A few weeks ago, we’ve argued in a paper in Nature that the Atlantic overturning circulation (sometimes popularly dubbed the Gulf Stream System) has weakened significantly since the late 19th Century, with most of the decline happening since the mid-20th Century. We have since received much praise for our study from colleagues around the world (thanks for that). But there were also some questions and criticisms in the media, so I’d like to present a forum here for discussing these questions and hope that others (particularly those with a different view) will weigh in in the comments section below.
Exhibit #1, and the prime observational finding, is a long-term cooling trend in the subpolar Atlantic – the only region in the world which has cooled while the rest of the planet has warmed. This ‘cold blob’ or ‘warming hole’ has been shown in IPCC reports since the 3rd assessment of 2001; it is shown in Fig. 1 in a version from the last (5th) IPCC report. In fact it is Figure 1 of the Summary for Policy Makers there – you can’t get more prominent than that.
Fig. 1 Observed temperature trends since the beginning of the 20th Century (Figure SPM1 of the last IPCC report).
I think there is a consensus that this is a real phenomenon and can’t be explained away as a data problem. According to NOAA, 2015 was the coldest year in this region since record-keeping began in 1880, while it was the hottest year globally. The key question thus is: what explains this cold blob?
In 2010, my colleagues Dima and Lohmann from Bremen were the first (as far as I know – let me know if you find an earlier source) to suggest, using sea surface temperature (SST) pattern analyses, that the cold blob is a tell-tale sign of a weakening AMOC. They wrote that
“the decreasing trend over the last seven decades is associated to the weakening of the conveyor, possibly in response to increased CO2 concentrations in the atmosphere”
(with ‘conveyor’ they refer to the AMOC). One of several arguments for this was the strong anti-correlation pattern between north and south Atlantic which they found using canonical correlation analysis and which is the well-known see-saw effect of AMOC changes.
I have since become convinced that Dima and Lohman were right. Let me list my main arguments upfront before discussing them further.
- The cold blob is a prediction come true. Climate models have long predicted that such a warming hole would appear in the subpolar Atlantic in response to global warming, due to an AMOC slowdown. This is seen e.g. in the IPCC model projections.
- There is no other convincing explanation for the cold blob. There is strong evidence that it is neither driven by internal atmospheric variability (such as the North Atlantic Oscillation, NAO) nor by aerosol forcing.
- A range of different data sets and analyses suggest a long-term AMOC slowdown.
- Claims that the slowdown is contradicted by current measurements generally turn out to be false. Such claims have presented apples-to-oranges comparisons. To the contrary, what we know from other sources about the AMOC evolution is largely consistent with the AMOC reconstruction we presented in Nature.
Let us look at these four points in turn.
A climate prediction come true
The following graph shows climate projections graph from the last IPCC report.
Fig. 2 Global warming from the late 20th Century to the late 21st Century (average over 32 models, RCP2.6 scenario) – Figure SPM8a of the IPCC AR5.
The IPCC writes that “hatching indicates regions where the multi-model mean is small compared to natural internal variability (i.e., less than one standard deviation of natural internal variability in 20-year means.)” The subpolar North Atlantic stands out as the only region lacking significant predicted warming even by the late 21st Century. The 4th IPCC report included a similar graph (Fig. TS28).
In our paper we have analysed the ‘historic’ runs of the CMIP5 climate models (i.e. those from preindustrial condition to the present) and found that the observed ‘cold blob’ in this region is consistent with what the models predicted, with the amount of cooling in the models depending mainly on how much the AMOC declines (see below). In the mean of the 13 models we examined (Fig. 5 of our paper), the downward trend of the AMOC index is -0.33 °C per century, in the observations we found -0.44 °C per century. (Our AMOC index simply consists of the difference between the surface temperatures of the subpolar Atlantic and the global ocean). The models on average thus predicted three quarters of the decline that the observational data indicate. (In fact most models cluster around the observed decline, but three models with almost zero AMOC decline cause the underestimation in the mean.)
Is there an alternative explanation?
If the ocean temperature in any region changes, this can only be due to a change in heat supply or loss. That can either be a change in heat flow via ocean currents or through the sea surface. Thus the subpolar Atlantic can either have cooled because the ocean currents are bringing less heat into this region, or alternatively because more heat is being lost to the atmosphere. So how do we know which of these two it is?
First, we can analyze the heat flux from ocean to atmosphere, which can be calculated with standard formula from the sea surface temperature and weather data. Halldór Björnsson of the Icelandic weather service has done this and presented the results at the Arctic Circle conference 2016 (they are not published yet). He showed that the short-term temperature fluctuations from year to year correlate with the heat exchange through the sea surface, but that this does not explain the longer-term development of the ‘cold blob’ over decades. His conclusion slide stated:
Surface heat fluxes did not cause the long term changes and are only implicated in the SST variations in the last two decades. Long term variations are likely to be oceanic transport but not due to local atmospheric forcing.
That’s exactly what one expects. Weather dominates the short-term fluctuations, but the ocean currents dominate the long-term development because of the longer response time scale and “memory” of the ocean.
Nevertheless some have suggested that the main mode of atmospheric variability in the north Atlantic, the North Atlantic Oscillation or NAO, might have caused the “cold blob”. In our paper we present a standard lagged correlation analysis of the NAO with the “cold blob” temperature (in form of our AMOC index). The result: there is indeed a significant correlation of the NAO with subpolar Atlantic surface temperatures. But on the longer time scales of interest to us (for 20-year smoothed data), changes in the sea surface temperature lead the NAO changes by three years. We conclude that changes in sea surface temperatures cause the changes in NAO and not vice versa. (And we’re certainly not the first to come to this conclusion.)
And a third point: in summer, the effect of heat flow through the sea surface should dominate, in winter the effect of ocean currents. That is because the well-mixed surface layer of the ocean is thin, so only the uppermost part of the ocean heat transport gets to affect the surface temperature. But the thin surface layer still feels the full brunt of atmospheric changes, and even stronger than in winter, because the thermal inertia of the thin summer surface layer is small. In our paper we analysed the seasonal cycle of the temperature changes in the subpolar Atlantic. The cooling in the “cold blob” is most pronounced in winter – both in the climate model (where we know it’s due to an AMOC slowdown) and in the observations. That yet again suggests the ‘cold blob’ is driven from the ocean and not the atmosphere.
There is another well-known mode of Atlantic temperature variability known as AMO, which correlates strongly with our AMOC index. Its established standard explanation in the scientific literature is… variations in the AMOC. (The NAO and AMO connections are discussed in more detail in the Extended Data section of our paper.)
There may be the possibility that some ocean heat transport change other than an AMOC change could be responsible for the ‘cold blob’ in the subpolar Atlantic, and I wouldn’t argue that we understand the ocean current changes in detail. But if you take a ‘big picture’ view, it is a fact that the AMOC is the dominant mechanism of heat transport into the high-latitude Atlantic, and the region that has cooled is exactly the region that cools in climate models when you slow down the AMOC. We have analysed the ensemble of CMIP5 “historic” model simulations for the past climate change from 1870 to 2016. For each of these model runs, we computed the AMOC slowdown over this time as diagnosed by our AMOC index (i.e. based on subpolar ocean surface temperatures) as well as the actual AMOC slowdown (which we know in the models, unlike in the real world.) The two correlate with a correlation coefficient R=0.95. Thus across the different models, differences in the amount of AMOC slowdown nearly completely explain the differences in subpolar Atlantic temperatures. If you doubt that what the temperatures in the Atlantic are telling us is a story of a slowing AMOC, you doubt not only that the high-resolution CM2.6 climate model is correct, but also the entire CMIP5 model ensemble.
A range of different data sets and analyses suggest a long-term AMOC slowdown
A number of different SST data sets and analyses support the idea of the AMOC slowdown. That is not just the existence of the subpolar cooling trend in the instrumental SST data. It is the cross-correlation with the South Atlantic performed by Dima and Lohmann. It is the fact that land-based proxy data for surface temperature suggest the cold blob is unprecedented for over a millennium. It is the exceptional SST warming off the North American coast, an expected dynamical effect of an AMOC slowdown, and strong warming off the west coast of southern Africa (see Fig. 1 in my previous post).
In addition we have the conclusion by Kanzow et al. from hydrographic sections that the AMOC has weakened by ~ 10% since the 1950s (see below). And the Nitrogen-15 data of Sherwood et al. indicating a water mass change that matches what is predicted by the CM2.6 model for an AMOC slowdown. And the subsurface Atlantic temperature proxy data published recently by Thornalley et al. Plus there is work suggesting a weakening open-ocean convection. And finally, our time evolution of the AMOC that we proposed based on our AMOC index, i.e. based on the temperatures in the cold blob region, for the past decades matches evidence from ocean reanalysis and the RAPID project. Some of these other data are shown together with our AMOC index below (for more discussion of this, see my previous post).
Fig. 3 Time evolution of the Atlantic overturning circulation reconstructed from different data types since 1700. The scales on the left and right indicate the units of the different data types. The lighter blue curve was shifted to the right by 12 years since Thornalley found the best correlation with temperature with this lag. Our index is the dark blue line starting in 1870. Graph: Levke Caesar.
Do measurements contradict our reconstruction?
Measuring the AMOC at a particular latitude in principle requires measuring a cross-section across the entire Atlantic, from surface to bottom. There are only two data sets that aspire to measure AMOC changes in this way. First, the RAPID project which has deployed 226 moored measuring instruments at 26.5 ° North for that purpose since 2004. It shows a downward trend since then, which closely matches what we find with our temperature-based AMOC index. Second is the work by Kanzow et al. (2010) using results of five research expeditions across the Atlantic between 1957 and 2004, correcting an earlier paper by Bryden et al. for seasonal effects and finding a roughly 10% decline over this period (in terms of the linear trend of these five data points).
Some other measurements cover parts of the overturning circulation, and generally for short periods only. For 1994-2013, Rossby et al. (2013) – at the Oleander line between 32° and 40° North – found a decrease in the upper 2000m transport of the Gulf Stream by 0.8 Sverdrup (a Sverdrup is a flow of a million cubic meters per second). It is important to realize that the AMOC is not the same as the Gulf Stream. The latter, as measured by Rossby, has a volume flow of ~90 Sverdrup, while the AMOC has a volume flow of only 15-20 Sverdrup. While the upper northward branch of the AMOC does flow via the Gulf Stream, it thus only contributes about one fifth to the Gulf Stream flow. Any change in Gulf Stream strength could thus be due to a change in the other 80% of Gulf Stream flow, which are wind-driven. The AMOC does however provide the major northward heat transport which affects the northern Atlantic climate, because its return flow is cold and deep. Most of the Gulf Stream flow, in contrast, returns toward the south near the sea surface at a similar temperature as it flowed north, thus leaving little heat behind in the north.
Likewise for 1994-2013, Roessler et al. (2015) found an increase of 1.6 Sv in the transport of the North Atlantic Current between 47° and 53° North. This is a current with a mean transport of ~27 Sverdrup, 60% of which is subtropical waters (i.e., stemming from the south via the Gulf Stream). For this period, our reconstruction yields an AMOC increase by 1.3 Sv.
For 1994-2009, using sea-level data, Willis et al. (2010) reconstructed an increase in the upper AMOC limb at 41°N by 2.8 Sv. For this period, our reconstruction yields an AMOC increase by 2.1 Sv.
Finally, the MOVE project measures the deep southward flow at 15° North. This is a flow of ~20 Sverdrup which can be considered the sum of the north Atlantic overturning circulation plus a small component of returning Antarctic Bottom Water (see Fig. 1 in Send et al. 2011). The following graph shows all these measurements together with our own AMOC index (Caesar et al 2018).
Fig 4. Our AMOC index in black, compared to five different measurement series related more or less strongly to the AMOC. The dashed and dotted linear trends of our index can be directly compared to the linear trends over corresponding data intervals. The solid black line shows our standard smoothed index as shown in our paper and in Fig. 3. Graph by Levke Caesar.
First of all, it is clear that these data contain a lot of year-to-year variability – which doesn’t correlate between the different measurements and for our purposes is just ‘noise’ and not a climate signal. That is why for our index we generally only consider the long-term (multidecadal) changes in SST to reflect changes in the AMOC. Thus, we need to look at the trend lines in Fig. 4.
Given that even these trends cover short periods of noisy data sets and thus are sensitive to the exact start and end years, and that lags between the various parts of the system may be expected, all these trends are surprisingly consistent! At least I don’t see any significant differences or inconsistencies between these various trends. Generally, the earlier trends in the left part of the graph are upward and the later trends going up to the present are downward. That is fully consistent with our reconstruction showing a low around 1990, an AMOC increase up the early 2000s and then a decline up to the present (compare Fig. 3).
Claims that any of these measurements are at odds with our index or even disprove the long-term AMOC decline are thus baseless (and thus rightly fit into Breitbart News where they were raised by the notorious James Delingpole).
One interesting question for further research is how the AMOC in the Atlantic is linked to the exchange with the Nordic Seas across a line between Greenland, Iceland and Scotland. In our 2015 paper we showed a model result suggesting an anti-correlation of these overflows with the AMOC, and our new paper suggests a similar thing: a warm anomaly off Norway coinciding with the cold anomaly in the subpolar Atlantic, both in the high-resolution CM2.6 model and the observations.
So, while there is obviously the need to understand the ocean circulation changes in the North Atlantic in more detail, I personally have no more doubts that the conspicuous ‘cold blob’ in the subpolar Atlantic is indeed due to a long-term decline of the northward heat transport by the AMOC. If you still have doubts, we’d love to hear your arguments!
221 Responses to "If you doubt that the AMOC has weakened, read this"
Kevin McKinney says
Yes, I saw that SKS article in my search. However, I didn’t consider it relevant, because the delay it is talking about is the delay between CO2 rise and warming of the entire Earth system–that is, both atmospheric and sea surface temperatures. Unless I’m gravely mistaken, there’s not a word in there suggesting the existence of a decadal lag between atmospheric and oceanic temperature responses.
So your statement that “Moreover, as we know, there is a decadal time lag between atmospheric temperatures and ocean temperatures…” should read “Moreover, as we know, there is a decadal time lag between atmospheric GHG increase and ocean temperature rise…”
I think we need to be careful in thinking about that fact, though. If we aren’t clear about what is meant by ‘lag’, we may start thinking that nothing happens to SSTs for decades after GHG concentrations rise. That isn’t the case, of course; the “lag” is the lag in reaching a new equilibrium. Basically, the lag isn’t a lag in the onset of SST warming; it’s a lag in the completion of SST warming. (Of course, all that is theory, albeit well-supported theory; in the real world, GHGs haven’t stopped increasing yet, which is a pre-condition for equilibrating, obviously.)
There is a difference between oceanic and atmospheric response amplitudes, though. That’s well-known, and also visible in the graph I cobbled up. That, too, is down to the thermal inertia of the oceans. Remember the very well-known proposition that over 90% of the ‘greenhouse energy’ added to the Earth system is absorbed by the oceans. For instance, this discussion:
“Humans thus, living at the interface of the land, ocean and atmosphere, only feel a sliver of the true warming cost of fossil fuel emissions.”
After researching several papers, the answer I found is “yes”, the sst in the atlantic south of the cold blob increases (dipole), bringing increasing sst via the gulf stream all along to the east coast of the US and to western europe. The gulf stream heats up under an amoc slowdown scenario, bringing hotter summers to the US east coast and Europe and it will get significantly drier in these regions (no “wetter regions will become wetter and drier regions will become drier”). But what about winter? Most model projections show colder winters in Europe, but winters are getting hotter and hotter recently, why is it? The last couple of years the weather pattern changed in winter, weather resiliently came in from the western gulfstream or even from the mediterranean south, we lacked inflow from northern and eastern weather, thus the winters got warmer and warmer. Why is it? Changes in the jetstream?
D Trossman says
Great post and discussion. There is yet another possible mechanism that hasn’t been isolated observationally (yet, as far as I’m aware), but could become important in the decades to come for the warming hole/cold blob just south of Greenland. I’d describe it as follows. The declining AMOC will lead to an increased meridional SST gradient in the subpolar North Atlantic Ocean, as you and others (e.g., Winton, 2003) have argued. This increased gradient leads to enhanced storm tracks (Woollings et al., 2012), which results in increased downward vertical velocity anomalies equatorward of the jet and enhanced boundary layer inversion strength (Grise and Medeiros, 2016). The increased vertical stability of the lower troposphere reduces the entrainment of dry upper tropospheric air into the lower troposphere and increases cloud coverage (Klein and Hartmann, 1993; Wood and Bretherton, 2006). The increased “low cloud” coverage then cools the sea surface.
This is shameless self-advertising on my part, but if you look at Figures 4 and S1 in Trossman et al. (2016: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL067931), you’ll see that holding the cloud coverage, liquid water content, and ice water content to be the same as they were in the simulation’s pre-industrial times and/or holding the resolved ocean velocities to be the same as they were in the simulation’s pre-industrial times makes the warming hole/cold blob virtually disappear. There is still a little bit of a cooling effect in the SST when only the clouds are held “fixed” (albeit, still time-variable) in this sense, but the cooling is much reduced when the clouds and/or ocean circulation aren’t allow to respond to the 1% to doubling of carbon dioxide scenario in the CM2Mc (coarse resolution version of GFDL’s ESM2M modeling system) model. In other words, only when we allowed for the fully dynamic interaction between the ocean circulation and clouds did the model show a realistic-looking warming hole/cold blob. Any thoughts on this would be much appreciated.
Kevin McKinney @41
Just to add a bit.
When warming is discussed, the reference is the global mean surface temperature which represents the air temperature near the surface of the planet. On land, this is based on the thermometer record. Over the ocean, there are no thermometers so sea surface water temperatures historically measured by ships are used as a proxy. Sea surface water temperatures and land temperatures have risen and fallen pretty much in lockstep. There is NO lag.
Furthermore Victor says: “We cannot ignore, moreover, the time it would take for any atmospheric warming to be transferred to the oceans.” This of course is false, the atmosphere is mostly warmed by the surface, both land and sea, not visa versa. Both surfaces are warmed by solar irradiation along with back radiation. However, that is not to say heat from the atmosphere cannot flow back, it does, the rate of this continuous exchange between the atmosphere and oceans causes natural variability.
The ocean has a huge capacity to store heat due to the significant heat capacity of water and the enormous mass of the oceans. Due to mixing, some of the surface heat gets transferred to the depths over time. That is the delay in the SKS article. However, it is the SURFACE temperatures that drive the THC along with salinity not that heat at the depths.
How do you then explain that the arctic ocean gets ‘crazily’ warmer ?
CO2 above the arctic ? (it is a joke here about CO2…)
[Response: I mention the anticorrelation between Arctic Ocean and subpolar Atlantic in my article. One explanation can be found in the paper by Jungclaus et al.: a weaker AMOC leads to a stronger subpolar gyre which brings more relatively warm Atlantic waters up into the Arctic. -Stefan]
Hank Roberts says
Just to try to resolve that tangent earlier:
42 nigelj says:
nj: Victor @40, I think you are mistaken about the timing of the AMOC changes. Stefan has already said at post 17 above the significant slowdown in the AMOC starts about 1970, and you can see it in the graph in the article. This relates closely enough to when global temperatures started warming significantly.
v: Yes, timing is key. But Stefan keeps changing the goalposts in that respect, no? First he says the system “has weakened significantly since the late 19th Century,” but then immediately qualifies that by adding “with most of the decline happening since the mid-20th Century.” 1970 isn’t even mentioned in the post appearing above. He points to that date only in response to the inconsistency I noted in a recent comment.
So which is it? If it began in the late 19th century, then it obviously has nothing to do with CO2 emissions. And if most of the decline can be dated to the mid-20th century then once again it’s very difficult to associate it with warming due to fossil fuel emissions, since there was no warming at all mid-century. And if he prefers to fall back on 1970, then yet again I see no warming at or even near that date. Land-sea temperatures didn’t begin to heat up in any significant manner until the late 1970’s. Is that close enough? Well, for one thing that was the period when things BEGAN to heat up — the actually heating could not have had much of an effect until several years later. I have no reason to dispute Rahmstorf’s hypothesis regarding the weakening of AMOC, though I’m obviously not qualified to form an opinion on that matter, but the evidence on its face does NOT support AGW as a significant cause. Clearly, if the process began in the late 19th century there must be some other cause.
nj: Sea surface temperatures respond quickly to atmospheric warming, but oceans respond more slowly at full depth, so yes there is a delay there. Its surface temperatures that are most relevant to this issue at hand anyway.
V: Yes, since the gulf stream operates on the ocean surface you do have a point. Nevertheless, there would have to be some delay involved, since water heats more slowly than air. And also, as stated above, it’s a mistake to attribute the effects of any warming trend to the earliest manifestations of that trend. It obviously takes time not only for water to heat up but also for atmospheric temperatures to rise after a long (40 year) period of relative stasis. It looks to me like Stefan’s timing is off as far as human influence is concerned, though the rest of his theory might well be perfectly accurate.
The sea surface heats at a similar rate as the land surface through solar insolation. It is the sea surface and land surface that in turn heats the air. If there was a delay, it would be that of the atmospheric warming.
barn E. rubble says
RE: “So, while there is obviously the need to understand the ocean circulation changes in the North Atlantic in more detail, I personally have no more doubts that the conspicuous ‘cold blob’ in the subpolar Atlantic is indeed due to a long-term decline of the northward heat transport by the AMOC.”
Just wondering if it’s just a coincidence that Newfoundland tour operators have noticed a major drop in icebergs this Spring? It’s my understanding the Irminger Current runs north, while the East Greenland Current runs south.
Hank Roberts says
Victor, aren’t you making stuff up again?
Or can you cite some source?
Try here: https://www.acs.org/content/acs/en/climatescience/greenhousegases/industrialrevolution.html
“Yes, timing is key. But Stefan keeps changing the goalposts in that respect, no?”
I don’t think he has moved any goalposts. I think he was arguably rather loose or too approximate saying most of the decline happened after the middle of the 20th century when it was after 1970, but his intent was obviously just a general and approximate description, and the information was there in the data in graph and the data is obviously the most important thing.
I have previously explained why I think there would be a difference of 5 – 10 years between the significant slowdown of the amoc in the 1970’s and temperatures.
“Nevertheless, there would have to be some delay involved, since water heats more slowly than air. ”
Probably days, weeks, months. Not ten years unless you are talking about the deepest parts of the oceans. Notice how quickly the ocean heats during hot weather if you are swimming in summer.
And I dont understand your point. Its clear in the graph I posted the oceans were warming from approximately 1975 and this is close enough to when the amoc started significantly slowing.
Just as a general note, I mostly dont care about small discepencies in this climate issue because theres so much ‘noise’ from short term natural factors that they mean nothing. I thought you had identified a larger discrpepancy between 1950 and the 1970s, but its not the case and was just that the articles description was a little bit too approximate. It had me fooled initially as well, until I looked hard at the graph.
I’m not a climate scientist, however I see that CC Holey has now posted comments saying much the same as what I did.
Lets not go on about it because as far as Im concerned these issues are settled. Im replying mainly because I was initially wondering about the time gap as well, until I stared hard at the graph, so it was slightly confusing.
Al Bundy says
Posting for points instead of mutual understanding is putrid. Stefan’s point was easy to discern given the three statements combined with the graph. Then he went the extra mile by answering several comments.
Grow up. Stupidity is not a bad trait. Deliberate stupidity is. Stop throwing airballs on purpose. Folks get tired of having to retrieve them
Re. icebergs in Newfoundland. I sail in Conception Bay Newfoundland near St. John’s. There is indeed a shortage of bergs this year. Over the past 37 years there has been an easily-observed general decline in the amount of pack ice and icebergs making it this far south in spring for whatever reasons. Factors this year would include a very strange spring here w/o the usual long term pattern of rain, drizzle, fog, and NE winds. Rather, it has been cool and sunny with daily strong, even near gale, souwesterlies all spring. Referring to today’s ice map as a result of the wind/weather you can see that even in Labrador there is no shore ice (http://ice-glaces.ec.gc.ca/prods/WIS27/20180530180000_WIS27_0010056019.pdf) and the ice pack as a whole is far to the north of the island and most of the bergs (which survive longer than sea ice, of course) will be found out to sea to the east. I have seen only 5 bergs, all on the Atlantic side east of St. John’s all well out to sea. None have been seen inside Conception Bay. See https://icebergfinder.com/ for information and integrated sightings/pics on all observed bergs here.
I suspect all that the extra heat in the eastern Canadian Arctic in late winter/early spring may have had an effect as well.
Kevin McKinney says
You’re right, but Victor isn’t going to stop ‘throwing airballs,’ if history is any guide. He’s long since made up his mind that AGW isn’t real, and he’s willing to ‘die’ on any random rhetorical ‘hill’ that is more or less relevant to demonstrating that. It isn’t about learning anything. Haters hate, they say; but deniers most definitely deny. That’s the emotional bedrock reality behind “If it began in the late 19th century, then it obviously has nothing to do with CO2 emissions.”
It’s wrong, and that’s been pointed out in excruciating detail by me and many others, in various ingenious ways. It didn’t make a difference then, and it won’t in the future either, unless lightning strikes from the heavens or some such.
Well, it is rather a decline in the subpolar gyre (SPG), not a stronger subpolar gyre, that causes more relatively warm Atlantic waters up into the Arctic:
The SPG “declined after the mid-1990s (Häkkinen and Rhines, 2004). This resulted in a sudden warming and salinification in the subpolar North Atlantic due to increased northward intrusion of relatively warm and saline subtropical water from the eastern Atlantic (Bersch et al., 1999; Hátún et al., 2005; Robson et al., 2012).” (Hátún and al.)
Presently, the observed cold blob is due to an “inflation” of the subpolar gyre (SPG) associated with an increase in deep convection into the Labrador and Irminger Seas .
More melting of ice causes a stronger Eastern Greenland current (cold flux), and thus an increase in deep convection and a stronger subpolar gyre, giving rise to the observed cold blob.
However, “the North Atlantic MOC is not largely impacted by deep convection in the Labrador Sea”(Pickart and al), and thus it is not significantly affected by the increased cold flux of the Eastern Greenland current or the inflation of the cold blob.
I think the AMOC is just going around, it does not get weaker: some observational evidences show that despite the cold blob, strong warming anomalies have been traced in the Eurasian Basin of the Arctic Ocean (Polyakov and al.), indicating that the AMOC is still there and well alive, and is fed with pulse-like signatures, suggesting abrupt, anthropic causes, like tropical deforestation causing evaporation of land water on large surfaces and feeding in return the ocean and thus the AMOC.
[Response: Please note a key point of my article: be careful about what time interval you are talking about. So in 2004, Häkkinen and Rhines conclude that the SPG has weakened since the mid 90s. That is an interval over which in our reconstruction the AMOC has strengthened, and is thus completely consistent with the finding of Jungclaus of an anti-correlation between the strength of SPG and AMOC. -Stefan]
We Don’t Have Time
We are beyond the question of whether climate change and overuse of ecological resources lead to catastrophe or not.
The question is about the proportion of the catastrophe, and whether or not it will lead to a complete breakdown of our societies.
The scientific community has issued a unanimous warning to humanity about the dangers of climate change. To those who deny this warning, we say: To include you in the conversation would be a waste of time. Every hour spent debating a science denier is an hour less spent finding solutions to our problems.
We Don’t Have Time to wait, we must act. NOW.
I should have mentioned also that for the first time in the 37 years I’ve lived here I saw whales and gannets feeding near shore deep within an arm of the bay in May. Usually the bay doesn’t really come alive until much later in June. The weather this year is simply different this year. Don’t know about the climate, of course.
#61 nigelj: “I think he was arguably rather loose or too approximate saying most of the decline happened after the middle of the 20th century when it was after 1970, but his intent was obviously just a general and approximate description, and the information was there in the data in graph and the data is obviously the most important thing.”
V: Quite a list of excuses, nj. Why not let Stefan speak for himself? And by the way, the data does not fit the premise that temperature rise due to CO2 was responsible for the AMOC weakening, simply because there was NO such rise in temps, not in 1950 nor 1970, but beginning considerably later, around 1979. And 1979 was just the beginning — any impact from that rise would have come years later.
nj: “Its clear in the graph I posted the oceans were warming from approximately 1975 and this is close enough to when the amoc started significantly slowing.”
V: According to the same graph, air temps fell close to an all time low in 1975. And once again, you can’t assess the effect of a temperature rise based on the time it began.
From Stefan’s Nature paper: “Although long-term natural variations cannot be ruled out entirely, the AMOC decline since the 1950s is very likely to be largely anthropogenic, given that it is a feature predicted by climate models in response to rising CO2 levels.”
An assessment of CO2 levels per se is not enough to establish a meaningful correlation in this case, when a necessary third term has been omitted: the effect of CO2 on temperature. While CO2 levels did indeed begin to soar around the 1950’s, temperatures remained more or less static, only beginning to rise significantly around 1979 (NOT 1970, as implied by his Figure 6). This major discrepancy of roughly 30 years appears to represent a blind spot for Rahmstorf, not only in this instance, but also in his assessment of sea level rise, as I pointed out earlier.
Mal Adapted says
IMUMO, Mr. Bundy’s comment is exceptionally insightful. ‘Point’ is an overloaded word, however. There’s no doubt Dr. Rahmstorf, like all RC’s principal authors, writes his articles to impart a ‘point’ of deep scientific knowledge to his readers. If his responses to AGW-denialist comments are sometimes ‘pointed’, it’s presumably in response to the denier’s attempt to score ‘points’ 8^).
Commenters on RC posts, OTOH, evince a wider range of scientific understanding, and awareness of their own and others’ cognitive motivations. Again IMUMO, comments are always made to score points, their value depending on the point being made. Sometimes, narcissistic point-scoring is the commenter’s whole point (and I won’t try to refute suspicion pointed at me ;^})!
Also IMUMO, the substantive points left to make are explicitly outside RC’s mission and contributors’ expertise. Details of climate science may be scientifically interesting, but in the overriding pragmatic context the science is settled. The economic causes of AGW are also known with high confidence. The human costs of the linked weather changes are already being tabulated in money and tragedy, and are justifiably projected to mount non-linearly with fossil carbon emissions. And as cited frequently on RC, classes of relative winners and losers are identified. That last sentence explains why the problem remaining to be solved is political!
That said, RC still informs my best scientifically meta-literate understanding of the lopsided consensus of climate scientists. I’m frankly bored, however, by quibbles about some detail of climate physics. AGW’s economic bill in arrears is already being paid around the world, willy-nilly and wildly out of proportion to the payers’ contribution to the cause. Residents of developed nations aren’t exempt from payment, although not in proportion to our fossil carbon emissions either, and relatively buffered by our financial resources. The point climate realists must now make to their inattentive and/or resistant compatriots is that, implicitly agenda-driven news they hear on TV notwithstanding, the aggregate cost of global warming won’t be capped without collective action at the national level!
My own support for Carbon Fee and Dividend with Border Adjustment Tariff is no secret, but I can’t claim it’s made much political headway, and I’m quite willing to consider any potentially effective proposal made in good faith. Any attempt at deception, by disinformation professionals or disinformed, cognitively motivated volunteers, had better be good. Otherwise, assuming it passes moderation, it should be expected to provoke large heaps of exhaustively referenced scorn and derision here.
barn E. rubble says
RE: 65 jgnfld says:
31 May 2018 at 9:48 AM
“The weather this year is simply different this year. Don’t know about the climate, of course.”
Rex Murphy recently wrote about Nfld weather/climate change saying, ” ‘No two days the same’ should be the provincial motto. ‘Tomorrow will certainly be worse’ should be the followup.'”
barn E. rubble says
RE: 63 jgnfld says:
31 May 2018 at 6:42 AM
“I suspect all that the extra heat in the eastern Canadian Arctic in late winter/early spring may have had an effect as well.”
I understand how warming could increase melting/breakaway ‘bergs. I was wondering if the ‘cold blob’ &/or weakened AMOC was now connected to fewer than the ‘usual’ number of icebergs. My understanding is that the drop this spring was significant.
68 Victor says “While CO2 levels did indeed begin to soar around the 1950’s, temperatures remained more or less static, only beginning to rise significantly around 1979 (NOT 1970, as implied by his Figure 6). This major discrepancy of roughly 30 years appears to represent a blind spot for Rahmstorf, not only in this instance, but also in his assessment of sea level rise, as I pointed out earlier.”
I think I get where you’re coming from. This climate science business is extremely complicated. I know of no human capable to hold all the knowledge and variables in the space between their ears. When the scientists themselves cannot keep up with the volume of knowledge (eg Stefan noting he’ll include another ref above, and complaints by others not being properly credited) and so many arguing with each others conclusions publicly 24/7 it’s problematic. A self-appointed expert/lawerly nigelj is not going to help anyone.
The typical response is you simply need to go read the science, follow the refs of peer reviewed papers. Unfortunately that a paper has been peer-reviewed is no guarantee it’s conclusions are valid or that when a small issue in that paper is ref’d in a new paper that that is credible. Peer Reviewed doesn’t mean everything said in a paper is 100% reliably true and correct. It’s a club and you ain’t in it. :-)
Anyway the issue about the SSTs is not the whole thing about warming of the oceans. Other papers and the accepted consensus is that the heat from global warming was entering the ocean system all the time but due to it’s mass size in the 19th and 20th centuries that warming was not showing up in the very limited temperature readings done by man. Especially due to deep circulations where the heat was transported downward 24/7.
Now I don’t know if that is a valid reason that might resolve your dilemma above and I don’t know which specific papers or checked factoid in the IPPC might confirm my memory here or could enlighten you or anyone better. I do not see this as your fault as it is simply a matter of information overload on this subject, complexity, poor reporting, and many other matters. Such as many presume you do not deserve an answer and it’s all your personal fault nor failings. I don’t buy that excuse myself, but it is what it is. That’s reality. A crying shame.
The solution? I can’t see one in the foreseeable future. I see it getting much worse and no resolution of the underlying causes.
“V: Quite a list of excuses, nj. Why not let Stefan speak for himself? ”
Because you asked me for my opinion on Stefans approach and I gave it! Don’t ask things if you don’t want answers, because you are wasting everyones time.
Honestly Al Bundy has you summed up perfectly. Your rhetoric is childish points scoring and game playing, and shows no desire to learn or admit you are wrong.
“V: According to the same graph, air temps fell close to an all time low in 1975. And once again, you can’t assess the effect of a temperature rise based on the time it began.”
So what, the warming trend started from 1975 or near enough such that its pedantic nit picking to dispute it. It correlates well with the amoc slowdown. The more temperatures increased after 1975, the more it slowed down.
“An assessment of CO2 levels per se is not enough to establish a meaningful correlation in this case, ”
OT and it has been explained to you literally a dozen times that the near flat period of temperatures mid last century was due to aerosols. By analogy put a heater and air conditioner in the same room at the same time, and they cancel each other out.
I think this website gives you too much space for endless repetition. Your initial point was ok, but the rest has become just repetition and is distracting from the article. Hence I have been brief in my response.
Seems to me when we look at sea surface temperatures only, they seem to have started to rise about 1950 and certainly by 1970.
#64 Kevin McKinney says:
KM: “#62, Al– You’re right, but Victor isn’t going to stop ‘throwing airballs,’ if history is any guide. He’s long since made up his mind that AGW isn’t real, and he’s willing to ‘die’ on any random rhetorical ‘hill’ that is more or less relevant to demonstrating that. It isn’t about learning anything. Haters hate, they say; but deniers most definitely deny.”
I love it when the resident “experts” here start pontificating when at a loss for reasonable arguments. Obviously I’m not here to convince any of you — you are all hopelessly captured, victims of your own failure to think independently. What then IS the reason I’m here, you ask? Actually it has little to do with me. TRUTH WILL OUT. That’s what’s happening when I post.
KM: That’s the emotional bedrock reality behind “If it began in the late 19th century, then it obviously has nothing to do with CO2 emissions.” Care to elaborate, KM? Can you refute that statement with actual evidence?
Here’s another example of my “denialism”:
“And by the way, the data does not fit the premise that temperature rise due to CO2 was responsible for the AMOC weakening, simply because there was NO such rise in temps, not in 1950 nor 1970, but beginning considerably later, around 1979. And 1979 was just the beginning — any impact from that rise would have come years later.”
Can you drop the indignant pose for long enough to provide a rational response? And if not, why not?
“should we call out systematic misinformers like Breitbart, or just ignore them? What do other readers think?”
I would ignore naming Breitbart and Dellingpole. No need to give them name recognition, and give people information to google that will cause doubt and confusion. Just say “claims from some interested parties that these measurements…….. are thus baseless.” Its important to answer critics of course.
Mal Adapted @69 I wonder if you are confusing a fairly normal desire to be appreciated and win an intellectual debate on the facts, with the sort of small minded, personalised, points scoring, nasty game playing we see all over the net. Not referring to you of course.
Simon C says
CCHolley @ 74 – Dan Schrag gave a convincing talk over here (UK) recently, arguing that much of the “additional” variance (besides AGW and the usual background factors such as aerosols) in the global climate history could be attributed to the operation of Pacific circulatory processes, in particular the Pacific Decadal Oscillation. While it might be surprising that one ocean – even *that* ocean – could exert such a profound effect on global temperatures, it seems to work in modelling terms. So it may be that there is an additional factor to be considered which may well help to understand the convolutions of the climate record. cf Decadal changes in South Pacific sea surface temperatures and the relationship to the Pacific decadal oscillation and upper ocean heat content; Linsley, Wu, Dassié, Schrag Geophys Res Letters 2015. Part of the AGW signal may have been obscured by Pacific circulation, so it might not be so obvious when it “kicks in” for the first time.
Igor Yashayaev says
Cooling of the surface (let’s say somewhere is subpolar North Atlantic in winter) increases water density and causes the cooled surface water to sink. When the surface gets even colder there is more sinking likely to occur, and this process of water sinking is called convection (the term that some climate modellers prefer to avoid). Now, this very cooling processes causing water to sink is the main driver of classical overturning circulation …
Speaking of the cooling around Greenland – unless it coincided with massive surface freshening it is expected to accelerate deeper mixing and deep water formation fueling AMOC. In other words, when surface freshening reaches a certain point (call it threshold), the cooling may not be sufficiently strong to puncture through the layer of shallow stratified water (salinity is another factor controlling density). Something like this happened in the late 1960s and was associated with the so-called Great Salinity Anomaly. But was it true that deep convection expected in the colder winters of the 1990s and mid 2010s was stopped by an excessive amount of freshwater required for its shutdown? What do the observations say? Could the cooling of the Subpolar North Atlantic (SPNA) over the past 50 years be equated to weaker vertical mixing and production of deep water masses? I do not think so. The episode of strong surface cooling that took place in the Labrador Sea – the principal location for deep convection, water mass renewal, ventilation, overturning (just name it) – that lasted for nearly a decade, 1987-1995, had resulted in the deepest convection ever directly observed in the SPNA (we are talking about an 80-year instrumental record) reaching as deep as 2500 m and pumping loads of O2, CO2 and naturally freshwater into the deeper limb of AMOC (lots of publications discussed significance of this event for the rest of Atlantic Ocean). Well, this was not the first event of “systematically” strong deep convection in the last century – look in the 1950s, for example, the deep water was cold and fresh (fresh other than low-salinity means well ventilated for known reasons), and the thing of the 1990s was not the last one to note! More recently (and how this could be ignored?), starting in 2012, a new phase of deep convection, deep water cooling and densification, and hence ventilation and overturning came to the SPNA. We document this recent event of increased convection in oxygen, carbon dioxide, freons, SF6, freshwater and a bunch of other useful tracers of, once again, ocean’s overturning. And when saying “overturning” I do not mean what many climate experts have failed to see in their coupled climate models, but what is meant here is strong deep mixing and water mass production that is still on, and the most recent convection depth in the Labrador Sea is well over 2000 m!
Well, thinking that cooling is a result of shut down is easily opposed by my and not only my (we call it a classical oceanography going back to Emil Lentz, Fridtjof Nansen, Henry Stommel) knowledge and understanding that cooling at higher latitudes is a process driving water sinking up north and spreading all the way across the ocean, and through this simple process ocean’s overturning is maintained. Unless excessive surface freshening prohibits densification, but basing on REAL-WORLD observations this is not happening – the SPNA is happily eating up all the freshwater it receives from air, land, Arctic, Greenland, digesting it, mixing with other waters and forming a glorious cool dense water mass, we refer to as Labrador Sea Water.
As my final note, it is very disappointing to me and many colleagues and friends of mine putting tremendous amounts of effort in observing this interesting region of the ocean that some climate scientists keep systematically ignoring a wealth of publications supporting the points that do not fit the presented paradigm. What surprised me a couple years ago was that the convection of the late 1980s to mid-1990s was not even mentioned in the widely publicized paper that stated that AMOC was slowing in the end of the century, especially 1990s (which was attributed to lower temperatures, which was really opposite to what we observed, see my comments above). Now, 2012-2018, we witness another boost of moderate-to-strong convection. Of course, the SPNA cooling of 2014-2015 contributed mightily to making this happen – which again contradicts the point that surface cooling is a show-stopper … well, an observational oceanographer would argue that it is quite on contrary. There is a wealth of material published on these deep-mixing and dense water mass production events. All who are willing to know better are more than welcome to ask, there is a lot to be seen before jumping to any kind of conclusion.
Well, why do some people refuse to see what there is actually happening down deep? Can it be because of neglect or just unwillingness to accept the inconvenient truth?
PS. My points agree with the results showing that a slowdown of AMOC happened ~150 years ago (something of that order), and what we see now is more like cycles of deep mixing and densification speeding up in the 1950s, 1990s, now (!!) and slowing down. The deep ocean does know better when it has some cold high-oxygenized water entering its veins… and our mission is just to be there to see this happening.
[Response: Dear Igor, great to see you commenting here – this kind of discussion is just what we were hoping for! I appreciate the points you make, but I do not think there is such a disconnect between modelers and observational oceanographers as you suggest. I do talk to observational oceanographers (and in fact have been on several cruises myself, although a long time ago). The fact that cold surface waters promote convection is of course also well-known to modelers and occurs in the models as well – so we fully agree on that. The time intervals with strong convection that you mention nicely fit the particularly cold periods in the SPNA. However, the way I interpret this is as a negative feedback on the AMOC (in fact, one of my first papers as a young postdoc was on this very feedback). The AMOC will respond with some delay (8-10 years according to Jungclaus et al. 2014) to this convection, so the fact that the AMOC recovered after the cold phase in the 1990s fits this, and the more recent cold phase may well initiate another recovery soon. Weak AMOC -> SPNA cools -> stronger convection -> with some delay the AMOC recovers. That can explain the decadal oscillations we see.
That, however, does not answer the question of why the SPNA shows a long-term cooling trend despite global warming. We suggest that this is a sign of a weakening AMOC, which you may expect when increasingly adding freshwater to the system. That feedback I described will then operate in a gradually colder, fresher SPNA. One way to think of this is that you need colder temperatures to keep convection going in the presence of freshwater input, and that is what is happening.
So that is my interpretation – let me know if you think this contradicts observational data. Thanks again, Stefan]
74 CCHolley says:
“Seems to me when we look at sea surface temperatures only, they seem to have started to rise about 1950 and certainly by 1970.
Thanks for the link, CC. Interesting. For a closer look, let’s zero in on the principal culprit, the North Atlantic:
According to the caption, this is a representation of the AMOC cycle itself. I see a peak around 1945, followed by a nose-dive from just after 1950 through 1975, when the curve reverses itself and begins to rise. Looks to me like the opposite of Rahmstorf’s claim that the AMOC weakening really got going after mid-century, due to a rapid increase in CO2-induced warming, as no such warming is represented in any of the data, land or sea. It’s necessary, moreover, to keep in mind, as I’ve already stressed, that the low point (i.e., turning point) of a trend cannot possibly be responsible for any effects that might occur later on, as the trend rises.
Rahmstorf points, moreover, to a trend identified by the IPCC as beginning as early as 1901, an unusually cold period in recent history, when CO2 levels were much lower than they are today. If the AMOC slowdown began then, it’s very difficult to see how warming due to CO2 could have been the culprit.
Al Bundy says
[Response: You’d expect some decline, but not by as much as the AMOC declines because the Southern Ocean takes up a lot of CO2 as well. -Stefan]
AB: True, but that begs the question: is the Southern Ocean doing any better? Note that the lack of sinking by cold but fresher surface waters is what’s driving the melting of the ice shelves by warmer and saltier deep water.
“you are all hopelessly captured, victims of your own failure to think independently”
Actually I have been both a sceptic and warmist, for want of better terms, so I certainly am not rigid in my views. I think independently, and go where the most compelling science leads.
Science teaches people to be sceptics, and kick any new idea or new data to death to stress test it . You possibly see me doing this with various people on this website on some of the mitigation ideas.
The only reason most people on this website accept agw is it has been stress tested many times, and keeps winning the argument. Your background by your own admission is in the humanities (nothing wrong with those by the way).
I wonder if you have been on both sides of the climate debate. You think you think independently, but at times you just argue for the sake of scoring points, and believe me its transparently obvious.
You are an educated man, and probably very good in your field, and asked a good question about the apparent time discrepancy, but I suggest read the book “Skeptic by Michael Shermer” which is on real, healthy, rational scepticism.
Oh look, your graph of north atlantic ocean warming shows it increasing from almost exactly 1975 onwards as I stated. Thank’s so much. This is the point of significant decline in the amoc.
But please notice the linear trend over the entire time period of 1880 – 2018 is one of substantial warming. This is consistent with a mild weakening of the amoc from about 1901 – 1975. Remember other factors may have influenced the amoc rather than simple ocean warming during the early period. The warming is very bumpy, but then so was the rate of slowdown in the amoc to some extent. Natural variation easily explains the lack of a precise synchronisation of the variables.
“According to the caption, this is a representation of the AMOC cycle itself.”
It doesn’t say anything remotely like this. It just talks about the amoc in recent times and meetings about the issue. Good quality long term data on the amoc was not even available when the article in the link was written!
“Rahmstorf points, moreover, to a trend identified by the IPCC as beginning as early as 1901, an unusually cold period in recent history, when CO2 levels were much lower than they are today. If the AMOC slowdown began then, it’s very difficult to see how warming due to CO2 could have been the culprit.”
Actually the ocean warming data in your link do show very slight warming trend from 1900 until 1930, when it accelerates more steeply. Its the trend that counts, not whether its an “unusually cold period”.
The warming early last century was almost certainly driven by a combination of CO2, solar activity and volcanic activity. We have data that all three changed in a way conducive to warming, but the data is not accurate enough to be certain of the proportionality of each. What we do have are three plausible, data based explanations, so we dont need no “magical thinking” about mysterious causes. The frustration is more that we have the annoying complexity of three causes, but then nature creates this complexity all the time.
73 nigelj says: Victor @68
nj: “Honestly Al Bundy has you summed up perfectly. Your rhetoric is childish points scoring and game playing, and shows no desire to learn or admit you are wrong.”
No rhetoric. And I’ll admit I’m wrong when I’m proven wrong.
“V: According to the same graph, air temps fell close to an all time low in 1975. And once again, you can’t assess the effect of a temperature rise based on the time it began.”
nj: So what, the warming trend started from 1975 or near enough such that its pedantic nit picking to dispute it. It correlates well with the amoc slowdown. The more temperatures increased after 1975, the more it slowed down.
V: Rahmstorf dated the increase to 1950, not some time after 1975. And no, that’s not near enough.
nj: “OT and it has been explained to you literally a dozen times that the near flat period of temperatures mid last century was due to aerosols.”
That’s not even wrong. It’s beside the point. It’s the absence of mid-century warming that counts in this case, not some theory attempting to explain why the expected warming never happened.
MA Rodger says
Victor the Troll @80,
You are now beginning to stray way outside sensible discussion. The graphic you source from an article on a website title RAPID-WATCH: Monitoring the AMOC but except being on this website, there is no mention of AMOC, either (as you tell us there is) in the graphic’s caption or the rest of the article. The graphic shows not the AMOC but the Atlantic Multi-decadal Oscillation or AMO (un-detrended).
If you venture further to the research paper being discussed in the website article Sutton & Don (2012), you will find mention of the AMOC and discussion of its influence and the influence of other drivers on the AMO as understood (or not) prior to 2012, “prior to” because this was not the subject of the analysis. And note that such AMOC discussion is mostly pretty muted stuff, the exceptions referencing modelling work – Knight et al 2006 (which appears to be a referencing error) and Delworth & Mann (2000). If the AMO were considered a useful predictor of AMOC, do you thing we would be descussing this ‘cold blob’ in this manner?
And another comment you make that stretches credence to beyond breaking-point is that IPCC AR5 SPM Fig 1 in any way at all shows a cold blob “beginning as early as 1901.” It is possible to examine SST trends on the GISTEMP mapping page. This shows not the faintest sign of any ‘cold blob’ in trend from 1900 ending prior to 1950.
Mal Adapted says
Possibly ;^D! To be sure, successfully making a substantive point on RC is presumably self-enhancing for any of us! That wasn’t really my point, however. It was that the only substantive points left to make in the AGW ‘debate’ are political.
85 MA Rodger says: Victor the Troll @80, You are now beginning to stray way outside sensible discussion. The graphic you source from an article on a website title RAPID-WATCH: Monitoring the AMOC but except being on this website, there is no mention of AMOC, either (as you tell us there is) in the graphic’s caption or the rest of the article. The graphic shows not the AMOC but the Atlantic Multi-decadal Oscillation or AMO (un-detrended).
Victor the Troll: You say “AMO” I say “AMOC.” Let’s call the whole thing off!
Hapless MA: If you venture further to the research paper being discussed in the website article Sutton & Don (2012), you will find mention of the AMOC and discussion of its influence and the influence of other drivers on the AMO as understood (or not) prior to 2012, “prior to” because this was not the subject of the analysis. And note that such AMOC discussion is mostly pretty muted stuff, the exceptions referencing modelling work – Knight et al 2006 (which appears to be a referencing error) and Delworth & Mann (2000). If the AMO were considered a useful predictor of AMOC, do you thing we would be descussing this ‘cold blob’ in this manner?
V: First of all, the graph I displayed is clearly labeled “North Atlantic Temperature.” That speaks for itself, no? I was looking for a graph of N. Atlantic temperatures and that’s what I found. Secondly, I made no reference to the article itself, just that one graph. I’m responding to Rahmstorf’s paper, not this one.
Hapless MA: And another comment you make that stretches credence to beyond breaking-point is that IPCC AR5 SPM Fig 1 in any way at all shows a cold blob “beginning as early as 1901.” It is possible to examine SST trends on the GISTEMP mapping page. This shows not the faintest sign of any ‘cold blob’ in trend from 1900 ending prior to 1950.
V: Take that up with Rahmstorf, not me: “. . . the Atlantic overturning circulation (sometimes popularly dubbed the Gulf Stream System) has weakened significantly since the late 19th Century, . . .” (see above). Also, from the abstract of the original paper: “We find this fingerprint both in a high-resolution climate model in response to increasing atmospheric carbon dioxide concentrations, and in the temperature trends observed since the late nineteenth century. The pattern can be explained by a slowdown in the AMOC and reduced northward heat transport, as well as an associated northward shift of the Gulf Stream.”
As far as AMO is concerned, once more see above: “There is another well-known mode of Atlantic temperature variability known as AMO, which correlates strongly with our AMOC index.”
AMO, AMAS, AMOC. I love you too, Mr. R. :-)
Kevin McKinney says
Oh, that was neither a pose, nor indignant. That was me, feeling tired and jaded, and maybe even a little dizzy, from repeated trips around the Victorian merry-go-round. You’ve had multiple rational responses from me, and while I will readily admit that you’re an ingenious rationalizer and rhetorician, in the end you fall back on nonsense (as for instance the ‘lack of volcanic eruptions’ silliness of late unlamented memory.)
Already done, several times, but most recently and most specifically here:
Short version: detectibility isn’t the same thing as existence. (Otherwise, if I remember my dilettante readings in epistemology correctly, we’d all be Berkleyan Idealists.)
More explicit version: The fact that the warming effect of CO2 emissions in the 19th and early-to-middle 20th century was too small to detect given actual levels of unforced variability and the confounding effects of changes in other forcings does NOT mean that the increase in CO2e concentrations was unreal or immaterial.
MAR @85 you are right theres no mention of the amoc in the graphs caption, but there is a brief mention in the article of “International Science Meeting on the Atlantic Meridional Overturning Circulation (AMOC)”. None of this supports any of Victors conclusions.
79 Igor Yashayaev, good comment when people speak their truth and stand up for it publicly.
Kevin McKinney says ” while I will readily admit that you’re (Victor)an ingenious rationalizer and rhetorician, in the end you fall back on nonsense (as for instance the ‘lack of volcanic eruptions’ silliness of late unlamented memory.)”
Victors comments are mostly all pure rhetoric, pure sophistry. I can play that game very well, but I will not swim in that perverted, shallow, stinking ocean of word play. I suspect neither would you. It’s a question of standards.
Kevin McKinney says:
“The fact that the warming effect of CO2 emissions in the 19th and early-to-middle 20th century was too small to detect given actual levels of unforced variability and the confounding effects of changes in other forcings does NOT mean that the increase in CO2e concentrations was unreal or immaterial.”
V: No one says it was unreal — only insignificant. That’s not me, by the way, but a general consensus among many climate scientists:
“1915 to 1945 warm period could not be caused by atmospheric CO2. Global temperatures rose steadily in the 1920s, 1930s, and early 1940s. By the mid 1940s, global temperatures were about 0.5 °C (0.9° F) warmer than they had been at
the turn of the century (Figure 1). More high temperature records for the century were recorded in the 1930s than in any other decade of the 20th century (Fig. 2). Glaciers during this period retreated and, in general, followed the warming climate pattern. All of this occurred before CO2 emissions began to soar after 1945 (Fig. 3), so at least half of the warming of the past century cannot have been caused by manmade CO2.” http://myweb.wwu.edu/dbunny/pdfs/CO2_past-century.pdf
“The scientists who brushed aside Callendar’s claims were reasoning well enough. (Subsequent work has shown that the temperature rise up to 1940 was, as his critics thought, mainly caused by some kind of natural cyclical effect, not by the still relatively low CO2 emissions. . .” https://history.aip.org/climate/co2.htm
“Of the rise in global atmospheric temperature over the past century, nearly 30% occurred between 1910 and 1940 when anthropogenic forcings were relatively weak.” https://www.nature.com/articles/ngeo2321
“Using an optimal fingerprinting technique we robustly detect a significant natural contribution to the early 20th century warming. In addition, the amplitude of our simulated natural signal is consistent with the observations. Over the same period, however, we could not detect a greenhouse gas signal in the observed surface temperature in the presence of the external natural forcings. Hence our analysis suggests that external natural factors caused more warming in the early 20th century than anthropogenic factors.” https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2005GL023540
“The huge warming of the Arctic that started in the early 1920s and lasted for almost two decades is one of the most spectacular climate events of the twentieth century. During the peak period 1930–40, the annually averaged temperature anomaly for the area 60°–90°N amounted to some 1.7°C. Whether this event is an example of an internal climate mode or is externally forced, such as by enhanced solar effects, is presently under debate. This study suggests that natural variability is a likely cause, with reduced sea ice cover being crucial for the warming. https://journals.ametsoc.org/doi/abs/10.1175/1520-0442(2004)017%3C4045:TETWIT%3E2.0.CO%3B2
MA Rodger says
Victor the Troll @87,
You are such a twit.
(1) The reason I delved into Sutton & Dong (2012) was because that is the way a scientific discussion should be conducted. But that nicety is obviously way over your head.
(2) You now insist that the AMO can act as a substitute for the AMOC. Yet the one chracteristic of AMOC strength that is not reflected in the AMO is the characteristic under discussion here. So your attempt to conflate the two cannot stand.
Read what the OP says! You even manage to quote part of the relevant passage from the OP but, like some grinning idiot, feel that a single sentence is enough to some how support your brainless theorising.
And if you could be bothered to look in the ‘Extended Data section’ of Caesar et al (2018) – specifically Extended Data Figure 8b on page 16 – you will seen that to produce that correlation both AMO and AMOC are detrended. It is the wobbles that show correlation. The trends through the 20th century do not correlate. Indeed it would be mighty strange if they did. Without detrending, AMO is rising and AMOC is weakening.
Is it then funny that you fail to grasp this situation? Is it acceptable that you present an un-detrended AMO graphic as though it was AMOC?
(3) And sticking with that Extended Data Figure 8 but examining the upper graph, it is evident that the smoothed AMOC trace has been weakening since the late 19th century. But its significant decline only begins from the late 1950s and that smoothed decline is supported by unprecedented weakening from the 1970s, that is evidently unprecedented in the data since 1880 but it is more than that. Caesar et al (2018), quoting Rahmstorf et al (2015), state “the AMOC weakness after 1975 is an unprecedented event in the past millennium.” Caesar et al go on to say:-
Victor, you are scrabbling about to find material to support your ridiculous theorising that CO2 levels do not correlate enough with SAT, SLR or whatever so as to disprove AGW. Yet you are flat wrong with your theorising and you are flat wrong here, ridiculously so.
Barton Paul Levenson says
V 87: You say “AMO” I say “AMOC.”
BPL: The first is the Atlantic Multi-decadal Oscillation. The second is the Atlantic Mid-Ocean Current. They are not even remotely the same thing.
Hank Roberts says
Oscillation, circulation, let’s call the whole thing off.
93 MA Rodger says:
4 Jun 2018 at 9:10 AM
“Victor the Troll @87, You are such a twit.”
V: And you, Hapless MA, are such a hopeless pedant.
MA: You now insist that the AMO can act as a substitute for the AMOC.
V: I “insisted” on no such thing. The graph I linked to is a graph of North Atlantic ocean temperatures. Period. That’s all it meant as far as I’m concerned. The data presented on that graph is inconsistent with Rahmstorf’s claims. THAT’s my point, which has nothing to do with the relation, if any, between AMO and AMOC.
MA: Without detrending, AMO is rising and AMOC is weakening.
V: I could care less about the relation between AMO and AMOC. That was Rahmstorf’s claim, not mine. It’s a temperature graph, get it? If it also represents AMO, that’s beside the point as far as I’m concerned. Your proclivity for nit picking would be amusing if it weren’t such a huge distraction.
MA: Caesar et al (2018), quoting Rahmstorf et al (2015), state “the AMOC weakness after 1975 is an unprecedented event in the past millennium.” Caesar et al go on to say:-
“Although long-term natural variations cannot be ruled out entirely (refs), the AMOC decline since the 1950s is very likely to be largely anthropogenic, given that it is a feature predicted by climate models in response to rising CO2 levels. This declining trend is superimposed by shorter-term (interdecadal) natural variability.”
V: Well there you have it. “. . . a feature predicted by climate models in response to rising CO2 levels.” If you are focused ONLY on CO2 levels then yes, it’s possible to make all sorts of dubious assumptions. Looks to me like this is what Rahmstorf did as well. Rising CO2 levels are relevant ONLY if they can be associated with rising temperature levels. But as I’ve pointed out time after time on this blog and elsewhere, there is NO evidence of such an association. Which is why I pointed us to the graph that has you so tied up in knots.
MA: Victor, you are scrabbling about to find material to support your ridiculous theorising that CO2 levels do not correlate enough with SAT, SLR or whatever so as to disprove AGW. Yet you are flat wrong with your theorising and you are flat wrong here, ridiculously so.
V: CO2 levels are meaningful ONLY if they correlate with temperature levels, which they very clearly do NOT. Even someone as dense as yourself should be able to see that.
Hank Roberts says
Apology for the persistent digression. Someone is wrong on the Internet….
Victor @92 claims “V: No one says it was unreal — only insignificant ( the effects of CO2 emissions early last century). That’s not me, by the way, but a general consensus among many climate scientists:”
A general consensus among many climate scientists is not a consensus of all climate scientists. And what of Victors partial consensus? He quotes an old article from a website http://www.edu.bunny which gives no name for the author of the article, and is clearly a very slanted stupid sort of article, and this article may or may not even be written by a climate scientist. We can ignore this article.
We then have a link to one single research paper, out of dozens of research papers on the subject. And we have a book from Spencer Weart, which is really just his opinion as one person. So we don’t even have much of a partial consensus.
Hank Roberts says
Victor: “It’s the absence of mid-century warming that counts in this case, not some theory [sulfate aerosols] attempting to explain why the expected warming never happened”
10 points for arguing that a current well-established theory is “only a theory”, as if this were somehow a point against it.
10 points for arguing that while a current well-established theory predicts phenomena correctly, it doesn’t explain “why” they occur, or fails to provide a “mechanism”.
Kevin McKinney says
Ah, but you invariably go on from asserting its “insignificance” to the assumptions that it therefore doesn’t matter and that it can safely be disregarded, which are pretty much the same the same things, IMHO, as saying that it is ‘unreal’ or ‘immaterial.’
You do cite some authorities. First up is Don Easterbrook, who, however, is not a climate scientist. He does hold a PhD in geology, and has done serious (albeit now ‘long-ago’) work in glaciology, but he is deep in denial about most of the rest of the relevant science, is factually unreliable, and generally behaves like a crank by, for example, accusing NASA and NOAA of fraud. Here’s a summary of such:
There’s a small example of that in the bit that you quote. Easterbrook says, in the context of a discussion about global temperatures, that “More high temperature records for the century were recorded in the 1930s than in any other decade of the 20th century (Fig. 2).” That’s only true for US high temperatures, but he doesn’t say in the text that he has shifted ground, leaving the unwary reader to assume that this ‘most records’ claim is true of global temps as well–wary readers will have read the graph labelling as well as scanned the contours. Easterbrook here is sloppy at best, willfully deceptive, more likely.
Your second quote is from Spencer Weart, whom you quote as saying that “the temperature rise up to 1940 was, as his critics thought, mainly caused by some kind of natural cyclical effect, not by the still relatively low CO2 emissions. . .”
Let me do a little highlighting there: “mainly caused.”
“Mainly” does not equal “exclusively,” nor does it imply that the ‘secondary’ cause, anthropogenic warming, was ‘insignificant’–only that it was lesser (about which we do not disagree).
Third quote: “…between 1910 and 1940 when anthropogenic forcings were relatively weak.”
“Relatively” weak does not equal “exclusively,” nor does it imply that the ‘secondary’ cause, anthropogenic warming, was ‘insignificant’. In fact, let’s go on and quote the next couple of sentences from that abstract: “This early warming has been attributed to internal factors, such as natural climate variability in the Atlantic region, and external factors, such as solar variability and greenhouse gas emissions. However, the warming is too large to be explained by external factors alone…”
The only inference one can draw from that is that the ‘external factors’ did indeed “contribute” a portion of the observed warming, albeit they are insufficient to explain it all. (Figure 1 on the same page, by the way, is a graph showing GMST plus CO2, solar and volcanic forcings. It’s interesting to note the relationships among all the forcings and GMST.
Your third quote simply says (yet again) that there was more natural than anthropogenic warming. Again, that has never been at issue. I said the same thing in my comment. (Did you ever bother to read it?) To quote it again:
“[anthropogenic warming] would correspond to a couple of tenths of a degree C. That would be swamped in the record by natural variability, but nonetheless it would exist as a warm bias relative to a hypothetical ‘no additional GHG’ case.
Last quote? Same story. It says that the issue “is presently under debate. This study suggests that natural variability is a likely cause…”
Not exactly conclusive, is it?
Summing it up, I see nothing in your quotes to suggest that the estimate that the early century warming owing a couple of tenths of a degree C to anthropogenic forcings is wrong. Indeed, I think a couple of those source lend some qualitative support to that estimate.