Blizzard Jonas on the US east coast has just shattered snowfall records. Both weather forecasters and climate experts have linked the high snowfall amounts to the exceptionally warm sea surface temperatures off the east coast. In this post I will examine a related question: why are sea surface temperatures so high there, as shown in the snapshot from Climate Reanalyzer below?
I will argue that this warmth (as well as the cold blob in the subpolar Atlantic) is partly due to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), sometimes referred to as the Gulf Stream System, in response to global warming. There are two points to this argument:
(1) The warm sea surface temperatures are not just some short-term anomaly but are part of a long-term observed warming trend, in which ocean temperatures off the US east coast are warming faster than global average temperatures.
(2) Climate models show a “cold blob” in the subpolar Atlantic as well as enhanced warming off the US east coast as a characteristic response pattern to a slowdown of the AMOC.
Observed sea surface temperature change
A comprehensive analysis of the patterns of change in global sea surface temperatures since the 19th Century was performed by Dima and Lohmann (2010). The dominant pattern of change (technically these patterns are called EOF) is global warming – no surprise there. The second-most important pattern is more interesting and shown in Fig. 1.
Fig. 1 Second pattern of sea surface temperature change (i.e. EOF2) found in the HadISST global sea surface temperature data set. Source: Dima and Lohmann 2010.
This pattern shows a cold blob (shown in red here) developing in the subpolar North Atlantic, as well as a warm patch (shown in blue) developing off the US east coast. (The colors are reversed compared to what you might expect, as the observed change is composed of this pattern multiplied with a time series which shows a negative trend – so “red is warm” but with a negative trend, i.e. cooling.)
Dima and Lohmann also looked at the pattern correlation between North and South Atlantic, and they found this (Fig. 2):
Fig. 2 Pattern of coupled correlation of North Atlantic and South Atlantic sea surface temperatures. The correlation coefficient is 0.93.
This is very interesting, as the physical linkage between South and North Atlantic is the heat transport across the equator from South to North Atlantic, which is dominated by the AMOC. Dima and Lohmann concluded that the patterns shown in Fig. 1 and Fig. 2 indicate a change in the AMOC, and they wrote:
The global conveyor has been weakening since the late 1930s.
(As a side remark, the IPCC in its last report ignored this result and claimed, rather puzzling to me, that there is no evidence for an AMOC slowdown.)
It is noteworthy that in 2015, the “cold blob” region actually registered the coldest sea surface conditions since records began in 1880 – whilst the globe as a whole was record hot!
In our paper in Nature Climate Change last year (see our Realclimate post on this) we used sea surface temperature data specifically from the cold blob to diagnose AMOC variations and found an exceptional AMOC slowdown in the 20th Century, and we argued that Greenland mass loss may have made a significant contribution to this slowdown by helping to dilute ocean waters in the subpolar Atlantic.
Modelled response to an AMOC slowdown
Let’s have a look what climate models have to say about this. Fig. 3 shows the sea surface temperature response to a speed-up of the AMOC from a paper by Zhang et al. (2011) from the Geophysical Fluid Dynamics Lab in Princeton. This AMOC speedup was achieved by enhancing salinities near the sea bottom in the overflow of dense waters over the ridge between Greenland, Iceland and Scotland – a nice clean experiment that did not involve any deliberate changes introduced at the sea surface.
Fig. 3 Pattern of modelled sea surface temperature response to an enhanced AMOC. Source: Zhang et al. 2011.
The resulting pattern is very interesting indeed, and similar to what is observed (compare Figs. 1 and 2). For an AMOC slowdown you would get the reverse: a cold blob in the subpolar gyre region of the Atlantic, and a warm region off the US east coast.
In an earlier paper, Zhang (2008) presented this schematic view of the response to an enhanced AMOC (Fig. 4):
Fig. 4 Schematic of surface temperature response to an enhanced AMOC. Reverse the colours for the response to a weakened AMOC.
A very recent study by Saba et al. (2015) specifically analyzed sea surface temperatures off the US east coast in observations and a suite of global warming runs with climate models. They find that the highest resolution climate model can reproduce observed temperatures well, and it projects the following response to increased CO2 (Fig. 5):
Fig. 5 Sea surface temperature response to CO2 doubling in a high-resolution global climate model. Note the cold blob in the subpolar Atlantic and enhanced warming off the US east coast.
They find that the region off the US east coast warms “nearly three times faster than the global average”. They summarize their key finding as follows:
Both observations and the climate model demonstrate a robust relationship between a weakening Atlantic Meridional Overturning Circulation (AMOC) and an increase in the proportion of Warm-Temperate Slope Water entering the Northwest Atlantic Shelf.
Bottom Line
There is a strong case that the warm SST off the US coast and the cold blob in the subpolar gyre are linked, both being caused by an AMOC slowdown. This AMOC slowdown thus may have consequences for extreme weather in the US that I did not foresee in the past and only started to think about in the last year.
When Jake Gyllenhaal was snowed in in the New York public library in the film The Day After Tomorrow after an AMOC collapse, the physics may have been wrong, but perhaps there was a grain of truth in that snow storm after all.
Weblink
The Washington Post on this: The surprising way that climate change could worsen East Coast blizzards
References
- M. Dima, and G. Lohmann, "Evidence for Two Distinct Modes of Large-Scale Ocean Circulation Changes over the Last Century", Journal of Climate, vol. 23, pp. 5-16, 2010. http://dx.doi.org/10.1175/2009JCLI2867.1
- S. Rahmstorf, J.E. Box, G. Feulner, M.E. Mann, A. Robinson, S. Rutherford, and E.J. Schaffernicht, "Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation", Nature Climate Change, vol. 5, pp. 475-480, 2015. http://dx.doi.org/10.1038/nclimate2554
- R. Zhang, T.L. Delworth, A. Rosati, W.G. Anderson, K.W. Dixon, H. Lee, and F. Zeng, "Sensitivity of the North Atlantic Ocean Circulation to an abrupt change in the Nordic Sea overflow in a high resolution global coupled climate model", Journal of Geophysical Research, vol. 116, 2011. http://dx.doi.org/10.1029/2011JC007240
- R. Zhang, "Coherent surface‐subsurface fingerprint of the Atlantic meridional overturning circulation", Geophysical Research Letters, vol. 35, 2008. http://dx.doi.org/10.1029/2008GL035463
-
V.S. Saba, S.M. Griffies, W.G. Anderson, M. Winton, M.A. Alexander, T.L. Delworth, J.A. Hare, M.J. Harrison, A. Rosati, G.A. Vecchi, and R. Zhang, "Enhanced warming of the
N orthwestA tlanticO cean under climate change", Journal of Geophysical Research: Oceans, vol. 121, pp. 118-132, 2016. http://dx.doi.org/10.1002/2015JC011346
A minor grammatical comment: “There is two” since two is plural it should be there are two.
Excellent summary btw.
So could we say in layman speak that the warm waters off the east coast are piling up, as the sinking downstream weakens? Or is the fluid flow so complex that simple logic like this is inadequate?
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Very interesting indeed. Thanks. It’ll be intriguing to see how this idea (and this phenomenon) develop.
As an aside to the primary point regarding the slowdown of the Gulf Stream, please refrain from using non-scientific nomenclature such as referring to the recent snowstorm as “Joanas”. Winter storms are not nor have they ever been named by the National Weather Service or its parent agenct, the National Oceanic and Atmospheric Administration. Nor will they ever be. Only tropical systems are named. The entire naming process for winter storms was ginned up by the private sector, in this case, The Weather Channel for ratings. There are absolutely no scientific criteria whatsoever behind it (tropical systems names have specific criteria and thermodynamic properties). It is arbitrary, subjective and completely unscientific. Frankly, the use of winter storm names is a gross insult to the science of meteorology and it is quite sad to see it used at realclimate.org where anti-science climate deniers are frequently and correctly called out. So the use of such names comes across as a double standard re: science. And from a science perspective, quite wrong.
[Response: Thanks, I was not aware of the US conventions on naming weather systems. (But I don’t think using an unofficial name can be compared to climate denial…) -stefan]
In fig 2, do the colors indicate correlations ?
[Response: No, it’s a temperature pattern. There is an associated pattern in the South Atlantic that goes with it which I didn’t show in order to not overload the piece – for details check out the paper! -stefan]
For more on how Jonas and other winter storms get their names – Meet Jonas, Part Storm, Part Marketing Ploy. I.e., it’s the Weather Channel.
Ok, I promise I won’t use the name used in the media for the storm, as I now understand it’s an insult to the @NWS and @NOAA. What I’m not clear on are 2 things: what exactly is a @ColdBlob? and are you saying that this extreme, long-lasting weather anomaly is due to, no question about it, @GlobalWarming?
I wonder if the warm and cold water masses could be considered a Ocean blocking pattern, and btw Hansen etal. 2015
Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2◦C global warming is highly dangerous
Excerpts
Impact of ice melt on storms
Freshwater injection onto the North Atlantic and Southern Oceans causes increase of sea level pressure at middle latitudes and decrease at polar latitudes. These pressure changes have implications for the strength of prevailing winds and for severe weather. The robust increase of high pressure in the North Atlantic strengthens prevailing northeasterly winds blowing onto the Bahamas. The Eemian-age chevron beach structures with consistent southwesterly direction throughout windward shores in the Bahamas, with wave runup deposits at elevations as much as 20–40 m above today’s sea level and reaching as far as a few kilometers inland, must have been formed by massive storms in the direction of the prevailing winds.
Shutdown or substantial slowdown of the AMOC, besides possibly contributing to extreme end-Eemian events, will cause a more general increase of severe weather. This is shown by the change of zonal mean temperature and eddy kinetic energy in our simulations with and without ice melt. Without ice melt, surface warming is largest in the Arctic, resulting in a decrease of lower tropospheric eddy energy. However, the surface cooling from ice melt increases surface and lower tropospheric temperature gradients, and in stark contrast to the case without ice melt, there is a large increase of mid-latitude eddy energy throughout the midlatitude troposphere.
The increase of zonal-mean midlatitude baroclinicity that we find is in agreement with the localized, N. Atlantic-centered increases in baroclinicity found in the higher resolution simulations of Jackson et al. (2015) and Brayshaw et al. (2009). Increased baroclinicity produced by a stronger temperature gradient provides energy for more severe weather events.
Many of the most memorable and devastating storms in eastern North America and western Europe, popularly known as superstorms, have been winter cyclonic storms, though sometimes occurring in late fall or early spring, that generate near-hurricane force winds and often large amounts of snowfall (Chapter 11, Hansen, 2009).
Continued warming of low latitude oceans in coming decades will provide more water vapor to strengthen such storms. If this tropical warming is combined with a cooler North Atlantic Ocean from AMOC slowdown and an increase in midlatitude eddy energy, we can anticipate more severe baroclinic storms.
Increased high pressure due to cooler high latitude ocean can make blocking situations more extreme, with a steeper pressure gradient between the storm’s low pressure center and the blocking high, thus driving stronger North Atlantic storms. Large freshwater injection on the North Atlantic Ocean has a different impact on winds than freshwater injection on the Southern Ocean.
In the Southern Ocean the increased meridional temperature gradient increases the strength of the westerlies in all seasons at all longitudes. In the North Atlantic Ocean the increase of sea level pressure in the winter slows the westerlies. Thus instead of a strong zonal wind that keeps cold polar air locked in the Arctic, there is a tendency for more cold air outbreaks to middle latitudes.
Experiment definition: exponentially increasing fresh water
Greenland and Antarctica have outlet glaciers occupying canyons with bedrock below sea level well back into the ice sheet (Fretwell et al., 2013; Morlighem et al., 2014; Pollard et al., 2015). Feedbacks, including ice sheet darkening due to surface melt (Hansen et al., 2007b; Robinson et al., 2012; Tedesco et al., 2013; Box et al., 2012) and lowering and thus warming of the near-coastal ice sheet surface, make increasing ice melt likely. Paleoclimate data reveal instances of sea level rise of several meters in a century (Fairbanks, 1989; Deschamps et al., 2012). Those cases involved ice sheets at lower latitudes, but 21st century climate forcing is larger and increasing much more rapidly.
…Freshwater sensitivity in our model is similar to an earlier version of the model used 20 to simulate the 8.2 ky freshwater event associated with demise of the Hudson Bay ice dome (LeGrande et al., 2006). The ∼ 50 % AMOC slowdown in that model, in response to forcings of 2.5–5 Sv years indicated by geologic and paleohydraulic studies (e.g., Clarke et al, 2004), is consistent with indications from isotope-enabled analyses of the 8.2 ky event (LeGrande and Schmidt, 2008) and sediment records 25 from the northwest Atlantic (Kleiven et al., 2008). The 1–2 century AMOC recovery time in numerical experiments (LeGrande and Schmidt, 2008) seems consistent with the 160 year duration of the 8.2 ky cooling event (Rasmussen et al., 2013).
Storm-related model diagnostics
Ice melt in the North Atlantic creates a substantial increment toward higher sea level pressure in the North Atlantic region in all seasons. In the summer the added surface pressure strengthens and moves northward the Bermuda high pressure system. Circulation around the high pressure creates strong prevailing northeasterly winds in the North Atlantic at the latitudes of Bermuda and the Bahamas. A1B climate forcing alone has only a small impact on the winds, but cold meltwater in the North Atlantic causes a strengthening and poleward shift of the high pressure. The high pressure in the model is located further east than appropriate for producing the fastest possible winds at the Bahamas. Our coarse resolution (4◦ × 5◦) model, which slightly misplaces the pressure maximum for today’s climate, may be partly responsible for the displacement.
However, the location of high pressure also depends meltwater placement, which we spread uniformly over all longitudes in the North Atlantic between 65◦ W and 15◦ E and on specific location of ocean currents and surface temperature during the Eemian.
Our results at least imply that strong cooling in the North Atlantic from AMOC shutdown does create higher wind speed.
It would be useful to carry out more detailed studies with higher resolution climate models including the most realistic possible distribution of meltwater.
The increment in seasonal mean wind speed of the northeasterlies relative to preindustrial conditions is as much as 10–20 %.
Such a percentage increase of wind speed in a storm translates into an increase of storm power dissipation by a factor ∼ 1.4–2, because wind power dissipation is proportional to the cube of wind speed (Emanuel, 25 1987, 2005).
However, our simulated changes refer to seasonal mean winds averaged over large grid-boxes, not individual storms.
A blocking high pressure system in the North Atlantic creating consistent strong northeasterly flow would provide wave action that may have contributed to the chevron ridge formation in the Bahamas and Bermuda. This blocking high pressure system could contribute to powerful storm impacts in another way. In combination with the warm tropical conditions that existed in the late Eemian (Cortijo et al., 1999), and are expected in the future if GHGs continue to increase, this blocking high pressure could create a preferred alley for tropical storm tracks.
We assumed, in discussing the relevance of these experiments to Eemian climate, that effects of freshwater injection dominate over changing GHG amount, as seems likely because of the large freshwater effect on SSTs and sea level pressure. However, Eemian CO2 was actually almost constant at ∼275 ppm (Luthi et al., 2008). Thus, to isolate effects better, we now carry out simulations with fixed GHG amount, which helps clarify important feedback processes.
Related https://en.wikipedia.org/wiki/Cold_blob_(North_Atlantic)
I am very grateful for the time and effort you devoted to explain what is going on citing recent research and so shortly after the (Jonas) blizzard. This type of voluntary work from scientists helps a lot in understanding such extreme events in the light of science. Regards
Dan says:
24 Jan 2016 at 10:20 PM
“As an aside to the primary point regarding the slowdown of the Gulf Stream, please refrain from using non-scientific nomenclature such as referring to the recent snowstorm as “Joanas”. Winter storms are not nor have they ever been named by the National Weather Service or its parent agenct, the National Oceanic and Atmospheric Administration.”
I agree that it’s a cheap marketing ploy ginned up by the Weather Channel to make storms more appealing and sexy. If it proves popular with the kiddies I don’t expect it will go away anytime soon. Other media outlets have already accepted the practice as legit.
In other news… How quickly could the Gulf Stream circulation come to a halt? Do you expect to see Europe go into the deep freeze within the next 30 years or so? I do not trust the IPCC projections for “end of century” conditions, especially their projected SLR. I think the IPCC missed SLR completely. Their ultra-conservative assessment is not helpful in that people still think we have a lot of time to act. I don’t see any reason why Greenland ice couldn’t completely collapse in a relatively short amount of time. By collapse I don’t mean completely melt but maybe break into several large pieces. Thanks
An item of related interest that just appeared:
Yang, Qian, Timothy H. Dixon, Paul G. Myers, Jennifer Bonin, Don Chambers, and M. R. van den Broeke. “Recent Increases in Arctic Freshwater Flux Affects Labrador Sea Convection and Atlantic Overturning Circulation.” Nature Communications 7 (January 22, 2016): 10525. doi:10.1038/ncomms10525.
“…Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW [Labrador Sea Water] formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening.”
The link @5 does give argument against naming winter storms (from Joel N. Myers, the founder and president of AccuWeather aimed at the names originating from a commercial competitor The Weather Channel), but this side of the pond the UK & Irish Met Offices think that naming is a good thing and so the first storm Abigail was duly christened in November of last year, the first of six storms that rattled through the region in two months. Mind, it may not be the last word as this Met Office naming has been described as “a pilot project.”
Then it must be said that the continued use of the synonym “The Great Storm” for referring to ‘great storms’ has been getting beyond a joke although this may not be entirely due to AGW increasing the frequency of ‘great storms.’ It is perhaps worth noting that the Great Storm of 1703 was reportedly ” unprecedented in ferocity and duration” but this was also a time that was actually unprecedented for reports of all kinds. “News bulletins of casualties and damage were sold all over England – a novelty at that time. Likely in previous ‘great storms’, the ‘ferocity and duration’ may have been worthy of comment locally but only until the ‘ferocity and duration’ of the plague or some other arriving cataclysm made it appear all rather trivial.
[Response: I’m used to named winter storms from Germany – as far as I know named by the German weather service. -stefan]
In agreement with Chuck Hughes this time: If Europe goes into a deep freeze, the world is in trouble. So is this panic2.0? That would be the case if farming becomes too difficult in Europe. Europe would cease to be a place that produces food.
“The global conveyor has been weakening since the late 1930s.”
But no prediction of when or whether the general crop failure would happen.
For the US east coast, I think you aren’t talking about a shortening of the growing season. Snow is fine as long as it stays in the winter and you aren’t growing semi-tropical things like peaches and oranges. So it is only peaches and oranges that are impacted. 4 feet of snow is no big deal if you have enough snow plows and people know how to drive on snow. In that sense, more snow would help people learn to drive better.
Washington, D.C. needs a bit of waking up. More snow could help bring politicians to their senses.
Thanks Stefan. I was a little confused with the colour switches in the Figures. Let me know if I have this right.
Figures 1 and 2 show increases in SST in blue and decreases in red (with respect to a cooling trend). For the modelled responses, Figures 3 & 4 shows the same colour pattern but the reverse effect in response to enhanced AMOC. How is this ‘similar to what is observed’ – its the reverse of what’s observed isn’t it (which I think is the point)? In Figure 5 the modelled responses show warming off the E coast and cooling in the sub-polar gyre thus showing a similar response to what is shown in Figures 1 & 2. The colour scheme for Figures 3,4 & 5 switch to the opposite (more intuitive) colour scheme as compared to Figures 1 & 2. Is this right?
Also any comment on the likely impact this will have on the jet stream and on weather patterns in the UK (and Northern Europe) if this trend continues?
[Response: In all cases the temperature response to an AMOC change in models is consistent: an AMOC weakening causes a cold blob in the subpolar open Atlantic (south of Iceland) and a warming off the US east coast. And that is the temperature change that is indeed observed.
I can’t predict the impact on jet stream and weather patterns, we and others are still trying to understand this. -stefan]
Pat Michaels is at it again at WSJ.
Most likely the results of this mode are just more of what we’ve been seeing. Which while it includes more superstorms on both sides of the north Atlantic, it also seems to include more unseasonable heat waves as well. One question for the modelers, what impact on the net icemelt from Greenland is this AMOC slowdown likely to have? My guess it it probably slows it, hence there may be a stabilizing feedback.
Perhaps we should refer to The-Storm-That-Must-Not-Be-Named (especially for the denialists when confronted with the reality of the physics of the planetary heat engine…), or something along the line of the humerous exchange from the Vicar of Dibley episode ‘The Weather and the Window’.
More seriously though, and changing the subject, the ‘cold blob’ is only anomalously ‘cold’ because it’s largely relocated from an even colder area where its temperature is not relatively coldly anomalous, and in fact is warmly anomalous where it represents meltwater from ice affected by heat brought in from the tropics.
The ‘cold blob’ meme is in some ways reminiscent of the “pause”, where people fail to grasp the underlying phenomena that define the nature of shifts in the appearance of a temperature anomaly. It’s a notion that should be used with a little care, given the denialists’ propensity for twisting fact.
A few things seem odd here.
The largest positive SST anomalies in the arctic are located between Norway and Novaya Zemlya – where is this heat coming from if the area immediately to the southwest is cooling?
Shouldn’t a slowdown of the AMOC be self-limiting? Less heat transport from subtropical to polar latitudes should result in a cooling of the arctic and a reduction in melting. While past climate anomalies that have suggested slowdowns of the AMOC have been blamed on rapid injections of large quantities of freshwater, these are believed to have come from drainage of lakes of meltwater. This scenario does not shut down the poleward heat transport of the AMOC until after the melting is complete. If meltwater drains immediately, shouldn’t any AMOC slowdown that results be a strong negative feedback, with lower temperatures reducing melting?
[Response: If you look at our paper (in the reference list) you will find that we show a model run (Fig. 2b) in which the overturning north and south of the Iceland sill are actually anticorrelated. So you can’t conclude from an AMOC slowdown that it should get colder in the Arctic Ocean – the cold blob predicted by climate models is only south of Iceland (which is where it is observed).
Regarding feedbacks: yes, temperature does tend to give a negative feedback on AMOC changes, salinity a positive feedback (the latter is why there is a collapse threshold). Slower AMOC brings less salty water up from the south, leading to freshening in the deep water formation areas and thus an even weaker AMOC. First described by Henry Stommel in the 1950s. -stefan]
> AMOC slowdown thus may have consequences
> for extreme weather in the US
Has everyone read Kim Stanley Robinson (ten years ago) on this?
Fifty Degrees Belowhttps://www.sfsite.com/11b/fd212.htm
Re TWC winter storm naming and science: http://www.weather.com/news/news/science-behind-naming-winter-storms-weather-channel-20140121. There are also purely meteorological criteria and decisions involving ridges, troughs, jets and precipitation in regard to what constitutes a storm and its beginning/end.
Bernard J.
It’s fine, in the future we will likely have more and stronger snowstorms, and cold air intrusion into our latitudes, and freshwater cools. The colder waters, block some of the warmer, and this increases the temperature gradient (cold to warm difference), the fuel for storms, higher wind speeds, higher wave action. The days of the deniers are very limited, in face of the growing dangerous threat of climate change.
It is like having an obstruction in your cars radiator.. Slowly your engine starts to overheat…
re: 20. That proves my point. The link shows that the decision to name storms is primarily made by population density/impact area. Little if any meteorological science parameters.
Hank Roberts:
First thing I thought of when I saw this RC post. Gave my heart a lurch, it did. Can you imagine our world mobilizing to implement KSR’s solution?
Re 14: The region of warming off the U.S. East coast is probably too small to influence the jet stream or rossby waves. The cooling region south of Iceland, however, is broader and, together with warming in surrounding areas, might favour southward meanders of rossby waves over the Atlantic (or southward propagation of cold air if you want), which induces the opposite over Europe (northward propagation of warm air). Which might also increase (spatial) persistence of rossby wave patterns (blocking). Just a thought…
And yet, every day, millions of acre-feet of fresh water are dropped on the Gulf Stream from heavy rain events. My radar in Key West routinely shows thousands of square miles of ocean receiving 10-12 inches a week. One recent occurrence approximately equaled an entire month’s flow over Niagara Falls, just one event. And is it not a geostrophic current, powered by gravity? That’s what I gained from Sverdrup’s book, and I temperature wasn’t in it. Can you clarify? Thanks.
People who are familiar with paleoclimate (as opposed to models that don’t account for amplifying feedbacks) are not surprised. Starting p. 186, “THE OCEAN CONVEYOR – The real day after tomorrow”
http://www.gci.org.uk/Documents/wsav.pdf
> Dave McGinnis … is it not a geostrophic current, powered by gravity?
Only in that if you take the gravity away it stops. So does much else.
http://oceanexplorer.noaa.gov/facts/currents.html
If that’s an insufficient answer you’ll find that and much more with this:
https://www.google.com/search?q=ocean+circulation+cause
Why is nobody discussing satellite data? You are taking sparse surface measurements like HadSST 3 as gospel, yet the satellites say the opposite to surface measurements i.e. UAH / RSS have 1998 and 2010 as both being warmer than 2015.
[Response: Check out Lewandowski, he explains it beautifully and clearly. -Stefan]
The son of a friend of mine came up with Snowzilla and it’s caught on a little. Handy moniker if you don’t like the others.
I think you need to be very careful to distinguish between transient conditions and equilibrium conditions. While there is ample evidence of increasing fresh water contribution from melting glaciers and of an AMOC slow down since the 1930s the cold spot intensification last winter and this winter could also be caused by the extraordinarily intense low pressure areas that have slammed this region since last February and the intensification and northeastwards displacement of the subtropical Bermuda/Azores high.
If the recent intensification of the cool spot were caused by a recent AMOC slowdown you would expect to see warming of intermediate waters under a cool fresh water surface layer. That’s exactly what we see in seas around Antarctica. However, Mercator Ocean shows that the intermediate waters have cooled under the cool spot. Perhaps you are aware of issues with Mercator Ocean’s models that I don’t know about. I’m just a geochemist, after all.
Then how do you explain the gravity/sea surface height data?
http://bulletin.aviso.oceanobs.com/html/produits/aviso/welcome_uk.php3
The low sea surface heights above the cold blob are consistent with the Mercator Ocean profile, namely the water in that region is cold from top to bottom. The sea surface height map is consistent with active deep convection in the winters of 2015 and 2016.
Again, I think there is incontrovertible evidence that the AMOC slowed down after the mid 90’s when the intense storms and a strongly positive North Atlantic Oscillation led to the strongest AMOC in decades. The slow down after 1995 shows up in the Florida current cable data and other measures of Gulf Stream northwards transport. However, the cable data do not show a slowdown last year or this year.
I ask you these questions in hope of some resolution of the apparent inconsistencies. I blog about these matters over at Dailykos and I don’t want to be making claims that aren’t correct.
What I suspect has happened is that the winds and storms of the past 2 years have driven very cold relatively fresh water out of the Canadian Arctic into the Labrador sea. What I see looking at Mercator Ocean is that the volume of Labrador sea water has expanded and the volume of Mediterranean overflow water at 1000 meters has apparently retreated. Water temperatures have dropped and freshened at 1000 meters in the subpolar gyre.
But my impressions could be wrong. I’m trained in geology, geochemistry and geophysics, not oceanography. I appreciate how difficult the interactions between the weather and the ocean dynamics is. Perhaps you can give me an explanation that better explains the data.
Thank You,
George Birchard,PhD who posts at Daily Kos as FishOutofWater.
Dave McGinnis @26 -“Gulf Stream … powered by gravity?”
In the overall loop, as much water comes up as goes down. Density is modulated by temperature and salinity. [see also ENSO and the Pacific warm pool] For another gravitational effect:
“It has been shown that in the long-term equilibrium the strength of the thermohaline circulation in models depends on the turbulent mixing coefficient [7], and that the energy required for this turbulent mixing comes to a large extent from the moon via tidal currents ([8]).”
from http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html
hmmm there’s that name Stefan again….
Concerning satellite data (re 29): In addition to explanations by Lewandowski on uncertainties in satellite data, there are also (possible) physical explanations:
1. The time lag of El Niño impacts on global temperature in the lower troposphere is somewhat longer than at the surface (about 5 months vs. about 3 months) which means, that more of the strong El Niño effect will show up only in 2016
2. The impact of El Niño in the lower troposphere is stronger than at the surface. Since most of the effect of the current El Niño will be in 2016, the years 1998 and 2010 – both including the full effect of the preceding El Niño – are still warmer than 2015 which includes only the effect of the weak El Niño conditions from the 2014/2015 winter. Just wait for next year.
3. Warming of global surface temperatures is strongly influenced by the warming in the Arctic. This excess warming in the Arctic decreases rather rapidly with height and therefore is less reflected in the troposphere. This might also lead to a weaker warming trend in the (lower) troposphere data.
AGU has opened access to it’s articles that aren’t recent. I may have found a good answer for the apparent conflicts between data sets by reviewing the Zhang 2008 article. There’s a lag time of several years. Thus the lowest SSH and coldest temperatures may be seen just as deep convection begins to recover. The AMOC weakness we are seeing today is reflective of what was happening in the deep ocean several years ago. That fits the pattern of brief Arctic sea ice recovery in 2013 & 2014 and makes sense of the temperature profile at depth in the subpolar gyre.
“9] The weakening of the AMOC during the 70–80’s inferred from the observed Tsub PC1 (Figure 2c) lagged the observed reductions of Labrador Sea deep convection induced by Great Salinity Anomalies events at the early 70’s and 80’s [Dickson et al., 1988; Curry et al., 1998] by several years. During the recent decade, the peak of the AMOC at 1998 inferred from observed PC1s of Tsub and SSH (Figure 2c) lags the observed peak of Labrador Sea deep convection around 1994 [Yashayaev et al., 2007] by several years. The above lags are consistent with the advection time scale of the deep current from the Labrador Sea to the interior North Atlantic [Yashayaev et al., 2007]. The very recent peak of the AMOC at 2003 inferred from observed Tsub PC1 and SSH PC1 (Figure 2c) might be due to the strengthening of Nordic Sea deep convection several years before, consistent with the observed peak of Faroe Bank Channel overflow from the Nordic Sea into the Atlantic at 2003 [Steffen et al., 2008]. This Faroe Bank Channel overflow reflects Nordic Sea deep convection strength several years before. A recent modeling study [Hawkins and Sutton, 2007] also shows that changes in the Nordic Sea deep convection leads AMOC variations by a few years. Changes in the Nordic Sea deep convection could also be very important for AMOC variations. The observed SSH PC1 suggests that the AMOC has declined from its peak at 2003 during the last few years (Figure 2c).”
“… -check out the paper! ” said Prof. Rahmstorf. That was very good advice, as i discovered over the last couple days, when i finally found the time to read Dima and Lohmann. I highly recommend it.
I have a question. There should be a salinity fingerprint also in the modes A and G in Dima(2010), is there any work on that ?
sidd
http://www.sciencedirect.com/science/article/pii/S246801331500008X
“As a rebuttal of the recent Rahmstorf et al. in which the authors used proxy reconstructions and models to claim that the AMOC strength had a significant decline in the late 20th century that was unprecedented over the last millennium, the proposed coupled lines of evidence, the lack of trends in the direct AMOC observations at 41 °N over the last 10 years of Willis , the lack of trend in the SSH-only reconstruction of AMOC strength at 41 °N of Willis , and our own reconstruction based on data from two tide gauges as a proxy, rather suggest the significant stability of the AMOC merely subject to significant seasonal, inter-annual and multi-decadal variability.”
Well, well,
[Response: I’m afraid, it’s more like ‘not so well’. See Stefan’s commentary above -mike]
You left off the rest, doik:
Didn’t they get that backward? I don’t see the Rahmstorf et al. paper claiming to prove anything is, er, settled about the AMOC.
Rahmstorf et al. says that what is clearly observed — the long term trend in temperatures — can be explained by modeling what would happen _given_ changes in the AMOC.
If trend in observed temperatures — which is pretty damned clear — is happening and the AMOC isn’t changing, then we’d look for another explanation.
The Parker and Ollier paper says (amateur reading here from the abstract)
— take a different set of studies about the AMOC — “direct observations” and “SSH-only reconstruction” and “two tide gauges” — and calculate the variability (noise), and the variability is large enough that statistically they can’t detect the likelihood of a trend either up or down.
That may or may not be what the actual paper says. I’ll await Tamino’s or another statistician’s look at the calculation.
But I have to wonder about the data sources. Two tide gauges?
Seems to me they’re not arguing against Rahmstorf et al., who say that if a change in the AMOC is happening, such a change — as modeled — would explain the observed temperature patterns.
Something else might also explain the observed change in the temperature patterns.
Seems to me Parker and Ollier must also be arguing elsewhere with other atuhors of other studies _of_ the AMOC, about their data. Anyone seen such?
Or maybe I’m entirely off the mark here, of course.
I await correction, gladly.
[Response: You are right Hank. The authors claim to see variability at all times scales, including multidecadal, but no trend – from which they conclude the AMOC is stable. This is odd, because they detrended the two tide gauge time series that they used, thus eliminating any trend from their index from the start.
This is not so surprising once you know a bit of the background of Albert Parker (alias Alberto Boretti – he has at times even submitted nearly identical papers at the same time to two different journals under the two different names). He is a combustion engine expert from Australia. Quite a number of climate journals have rejected his manuscripts on tide gauge data because of their fundamentally flawed analysis, so Parker often tries to publish in non-climate journals (as again in this case).
A story of one such paper that slipped by the review is told by John Hunter: http://theconversation.edu.au/peer-review-isnt-perfect-and-the-media-doesnt-always-help-11318
Another article worth reading on an Albert Parker publication is this one by Tamino, where he shows how Parker just makes up things:
https://tamino.wordpress.com/2014/02/13/making-up-stuff/
Also worth reading: http://www.crikey.com.au/2013/12/03/dangerous-rubbish-afr-letters-ed-lashed-for-contrarian-climate-paper/ where a co-author of another Parker paper is quoted as saying:
Parker’s co-author on this new article apparently is the long-retired Geologist Cliff Ollier, who in the past has written things like:
Thorough debunkings of Parker/Boretti’s unscientific approach in the peer-reviewed literature are found e.g. here:
http://staff.acecrc.org.au/~johunter/hunter_et_al_2013_print.pdf
http://staff.acecrc.org.au/~johunter/01-Hunter.pdf
http://staff.acecrc.org.au/~johunter/final_print_version.pdf
http://link.springer.com/article/10.1007%2Fs00382-014-2224-3
I don’t intend to waste my time responding to this latest work, riddled with errors and misrepresentations.
-stefan]
Might’ve known. I looked for references to this and right on the first page it’s very popular at the usual sites frequented by those who like that sort of thing. Hey doik, where’d you come across it?
Hank and Stefan,
This was a little bit irony, i found this “Paper” very amusing, because it want show that Rahmstorf et al. are wrong and do this with 2x tide gauges which represent more the subtropical overturning not the subpolar overturning or the Gyre itself. Here the Connection between subpolar and suptropical, they totally miss what Rahmstorf et al. had looking for. And some People are fail to get this.
They argue then, the “cold spot” is more due AMO (detrend) which is the next Joke and for this, in my opinion, the only Way for a Rebuttal on Rahmstorf et. al is to show. 1) “Cold Spot” is mainly driven by Wind-Forcing over the SPG(Subpolar-Gyre),which is deepens the mixed Layer and cause upwelling of colder Water. 2) That this is not related to Global or NH-Warming.
My motivation to post this Paper was to see the response by someone with expertise in this field and i used “Well well” as a signal that i belive would cause more impact to some people