Nina as removing $80 monthly from a deposit of $100 monthly for a net deposit of $20 . During El Nino, you are removing only $70 monthly, for a net deposit of $30. Alana Miller asks: how can a withdrawal add $10 a month?

  11. 61
    Paulw says:

    But isn’t the ocean heat storage far, far, smaller than the GHG forcing/net human-made forcing.

    The 0-2000 metre ocean is only absorbing 0.5 W/m2/yr but the net Human forcing is going to be reported by the IPCC tomorrow as 2.3 W/m2/yr.

    [Response: Just W/m2, no 'per year' involved. The 2.3 W/m2 number is radiative forcing with respect to atmospheric conditions in 1750, and it would be roughly the imbalance you would get instantly if you swapped in present day CO2 concentrations etc. Given that the planet has already warmed up, some of that forcing has already been responded to. Indeed, if the forcing increased slow enough (or the Earth responded faster - for instance, if there weren't any oceans), the temperature rise would basically just follow the forcing and you'd be hard pressed to detect an imbalance. The ~0.5W/m2 is the *remaining* imbalance and thus an indication of how much more the planet needs to warm in order to come to equilibrium (at constant atmospheric concentrations). - gavin]

  12. 62
    Martin says:

    Is there any reason to believe that after these La Niña dominated years climate warming will ‘play catch-up’?
    That is should we expect greater than normal warming until we reach the average warming of the last decades (revert to the mean)?
    Or does this pause mean that it will take approximately 15 years longer to reach the global temperatures projected for the end of this century?

    [Response: Depends on exactly what is going on. The portion associated with ENSO won't delay anything - you'd get back to the long term trend once we have a few El Niños. The portion associated with short term forcings (solar, unaccounted-for volcanic aerosols, undercounts of Chinese pollution) will depend on their long term evolution - if they stabilise, you'd get a delay. Any portion associated with a model over-sensitivity would imply a lower trend in the future. - gavin]

  13. 63
    Russ R. says:

    “10^23 J in the ocean = 2.8 x 10^8 J/m2 = 1.4 x 10^5 J/m2 over 2000 m depth ~= 1.4 x 10^2 J/kg ~= 0.04ºC (averaged over the whole depth). Much bigger changes are near the top though. – gavin”

    What is the measurement uncertainty of the temperature data that underlies the heat content calculation?

    Are there even thermometers that can reliably measure a difference of 0.04ºC?

    [Response: See above - gavin]

  14. 64
    KR says:

    Paulw – Net forcing changes since the Industrial revolution (about 1.6 W/m^2 in AR4) are not the same thing as the current top of atmosphere radiative imbalance (about 0.5-0.6 W/m^2 over the last 30 years based on OHC) as the climate has warmed over that time, and has already reacted to much of that net forcing change. You are confusing a rate with a summation.

    The only way for the TOA imbalance to be equal to the net forcing change would be for the Earth to somehow not warm over the last 250 years in the presence of that imbalance. And that’s not the case.

  15. 65
    Nick O. says:

    Will the rate of sea level rise, due to ocean warming and thermal expansion, be somewhat faster than predicted in previous reports? Thus the fact of the heat being stored more in the deep oceans is NOT some sort of climatic get-out-of-jail-free card?

  16. 66
  17. 67
    prokaryotes says:

    Re hiatus cooling periods, from Meehl et al. (2013)

    From five climate model runs of the 21st century the authors derive 500 years worth of simulations. The hiatus decades were chosen based on a slight cooling trend in global surface temperatures of less than -0.08°C per decade. Eight decades match this criteria and the composite of their surface temperature trends are shown in Figure 1(a). If a zero decade-long temperature trend were chosen as well, then there are many more decades that fall under that criteria, including three instances where no warming lasts for 14 years, and one where this persists for 15 years.

    For the accelerated warming decades the authors choose decades where the global surface warming is at least 0.41°C per decade (around twice the observed warming over the last few decades based on GISTEMP). Like the hiatus decades, these large values for the accelerated warming decades were chosen so that the trends were obvious. The composite of the trends for these accelerated decades are shown in Figure 1(b).

    It is apparent in Figure 1, that the hiatus and accelerated warming decades are virtually the mirror image of each other. The warm sea surface temperatures in the gyres, during hiatus decades, indicate convergence of near-surface currents and strong downwelling of heat. With accelerated decades the vertical, and poleward, transport of heat by the gyres seems to shutdown, enabling strong sea surface warming in the tropics – where most solar radiation enters the ocean. The strong warming in the polar regions is related to changes in the thermohaline circulation.

    Link

  18. 68
    Alan Millar says:

    58
    prokaryotes says:
    26 Sep 2013 at 2:44 PM

    “Not only does the climate model-based study, Meehl (2011), show heat is buried into deeper ocean layers when global surface temperatures stall, but it also presents plausible mechanisms in ocean circulation that transport heat down to the deep ocean. The general pattern of sea surface temperature during these hiatus periods is very reminiscent of a La Niña-like climate state.”

    It is fine to have a hypothesis but you need a physical mechanism to go along with it.

    The oceans are stratified, warmer water floats on top of the huge volume of deeper ocean that is at maximum density and minimum temperature.

    Whilst cold water can sink as its density increases, say as it is cooled at the poles, warm water cannot do this. Without significant up or down currents, heat can only be exchanged by convection and that is a heck of a slow process. There are significant horizontal currents even in the lowest layer but apart from places where these currents hit continental land masses there is no way to get much up or down currents.

    [Response: See above - gavin]

    So how does this increased heat get down there? It would have to be a fast process or we would see significant heating of the ocean surface, which I don’t believe we have seen this century.

  19. 69
    prokaryotes says:

    Nick O, #65: Will the rate of sea level rise, due to ocean warming and thermal expansion, be somewhat faster than predicted in previous reports?

    This is very likely, because El Nino years getting warmer and are tied to anomalously high sea levels.

    Patterns of anomalously high sea levels are attributed to El Niño–related changes to atmospheric pressure over the Gulf of Mexico and eastern Canada and to the wind field over the Northeast U.S. continental shelf.
    Climatologies of sea level anomalies (>0.05 m) and daily-mean storm surges (>0.3 m) are presented for the 1960–2010 cool seasons (October–April) along the East Coast of the United States. (Sweet & Zervas 2011) Link

    One finds that both the red El Niño years and the blue La Niña years are getting warmer, but given that we have lately experienced a cluster of La Niña years the overall warming trend over the last ten years is slower. This can be thought of as the “noise” associated with natural variability, not a change in the “signal” of global warming.

    This is consistent with the finding that reduced warming is not mainly a result of a change in radiation balance but due to oceanic heat storage. During La Niña events (with cold ocean surface) the ocean absorbs additional heat that it releases during El Niño events (when the ocean surface is warm). The next El Niño event (whenever it comes – that is a stochastic process) is likely to produce a new global mean temperature record.

  20. 70
    Russ R. says:

    “The uncertainties due to sampling and measurement accuracy go into the error bars, and the trend is clearly significant.”

    Then shouldn’t the error bars be displayed?

    [Response: The graphs are I think direct pulls from the NODC website, but we show the errors in our own publications i.e. right hand panel here:
    - gavin]

    And you didn’t actually answer the question about the measurement accuracy of the thermometers being used. (If you don’t know, that’s perfectly acceptable… I’ve tried looking for the info on the ARGO website, and can’t find it.)

    [Response: CTDs measure at the thousandth of the degree level. Argo floats will be similar. Errors associated with sampling are the bigger issue. - gavin]

  21. 71
    Alan Millar says:

    I obviously meant conduction not convection in my last post. Doh!!

    Alan

  22. 72
    prokaryotes says:

    So how does this increased heat get down there?

    Rob Painting: The transport of heat down into the surface to deep ocean occurs via the subtropical ocean gyres. These are large rotating masses of water, in each ocean basin, where ocean currents converge at their centre and are forced downwards, taking warm surface water with them. Link

    Kevin Trenberth: We have just published a new analysis showing that in the past decade about 30% of the heat has been dumped at levels below 700m, where most previous analyses stop. The first point is that this is fairly new, it is not there throughout the record. The cause of the change is a particular change in winds, especially in the Pacific Ocean where the subtropical trade winds have become noticeably stronger, thereby changing ocean currents and increasing the subtropical overturning in the ocean, providing a mechanism for heat to be carried down into the ocean. This is associated with decadal weather patterns in the Pacific, which are in turn related to the La Niña phase of the El Niño phenomenon.

    The second point is that we have found distinctive variations in global warming with El Niño: a mini global warming, in the sense of a global temperature increase, occurs in the latter stages of an El Niño event, as heat comes out of the ocean and warms the atmosphere. There are also distinctive volcanic eruption signals in the ocean heat content record. So these affect the perceptions of global warming. Normal weather also interferes by generating clouds that reflect the sunshine, and there are fluctuations in the global energy imbalance from month to month. But these average out over a year or so. Another prominent source of natural variability in the Earth’s energy imbalance is changes in the sun itself, seen most clearly as the sunspot cycle. From 2005 to 2010 the sun went into a quiet phase and the warming energy imbalance is estimated to have dropped by about 10 to 15%.

    Some of the penetration of heat into depths of the ocean is reversible, as it comes back in the next El Niño. However, a lot is not: instead it contributes to the overall warming of the deep ocean that has to occur for the climate system to equilibrate. It speeds that process up faster than generally assumed. It means less short term warming at the surface but at the expense of a greater earlier long-term warming, and faster sea level rise. So this has consequences. Link

  23. 73
    Alan Millar says:

    60
    t_p_hamilton says:
    26 Sep 2013 at 3:29 PM

    “Think of the ocean heating during La Nina as removing $80 monthly from a deposit of $100 monthly for a net deposit of $20 . During El Nino, you are removing only $70 monthly, for a net deposit of $30. Alana Miller asks: how can a withdrawal add $10 a month?”

    This is not the same at all. This heat is hypothesised to be going into the deeper ocean which is extremely cold and is stratified.

    How does it ever get back out to warm the troposphere?

    [Response: Please read the previous responses. (Clue: it doesn't). - gavin]

    If somehow and I can’t possibly imagine how, there was a huge increase in circulation between the surface and the deeper layers of the ocean, that would be disastrous for global temperatures but not upwards but downwards!

    Be thankful that the we are insulated from the huge volume of cold waters that comprise the ocean, because if it ever became far more mixed with the surface layers we would plunge into permanent glaciation.

    [Response: No - they would just warm up (just like they do everywhere there is upwelling). - gavin]

    Alan

  24. 74
    Ray Ladbury says:

    Alan Millar,
    OK, think about this. Heat is transferred into the deep by winds increasing mixing. If warm water is mixing down, then cold water is mixing up, right. Now the water down below warms. The next time there is mixing, the water above won’t cool quite as much.

  25. 75
    Alan Millar says:

    “[Response: No – they would just warm up (just like they do everywhere there is upwelling). – gavin”

    We must be at cross purposes here Gavin because a much more well mixed ocean would be disastrous for surface layer temperatures and the impact on the Troposphere.

    The average temperature of all the oceans water is about 4c compared to the average of 17/18c for just the surface layer.

    Alan

    [Response: I am aware. But you are thinking as if this is a closed system. It is not. Water at the surface that is below the equilibrium temperature will be warmed mainly radiatively until it warms up again. If the ocean was completely well mixed this would take a long time, and the total heat content would roughly quadruple by the time it stabilized. It would be an easy experiment to try in a GCM. – gavin

  26. 76
    Desertphile says:

    For the past two years I have offered a US$1,000 wager to anyone (denialists or sane people) that rejects the proposition that there will be a new global high temperature record set within five years. I have made the offer to many hundreds of denialists, and none of them will take the bet. Golly, it’s almost as if they do not believe what they claim to believe.

  27. 77
    Alan Millar says:

    Response: “I am aware. But you are thinking as if this is a closed system. It is not. Water at the surface that is below the equilibrium temperature will be warmed mainly radiatively until it warms up again. If the ocean was completely well mixed this would take a long time, and the total heat content would roughly quadruple by the time it stabilized. It would be an easy experiment to try in a GCM”. – gavin

    I am aware it is not a closed system, that is my problem.

    How, is it managing to receive all this increased energy and not significantly heat up the Troposphere, for which there is a quick mechanism for doing so, yet at the same time can heat up the deep layers of the ocean, for which there does not appear to be a quick mechanism to do so?

    [Response: Sorry, I'm not getting your point. The energy comes from the sun, and the ocean is heated from the surface. You posited a well mixed ocean (which implies infinite diffusion) so that is your mechanism for warming the deep. In the real world there are the mechanisms I listed above. - gavin]

  28. 78
    JCH says:

    AM is suggesting water is trapped at depth. I have read references to the Peru-Chile Trench that described it as the site of significant upwelling. The trench is very deep.

    If you watch animations of La Nina, the trench is clearly visible as the source of very cold water. You can watch it spread out all the way across the equator. One wonders if we were to fill the trench, would ENSO as we know it survive?

    From what depth is this upwelling coming? I cannot believe it is not coming from very deep in the trench, the bottom of which is some 20,000 feet below the surface.

  29. 79
    KK Aw says:

    Gavin, your response to my question is like the drunk man looking for his keys under the streetlight. Man: Where did you lose your keys? Drunk: Over there. Man: Why are you looking for them here? Drunk: It is bright here.

  30. 80
  31. 81
    Chris Colose says:

    KK Aw,

    It is not unreasonable to focus on the “sphere” where we (and many other species) live. Just because 2% is small compared to 90% doesn’t mean the 2% is unimportant. Global warming would be a non-issue if it were occurring on a lifeless planet like Mars (not that the deep ocean is lifeless, but much of what we care about is at the surface).

    Scientifically, global warming is defined in terms of surface (or near surface temperature) change, and this extends throughout the troposphere too. It is also a better understood metric than the changes in OHC. People have interest in different things, and this is useful: there is no one metric that fully encompasses what is going with a changing climate.

  32. 82
    Sven says:

    Gavin
    “[Response: Changing a unit to have a small sounding number doesn't actually change anything; neither the significance nor the accuracy. But if you want to play rhetorical games, go right ahead - though perhaps not here. - gavin]
    Isn’t it temperature in Centigrade that is originally measured by the ARGO floats? And if so, why change the unit in the first place?

    [Response: The relevant phenomena is the heat flux and so it's measured in Joules, J/m2 or perhaps better, W/m2 to get the rate of change. If you were talking about direct temperature effects on fisheries or corals or something, degrees C would be more appropriate. - gavin]

  33. 83
    Rob Painting says:

    @ 73 – “This heat is hypothesised to be going into the deeper ocean…

    See figure 1 in Stefan’s post. The deep ocean warming has been measured. Even if readers don’t understand the principles of oceanography it doesn’t matter, the warming of the deep ocean is taking place regardless.

    which is extremely cold and is stratified.

    You have that backwards. It’s the surface oceans that are stratified. The deep-abyssal ocean is relatively well-mixed. If you think about it just a little it’s straightforward to work out why.

    If somehow and I can’t possibly imagine how, there was a huge increase in circulation between the surface and the deeper layers of the ocean, that would be disastrous for global temperatures but not upwards but downwards!”

    Science is not constrained by your inability to understand how the wind-driven ocean circulation works, or to ignore explanations provided earlier in this comment thread. Anyway, didn’t Stefan already cover this contrarian meme in his Star Trek (quantum teleportation) argument?

    And no, there is no huge plunge in tropical or global surface air temperatures when the ocean circulation spins up because there is a near-compensating decrease in poleward heat transport via the atmospheric circulation. As the ocean circulation takes up the role of transporting heat poleward the atmospheric circulation spins down. When the ocean circulation is sluggish the atmosphere spins up. A good explanation of the details is provided here: Koll & Abbot (2013) – Why Tropical Sea Surface Temperature is Insensitive to Ocean Heat Transport Changes. They conclude:

    The goal of this paper was to explain why tropical SST is not strongly affected by changes in OHT. We find that higher OHT weakens the Hadley circulation,which reduces reflective cloud cover and, to a lesser extent, reduces the surface winds that sustain evaporation, allowing SST to remain almost constant over a large range of OHT states

    Now I suspect this information will have no effect on you, but as always this is really written for the benefit of rational readers. Science may not have all the answers, but there is a great deal more known about the ocean circulation than contrarians try to insinuate.

  34. 84
    Ray Ladbury says:

    kk AW,
    Were I a Coelecanth, I might find your criticism valid.

  35. 85
    Ray Ladbury says:

    I believe that Alan Millar is engaging in the fallacy of
    Argumentum sine filo.

  36. 86
    mike says:

    Question: when ice melts, does that not result in the storage of large amounts of latent heat in the meltwater? If there has been an aceleration in ice melt in Greenland and Antarctica, the meltwater must contain latent heat that would otherwise have gone into the atmosphere. If this is the case, how much of the heat entering into the ocean system rather than into the atmosphere is this latent heat?

  37. 87
    Ray Ladbury says:

    Mike,
    The “latent heat” in water would only be released if it froze again.

  38. 88
    robert says:

    @39 — Bryson, no. “Heat”, the noun, is quite pedantically and standardly defined in physics as energy transferred due to a temperature differential. The energy you refer to, the kinetic energy of random atomic and molecular motions, is termed “thermal energy.” Reference any freshman physics text on this matter…

  39. 89
    Alan Millar says:

    83
    Rob Painting says:
    27 Sep 2013 at 4:11 AM

    and

    85
    Ray Ladbury says:
    27 Sep 2013 at 8:39 AM

    “I believe that Alan Millar is engaging in the fallacy of
    Argumentum sine filo”

    I am well aware of ocean circulation that interchanges water to and from the deep oceans.

    Again it is the time scales that is the problem. These Thermohaline circulations take hundreds of years or longer. The wind driven coastal upwellings are a tiny fraction of the ocean surface and volume.

    If the surface layer of the ocean is not quickly exchanging energy with the troposphere, which it can do easily and quickly but retaining the energy, why is it not heating up far more rapidly, If you are saying it is getting rid of it to the deep oceans, how precisely is it doing this so quickly?

    Please be precise about the mechanisms, volumes and timescales, just saying ocean circulations is not good enough, given what we know about the very long timescales involved to move the water.

    Alan

  40. 90
    Hank Roberts says:

    Alan Millar, in the original post at the top of the page, your question was answered before you asked it.

    … the wind is turned on. The surface layer … becomes on average colder (less red), the deep layer warmer…. like La Niña (cold eastern tropical Pacific). The winds are the trade winds….

    Remember — “If the Earth was an apple … the water layer would be thinner than the fruit’s skin”

    You’re confused by being very small, seeing the ocean as deep, vast, and its depths unreachable.

    Look at some of what’s been described just in the last few years. If you don’t want to make the effort to use Scholar, just look at, for example, Science Daily and search there. You’ll find, just as examples:
    “… another — possibly substantial — source of energy for mixing that’s generated in the ocean where cold, heavy water collides with warm, light water. … turbulence at a front near Japan that is 10 to 20 times more energetic than what the wind could generate…. is likely an extreme example of a process that occurs much more widely in the ocean.

    “It’s not just wind at work on the ocean. The enhanced mixing at this front is drawing energy from the entire North Pacific. That’s what’s really new”

    and

    “… sea water mixes dramatically as it rushes over undersea mountains in Drake Passage — the channel between the southern tip of South America and the Antarctic continent. Mixing of water layers in the oceans is crucial in regulating Earth’s climate and ocean currents.

    The research provides insight for climate models which until now have lacked the detailed information on ocean mixing ….

  41. 91
    Hank Roberts says:

    Oh, and just because this stuff is wonderful — I mentioned this when the study came out, but I don’t know if the modelers have enough information to add it in:

    From 2009: “Kakani Katija and John Dabiri at the California Institute of Technology have developed a way to estimate the extent of “biogenic” mixing. After conducting field measurements on swimming jellyfish, they built models of how animals mix the waters ocean-wide and concluded that the effect may be extensive.

    “Swimming animals may contribute to ocean mixing on the same level as winds and tides,” says Katija. “This necessitates the inclusion of biogenic mixing sources in ocean circulation and global climate models.”

    And where are those organisms active? Well, that changes day to day. Tough to model, but living organisms aren’t trivial in affecting how climate works, and changes in what’s alive where and when are feedbacks to climate change.

  42. 92

    I tried posting this yesterday and for some reason nothing happened so here goes again…

    The critical point we must not forget is that an increase in GHG creates an energy flow imbalance by slowing down the rate of energy loss to space from outgoing radiation. The only way you can balance the equation is by a temperature increase to increase outgoing radiation (or by changing the atmosphere in the opposite direction). If there is a “pause” in temperature change while the oceans absorb the excess, this isn’t a good thing. We are just changing the order of events a bit because an increase in surface temperatures would in any case eventually increase the energy content of the oceans.

    I have an article on one of my blogs about why we need to focus on energy.

    Ideally we should measure this energy imbalance directly but I seem to recall reading a James Hansen paper where he quantifies the net flow and explains why we cannot measure the difference between inflow and outflow to sufficient accuracy using satellites. But I would have thought rather direct indications of an increase in net planetary energy like rapid loss of Arctic sea ice should be enough to convince anyone that there has been no “slowdown”.

  43. 93
    Rob Painting says:

    @89 – You misunderstand. It’s not my job to educate you about oceanography, that’s your job. You don’t appear to have read the papers I have previously referenced, so it appears ideological blinkers are preventing you from accepting the scientific evidence. This was apparent earlier in the thread, when you claimed the deep ocean warming was hypothesized. This despite the fact that the first graph in Stefan’s post stands out like a sore thumb, and shows the observed warming of the ocean down to 2000 metres.

    Why exactly should the ocean behave according to a hypothesis you appear to have formulated whilst sitting on your sofa? My advice would be to undertake tertiary studies in oceanography, then you actually understand the topic you erroneously think you know so much about, and can make some of the basic calculations yourself. Here’s a hint though: Earth’s rotation, and the division of the ocean into basins by the continental land mass configuration, play a large role in Ekman pumping and suction.

  44. 94
    Ray Ladbury says:

    Alan, we aren’t talking thermohaline transport. We’re talking wind-driven mixing. Not the same.

  45. 95
    Alan Millar says:

    94
    Ray Ladbury says:
    27 Sep 2013 at 1:47 PM

    “Alan, we aren’t talking thermohaline transport. We’re talking wind-driven mixing. Not the same”

    I figured that is the only probable mechanism but where is this taking place in the volumes necessary to rid the upper layer of the extra energy so quickly?

    The coastal wind driven upwellings are well known and they drive a good proportion of the world’s shipping industry. Has there been a change there?

    Even so the proportion and volumes involved, of the total volumes, look far to small to get rid of the surface layers excess energy, nowhere near enough interchange.

    Where is this change in wind driven interchange happening and in what volumes? If it was very significant it would surely have a noticeable regional affect on troposphere temperatures which we would become aware of.

    Alan

  46. 96
    Alan Millar says:

    Doh!

    Mean ‘fishing’ industry obviously.

    Alan

  47. 97
    Ray Ladbury says:

    Alan, read the papers in the recent literature section cited above.

  48. 98
    Hank Roberts says:

    Alan, glancing at what’s readily accessible from where you’re sitting would help you — otherwise you’re asking us to go find the review articles in the field and summarize them for you. If you let people know how much you’ve found out by looking, experts may show up to fill in real gaps. Asking questions that way works better.

    “What is important about X” is a homework-help question.

  49. 99
    Michael Sweet says:

    I thought the comments up thread about coal aerosols in China were interesting. Is there a relationship between the cooling these aerosols cause and the increase in trade wind strength? Could this be estimated using a climate model?

  50. 100
    Stuart Poss says:

    Recently, there has been considerable discussion of increasing Antarctic ice pack caused by increased winds. Since the Eastern Tropical Pacific is not entirely decoupled from West Wind Drift given the general pattern of circulation in the SE Pacific, the question arises is the magnitude of the observed overall energy difference in the recently observed “extended” La Nina phase of ENSO condition relative to the the “more normal” ENSO comparable in magnitude to energy associated with the apparent increase in winds and potentially currents around the Antarctic? Could such a coupling or partial coupling explain where the energy for a more “normal” ENSO is going? That is could the energy “missing or delayed” be going instead into a modified current pattern in SE Pacific?

    Presumably, it does take a lot of energy to move that much water faster, with the heat potentially being redistributed into deeper ocean layers associated with perhaps poorly understood fluctuations of the Antarctic convergence at depth? Or is it that the wind phenomenon of such short/local scale or that the circulation systems are known to be so completely decoupled that this isn’t possible and that some other explanation for the delay in the “normal” ENSO pattern is required?

    Are there good overviews as to how much annual/decadal variation there is in world ocean currents and could unexpected aspects of “trends” in their coupling explain where all the additional trapped energy is going?

    Of course, all this is of interest to an ichthyologist potentially interested in understanding where to look for expected changes in fish distributions given the tremendous diversity of depths occupied by different groups of fishes.


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