This new paper from Lee et al just published in GRL has an answer. It seems warm water is being transported from the Indian Ocean via the Agulhas leakage.
Abstract:
As the upper layer of the world ocean warms gradually during the 20th century, the inter-ocean heat transport from the Indian to Atlantic basin should be enhanced, and the Atlantic Ocean should therefore gain extra heat due to the increased upper ocean temperature of the inflow via the Agulhas leakage. Consistent with this hypothesis, instrumental records indicate that the Atlantic Ocean has warmed substantially more than any other ocean basin since the mid-20th century.
A surface-forced global ocean-ice coupled model is used to test this hypothesis and to find that the observed warming trend of the Atlantic Ocean since the 1950s is largely due to an increase in the inter-ocean heat transport from the Indian Ocean. Further analysis reveals that the increased inter-ocean heat transport is not only caused by the increased upper ocean temperature of the inflow but also, and more strongly, by the increased Agulhas Current leakage, which is augmented by the strengthening of the wind stress curl over the South Atlantic and Indian subtropical gyre.
Citation: Lee, S.‐K., W. Park, E. van Sebille,
M. O. Baringer, C. Wang, D. B. Enfield, S. G. Yeager, and B. P.
Kirtman (2011), What caused the significant increase in Atlantic
Ocean heat content since the mid‐20th century?, Geophys. Res.
Lett., 38, L17607, doi:10.1029/2011GL048856.
Figure 1A is quite interesting, showing a good match between the modeling and observation:
for the Atlantic basin from 30°S to 75°N”]
And figure 1B shows where the heat transport is coming from:
h/t to Dr. Leif Svalgaard.
The paper here
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Hockey, anyone?
Of course, the models captured this.
Then the Indian Ocean, which is smaller than the Atlantic, must be cooling drastically?
Brian H says:
September 8, 2011 at 12:36 am
Then the Indian Ocean, which is smaller than the Atlantic, must be cooling drastically?
————————————————————————————————————–
I seem to recall from a piece Bob Tisdale posted here, that La Nina isn’t always the opposite of El Nino. The Indian ocean basin warms during both, and only cools when ENSO is neutral. As the period in question here saw less neutral conditions than the norm this could be the root cause of the warming.
OHT in North Atlantic since 1955. Something happened recently.
http://climexp.knmi.nl/data/iheat700_North_Atlantic.png
I bet Bob T. will quantify the ENSO-Indian ocean link and the rest will be history.
Sorry, what leakage? They always choose words carefully. The Agulhas current is a massive warm current, it flows round Africa and overwhelms/mixes with the Antarctic upwelling and forms the Benguela current heading north in the Atlantic.
The only leakage in this uniform flow system is the weak counter current close to the coast that flows north back into the Indian Ocean.
As the poster says, The Indian Ocean must be a water boiler.
Apologies for repeating this in more than one thread but it is relevant in each case.
It seems to be a little more complicated than clouds simply being a negative or positive feedback because latitudinal cloud distribution is also very important and the oceanic response to cloudiness changes confounds the initial expectation. Hence the significant rise in Atlantic Ocean heat content since the mid 20th century.
As I explain below the solar input to the tropical oceans increases when the sun is more active and it takes a while for that energy to circulate round the globe from the Pacific and into the Atlantic where it hangs around for quite a while because of the bottleneck in flow into the Arctic Ocean.
What I think happens is that for whatever reason the atmosphere expands when the sun is active and contracts when it is inactive.
In the process the temperature of the stratosphere and mesosphere changes oppositely to the sign of the temperature change in thermosphere and troposphere.
The effect is to draw the tropopause upward when the sun is active and push it down when the sun is less active. Globally averaged of course.
The outcome is latitudinal shifting of all the components of the surface air pressure distribution which changes the sizes and positions of the climate zones.
That changes the energy budget via the speed of the water cycle AND cloud quantities because that process changes the length of the air mass boundaries which is where mixing occurs to produce clouds.
So an active sun tries to COOL the system by changing the structure of the atmosphere to let energy OUT of the system FASTER via the higher tropopause but in the process cloud bands are drawn poleward to let more energy into the oceans in the tropics which offsets the faster energy loss to space.
So the cloud changes provide an indirect negative (warming) response to counter the direct solar cooling effect via the coolr stratosphere and mesosphere.
The position regarding bottom up effects from periodically faster energy release from the oceans or more energy in the air from more GHGs is different. In that case the extra warmth at lower levels pushes the tropopause up as before and in that case the increased energy into the oceans is a positive feedback. However the poleward shift of the surface air pressure systems accelerates the speed of energy transfer to space which is a negative response sufficient to cancel out both the extra energy from the oceans or GHGs AND the extra solar energy into the system.
Thus whatever changes the vertical temperature profile of the atmosphere from above or below will cause cloudiness changes that then exert a negative response either by adjusting energy flow into the oceans or by adjusting energy flow out to space as necessary to maintain equilibrium and what we then experience is shifting climate zones as the speed of energy flow through the system varies.
That is a neat solution to the problem.
It is the vertical temperature profile of the atmosphere that is key whether caused by top down solar effects or bottom up oceanic or GHG effects because that then causes the cloudiness changes.
It sounds complex and it is but it is no more complex than it needs to be to fit observations.
Brian H says:
September 8, 2011 at 12:36 am
Then the Indian Ocean, which is smaller than the Atlantic, must be cooling drastically?
No, it’s getting even hotter from the back-convected Atlantic it’s heating, it will soon boil away altogether.
Leaving a big hole in the ocean.
Brian H, tut! Where is your global warming theory text book. The heat from the Indian Ocean comes from the Pacific Ocean which comes from the Atlantic Ocean which is warmer because of the heat from the Indian Ocean. I ran it through my Scalectrix model car set and it came right back to the start. Proof that all cars in the world finish up where they started.
So where does the heat in the Indian Ocean come from?
Variations in Agulhas leakage may explain some of the difference between the South Atlantic and Indian Ocean OHC, and would help to explain why South Atlantic OHC has flattened in recent years…
http://i52.tinypic.com/25hool1.jpg
…while the Indian Ocean OHC has continued to rise:
http://i56.tinypic.com/4ikmtg.jpg
But it does not explain why the rise in North Atlantic OHC was double that of the South Atlantic and almost 4 times higher than the Indian Ocean:
http://i52.tinypic.com/25upt3l.jpg
It also does not explain why North Atlantic OHC has dropped so drastically since 2005:
http://i55.tinypic.com/219p6bm.jpg
Lee et al (2011) opens their concluding Discussions (page 5) with:
“Obviously, there remain many crucial questions. One such question is the role of basin‐scale low‐frequency climate variability such as the Atlantic multidecadal oscillation (AMO) and the Pacific decadal oscillation on the differential inter‐ocean warming. In particular, the AMO, which arguably results from the natural oscillation of the AMOC driven in the North Atlantic sinking regions [e.g., Knight et al., 2005; Lee and Wang, 2010], may have directly contributed to the rapid warming of the Atlantic Ocean since the 1950s.”
The graphs above are from the following post:
http://bobtisdale.wordpress.com/2011/06/19/january-to-march-2011-nodc-ocean-heat-content-0-700meters-update-and-comments/
Thanks for the copy, Leif.
The President of the Sychelles blamed the recent shark attacks on the water temperature in the area falling so attracting the more aggressive sharks to appear. So maybe there is some milage in this theory.
Did CO2 cause the leakage?
“Brian H says:
September 8, 2011 at 12:36 am
Then the Indian Ocean, which is smaller than the Atlantic, must be cooling drastically?”
Or it could stay at it’s normal temperature by tapping in to Trenberth’s ‘missing heat’.
Eureka I’ve found it!!
Consistent with this hypothesis, instrumental records indicate that the Atlantic Ocean has warmed substantially more than any other ocean basin since the mid-20th century.
A surface-forced global ocean-ice coupled model is used to test this hypothesis and to find that the observed warming trend of the Atlantic Ocean since the 1950s is largely due to an increase in the inter-ocean heat transport from the Indian Ocean.
Right, run it through a PlayStation and call the exercise an experiment. If actual observations are consistent with the hypothesis, doesn’t that mean it’s the model that’s being tested? And they back this with a “simulated AMOC index” and a “simulated heat budget.” Why not cite actual observations of Indian Ocean heat content?
Ah, well, at least they didn’t bring out the dread CO2.
The Indian ocean is 140m higher than the Atlantic but that is due to the shape of the planet and gravity.
John Marshall says:
September 8, 2011 at 2:44 am
The Indian ocean is 140m higher than the Atlantic but that is due to the shape of the planet and gravity.
=================================================================== No wonder the slow boat to China took so long if it had to climb up an 140m hill.
Grey lensman – as someone who has swum on both sides of the African subcontinent i would like to point out emphatically that the Agulhas does not overwhelm the Antarctic upwelling to form the Benguela. The Benguela current is the upwelling driven by prevailing winds-the sea is colder off the Namibian coast than further south. The desert climate has remained bonedry throughout the period.
Stephen. The president of the Seychelles needs a few stern words from Trenberth about going off message. Perhaps a resignation is in order.
Is the increase in Atlantic temperatures involved in the continuing low level of arctic summer ice? Is there much heat transport across the Equator? My geography lessons showed two very different circulations, north and south. I would like to have met the sailors (?) who kept such a fastidious record of temperatures in the Southern Oceans from 1870 into the 1900’s. Would it not be better to use temperature as an indicator (which is reality..see Al Gore) rather than “heat content” which is a cobbled together modelling invention?
criminogenic says:
September 8, 2011 at 1:52 am
So where does the heat in the Indian Ocean come from?
With all the brains at this site, I am amazed that no one else has realized the obvious answer: It’s Trenberth’s heat! The travesty is no more!
http://www.climate4you.com/images/HadCRUT3%20and%20TropicalCloudCoverISCCP.gif
All that extra energy has to go somewhere. How it got from the tropics to the north atlantic isn’t too hard to work out.
John Marshall says:
September 8, 2011 at 2:44 am
The Indian ocean is 140m higher than the Atlantic but that is due to the shape of the planet and gravity.
The Indian Ocean is generally depicted as the global low point on the Geoid.
http://en.wikipedia.org/wiki/File:Geoid_height_red_blue.png
So does this increase in heat correlate with annual Atlantic storm energy, or any other hypothesised destructive consequence of CAGW? Because looking at this
http://en.wikipedia.org/wiki/File:Atlantic_ace_timeseries_1850-2007.jpg
it appears not.
“Katherine says:
September 8, 2011 at 2:39 am
Consistent with this hypothesis, instrumental records indicate that the Atlantic Ocean has warmed substantially more than any other ocean basin since the mid-20th century.
A surface-forced global ocean-ice coupled model is used to test this hypothesis and to find that the observed warming trend of the Atlantic Ocean since the 1950s is largely due to an increase in the inter-ocean heat transport from the Indian Ocean.
Right, run it through a PlayStation and call the exercise an experiment. If actual observations are consistent with the hypothesis, doesn’t that mean it’s the model that’s being tested? And they back this with a “simulated AMOC index” and a “simulated heat budget.” Why not cite actual observations of Indian Ocean heat content?
Ah, well, at least they didn’t bring out the dread CO2.”
Ding, ding, ding. Prize goes to Ms Katherine for the outing…