Update May 19, 2015 text added at end.

We hear a lot about CO2 as climate’s “control knob, but about the oceans’ pacemaker, AMOC? Not so much.

In the Water World post, I referenced the match between SSTs (sea surface temperatures) as recorded in HadISSAT and the IPO, an index of SSTs in the Eastern Pacific: North, Central and South. This is a brief discussion of the Atlantic role in shaping climate patterns, especially in Europe and North America.

The Big Picture

Since global average temperatures are dominated by the oceans as measured by SSTs, it is significant that multidecadal cycles are presently shifting from warmer phases to cooler. The PDO entered its cooler period recently, and the current weak El Nino is evidence of this. (Pacific Decadal Oscillation is an index of Northeastern Pacific based upon ~30-year periods, warm when El Ninos dominate, and cool when La Ninas rule.)

Atlantic Multidecadal Oscillation (AMO). Source: http://www.appinsys.com/globalwarming/SixtyYearCycle.htm

Now the focus is on the Atlantic SSTs and what to expect from the AMO (Atlantic Multidecadal Oscillation), which has peaked and is likely to trend downward. In the background is a large scale actor, the Atlantic Meridional Overturning Circulation (AMOC) which is the Atlantic part of the global “conveyor belt” moving warm water from the equatorial oceans to the poles and back again.

The notion of the AMOC as the climate pacemaker derives from its role in conveying Pacific shifts into the Atlantic.

“An index of AMOC variability is defined, and the manner in which key variables covary with it is determined. In both models the following is found. (i) AMOC variability is associated with upper-ocean (top 1 km) density anomalies (dominated by temperature) on the western margin of the basin in the region of the Mann eddy with a period of about 20 years. These anomalies modulate the trajectory and strength of the North Atlantic Current. The importance of the western margin is a direct consequence of the thermal wind relation and is independent of the mechanisms that create those density anomalies. (ii) Density anomalies in this key region are part of a larger-scale pattern that propagates around the subpolar gyre and acts as a “pacemaker” of AMOC variability. (iii) The observed variability is consistent with the primary driving mechanism being stochastic wind curl forcing, with Labrador Sea convection playing a secondary role.”

http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-11-00460.1

The Atlantic Leading the Stadium Wave

The critical role of the AMOC and the Atlantic’s global influence is described as part of a “stadium wave” by which the effects ripple throughout all the ocean oscillations.

“A warm (cool) Atlantic triggers a cascade of polarity changes in participating teleconnections, resulting in a cooling (warming) hemispheric climate signal about 30 years later – the “stadium wave”. The periodicity of changes in the North Atlantic AMO appears to be largely governed by the Atlantic sector of the meridional overturning circulation (AMOC). As the cascade of atmospheric and lagged oceanic teleconnections converts a warm (cool)-Atlantic-born signal into a Pacific cooling (warming) signal, the AMOC is re-configuring the Atlantic SST signature. By the time the Pacific begins to cool (warm) as a result of an initially warm (cool) North Atlantic, the North Atlantic, itself, is cooling (warming). The conflated result of temperature profiles within each oceanic basin is a cooling (warming) hemisphere, poised to reverse trend as a result of the once-again-cooling (warming) North Atlantic SSTs (which will ultimately lead to a warming (cooling) climate). No conclusion on what exactly causes the NHT is given, just that it strongly coincides with the trends of combined PDO and AMO.”
Marcia Wyatt comment here:

On The AMO+PDO Dataset

A draft of Wyatt et al (2011) can be read here:

Click to access 1WKT_2012_author_manuscript.pdf

What is the AMOC up to these days?

 

“We have shown that there was a slowdown in the AMOC transport between 2004 and 2012 amounting to an average of −0.54 Sv yr−1 (95 % c.i. −0.08 to −0.99 Sv yr−1) at 26◦ N, and that this was primarily due to a strengthening of the southward flow in the upper 1100 m and a reduction of the southward transport of NADW below 3000 m. This trend is an order of magnitude larger than that predicted by climate models associated with global climate change scenarios, suggesting that this decrease represents decadal variability in the AMOC system rather than a response to climate change. (lower North Atlantic deep water (LNADW) upper (UNADW) . . .our observations show no significant change in the Gulf Stream transport over the 2004–2012 period when the AMOC is decreasing.”

Click to access os-10-29-2014.pdf

Implications for AMO and Atlantic SSTs

“The poleward transport of heat in the sub-tropical North Atlantic has been shown (Johns et al., 2011) to be highly correlated with the Atlantic meridional overturning circulation (AMOC). One petawatt (PW = 1015 W) of heat carried by the AMOC is released to the atmosphere between 26◦ N and 50◦ N and has important impacts on the climate of the North Atlantic region (e.g. Srokoz et al., 2012). The AMOC varies on a range of timescales (e.g. Eden and Willebrand, 2001; Kanzow et al., 2010) and is thought to have played a key role in rapid climate change in the past (Ganopolski and Rahmstorf, 2001).”

Click to access Kerr%20Science%2005.pdf

“A speed up (slow down) of the AMOC is in favor of generating a warm (cold) phase of the AMO by the anomalous northward (southward) heat transport in the upper ocean, which reversely leads to a weakening (strengthening) of the AMOC through changes in the meridional density gradient after a delayed time of ocean adjustment. This suggests that on multidecadal timescales the AMO and AMOC are related and interact with each other.”

Click to access Zhang_Wang_JGR2013.pdf

Are we on the cusp of oceanic climate change?

“Sometime after the turn of the century the Atlantic Multidecadal Oscillation peaked.  Due to the volatility of the data and the short time frame, it’s tough to determine when it peaked. But for illustration purposes, Figure 2 compares the same two sea surface temperature data subsets starting in 2003.  The surface of the North Atlantic has cooled slightly over that time, while the surfaces of the rest of the global oceans show very little warming.”

New Study Predicts a Slight Cooling of North Atlantic Sea Surface Temperatures over the Next Decade

“The AMO tracks to the solar irradiance with a lag of about 8-9 years. This suggests the current warm AMO state will end by around 2015. Northern Hemispheric temperature will take a leg down. With the cooling of the Pacific now and more La Ninas, look for net cooling especially in the tropics until then.” Joseph D’Aleo

Click to access AMO_Important_in_Northern_Hemispheric_Anomalies.pdf

Update May 19, 2015

Dr. William Gray in his 2012 paper:

“The global surface warming of about 0.7°C that has been experienced over the last 150 years and the multi-decadal up-and-down global temperature changes of 0.3-0.4°C that have been observed over this period are hypothesized to be driven by a combination of multi-century and multi-decadal ocean circulation changes. These ocean changes are due to naturally occurring upper ocean salinity variations. Changes in CO2 play little role in these salinity driven ocean climate forcings. “

A great deal of AMOC explanation is available in Dr. Gray’s paper:

Click to access gray2012.pdf

Included are excellent diagrams and charts, such as these:

Following Dr. Bernaerts’ discussion that Oceans Make Climate, and that naval activity has an effect, this post overviews issues concerning the heat flux at the boundary between sea surface and atmosphere.

The Basics

The graph displays measures of heat flux in the sub-tropics during a 21-day period in November. Shortwave solar energy shown above in green labeled radiative is stored in the upper 200 meters of the ocean. The upper panel shows the rise in SST (Sea Surface Temperature) due to net incoming energy. The yellow shows latent heat cooling the ocean, (lowering SST) and transferring heat upward, driving convection.

From
An Investigation of Turbulent Heat Exchange in the Subtropics
James B. Edson

“One can think of the ocean as a capacitor for the MJO (Madden-Julian Oscillation), where the energy is being accumulated when there is a net heat flux into the ocean (here occurring to approximately November 24) after which it is released to the atmosphere during the active phase of the MJO under high winds and large latent heat exchange.”

Click to access mmedson.pdf

Turbulence Changes Both Parts of the Heat Flux

As mentioned above, this flux is not in equilibrium or steady state, but constantly subject to turbulence, both natural and man-made. Therein lies the difficulty in measuring it accurately and documenting changes over time. The study above, while not addressing ships, shows that latent heat varies considerably with turbulence.

“Turbulence in the surface layer of the ocean contributes to the transfer of heat, gas and momentum across the air-sea boundary. As such, study of turbulence in the ocean surface layer is becoming increasingly important for understanding its effects on climate change.”

“Moving surface vessels such as ships typically produce wakes which are highly visible in ocean SAR images, where the region behind the vessel displays a region of wake turbulence and surface currents which produce a visible backscattering response.”

Click to access osd-9-2851-2012-print.pdf

Turbulence Changes the Ocean Albedo

Schematic of a typical turbulent ship wake as viewed by SAR.
Measurement of turbulence in the oceanic mixed layer using Synthetic Aperture Radar (SAR)
S. G. George and A. R. L. Tatnall 2012

The incoming solar energy is reduced by the “bright water” resulting from air bubbles and foam in the wake.

“The albedo change over land caused by land‐use and land‐cover modifications is well documented [Forster et al., 2007]. However, modification of the ocean albedo by human activities is unknown, even though the oceans cover 70% of Earth’s surface and absorbs approximately 93% of incident solar radiation.”

“This study provides new insights into ship‐generated disturbances on the ocean surface, which have received little attention in climate studies, but is potentially significant for the ocean‐ atmosphere energy balance and could affect climate.”

“The strong enhancement of ocean reflectance in the ship wake is unambiguous, and >100% in most cases in the spectral range from the ultraviolet to the near‐infrared (0.340 mm ≤l≤ 2.205 mm), and clearly seen in the ocean BRDF measurements. These results are derived from angular and spectral measurements of the intensity of reflected solar radiation from an airborne instrument over several regions of the ocean disturbed by the ship wakes. The implication for the global radiation budget at the top of the atmosphere has been demonstrated in this study.”
Gatebe et al 2011
http://onlinelibrary.wiley.com/doi/10.1029/2011GL048819/pdf

However authors of this study do not estimate albedo effect from shipping to be significant at this time.

“Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%. We assessed the importance of this increase to climate forcing, where we estimated the global radiative forcing of ship wakes to be -0.00014 plus or minus 53% Watts per square meter assuming a global distribution of 32331 ships of size of greater than or equal to 100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (-0.007 to +0.02 Watts per square meter), but considering that the global shipping fleet has rapidly grown in the last five decades and this trend is likely to continue because of the need of more inter-continental transportation as a result of economic globalization, we argue that the radiative forcing of wakes is expected to be increasingly important especially in harbors and coastal regions.”

There are some efforts to measure the infrared signature of ship wakes, including emitted energy.

“The sea surface turbulent trailing wake of a ship, which can be rather easily observed in the infrared by airborne surveillance systems, is a consequence of the difference in roughness and temperature between the wake and the sea background. We have developed a phenomenological model for the infrared radiance of the turbulent wake by assuming that the sea surface roughness is dependent upon the turbulent intensity near the sea surface. . .Given the incident solar, atmospheric, and sky infrared radiances, we calculate the reflected and emitted sea surface radiance from both the wake and the background. We compare the infrared contrast of the wake with infrared image data obtained in an airborne trial.”

Modeling the turbulent trailing ship wake in the infrared
Vivian Issa and Zahir A. Daya 2014
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA555507

Conclusion

Ocean turbulence is being studied but not as extensively as atmospheric turbulence. In both domains, drawing climate conclusions is challenging. There is an albedo effect of a ship’s wake that reflects solar SW, but one study considers it a small effect. The release of latent heat varies significantly with wind changes, but the effect from shipping is not known. Other ocean effects from shipping are not discussed here, such as additional release of CO2 and ice-breaking in the Arctic .

Updated on April 9 and 11 at bottom of post.

In response to my water world post, I was shown the wonderful phrase coined by Dr. Bernaerts:

“Climate is the continuation of oceans by other means”.

In was in 1992 he wrote in Nature appealing to the Rio conference to use the UN Convention on the Law of the Seas (UNCLOS) to better manage human impacts on the oceans, and thereby address climate concerns. Needless to say, that call fell on deaf ears.

He later elaborates: “Presumably science would serve the general public better when they would listen to Leonardo da Vinci (1452-1519) who said: “Water is the driver of nature”. Some say that nature rules climate, but water rules the nature on this earth, and the water on earth is so synonymous with the oceans and seas that it can be said: Climate is the continuation of the oceans by other means.”

Dr. Bernaerts is certainly a man worthy of respect and admiration–an expert in maritime law, a passionate marine conservationist, and an historian of naval warfare. All of these are subjects where I have little background knowledge and much to learn.

I see him as a spokesman for ocean scientists, whose views have been little considered in the IPCC rush to judgment upon CO2. Dr. Bernaerts says quite a lot about this at his website: http://www.whatisclimate.com/

It takes some time to understand how his material is organized, with several websites to explore, but there’s lots of data, naval history, graphs and charts to peruse and expand one’s understanding.

An Overview

My comments here are a first attempt to understand his point of view with respect to climate change. Bernaerts makes this observation:

“In the mid 20th Century there had been a 35-year lasting period of global cooling, which had started between 1940 and 1945. The reasoning for causation given by climate science is rather limited, and hardly sufficient. Cooling was evident in the Pacific as well. Could naval war in the Pacific over just three years have contributed to trigger a climatic shift in the North Pacific? If it was not naval war, which mechanism caused the large discontinuity in the mid-twentieth century in observed global-mean surface temperatures? Was it a “natural event”, or by what kick off was this process set in motion?”

While admitting answers are not definitive, he goes on to assert:
“In the North Atlantic and its adjacent seas the naval war in Northern Europe definitely contributed highly. This is due to a much higher extension of the northern North Atlantic towards the pole, and the sensible structure of the warm Gulf Current system that flows through colder water up to the Arctic Ocean . One has to assume that any substantial climatic shift generated in the North Atlantic will inevitably show its impact on the North Pacific as well.”

This leads into a discussion of the PDO:

“While naval activities, just like any wind, have an impact on the upper sea surface layer concerning the temperature and salinity structure, the vastness of the North Pacific in extension and volume, makes it hard to assume any relevance between WWII and the observed climate shift in the early 1940s. But as long as the reason for the shift has not been evidently established, naval war activities need to be regarded as an option, and should not have been ignored. The question is about the impact human activities may have on climate, and this should be known completely as soon as possible. For this reason this investigation restricts the scope on the so-called Pacific Decadal Oscillation (PDO).”

“Until now no mechanism has been identified to explain the shifts. They are rare, and occurred only six times over the last 300 years: 1750, 1905, 1946, 1977, 1998, and 2008 (Biondi, 2001). Concerning the last century N. Mantua identifies two full PDO cycles: with cool PDO regimes from 1890-1924 and again from 1947-1976, while warm PDO regimes dominated from 1925-1946 and from 1977 through (at least) the mid-1990’s (Mantua, 2000), whereby timing may vary according to the researcher, e.g. saying that a warm phase lasted from 1925–42 that turned into a cold PDO cycle from 1943–76 (Zhang, 1996).”

Although the sea surface temperature (SST) data taken during WWII should only be used with caution (Bernaerts, 1996), they need nevertheless be assessed with regard to timing. But the shift in SST and SAT (surface air temperature), show a different time, first in the Europe/Atlantic area (between 1940 and 1942), and in the North Pacific between 1942 and 1945. The set of given SST graphics indicate, at best that pre WWII warming continued maximally until about 1942.”

Elsewhere he theorizes that the stirring action of great and increasing numbers of propeller-driven vessels releases ocean heat into the air, beyond what naturally occurs. He doesn’t claim this is proven, but rather it has been ignored and not studied. He also believes that future cooling is as likely as warming, contrary to what consensus scientists expect.

I appreciate Dr. Bernaerts’ perspective and will be reading more of his extensive work.

Update April 11:  Recent Analyses

Offshore Wind-parks and mild Winters.
Contribution from Ships, Fishery, Wind-parks etc.
25th February, 2015

Click to access k-.pdf

After a moderate March now a cold April? April 4, 2015
http://climate-ocean.com/2015/K-m2.html

Update: Comments by Dr. Bernaerts and myself

Dr. Bernaerts responds here:

https://rclutz.wordpress.com/2015/04/09/understanding-how-oceans-have-driven-climate-change/