the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Dec 2023
Tipping points in ocean and atmosphere circulations
Abstract. In this review, we assess scientific evidence for tipping points in ocean and atmosphere circulations. The warming of oceans, modified wind patterns and increasing freshwater influx from melting ice hold the potential to disrupt established circulation patterns. The literature provides evidence for oceanic tipping points in the Atlantic Meridional Overturning Circulation (AMOC), the North Atlantic Subpolar Gyre (SPG), and the Antarctic Overturning Circulation, which may collapse under warmer and ‘fresher’ (i.e. less salty) conditions. A slowdown or collapse of these oceanic circulations would have far-reaching consequences for the rest of the climate system and could lead to strong impacts on human societies and the biosphere.
Among the atmospheric circulation systems considered, we classify the West African monsoon as a tipping system. Its abrupt changes in the past have led to vastly different vegetation states of the Sahara (e.g. “green Sahara” states). Evidence about tipping of the monsoon systems over South America and Asia is limited however, there are multiple potential sources of destabilisation, including large-scale deforestation, air pollution, and shifts in other circulation patterns (in particular the AMOC). Although theoretically possible, there is currently little indication for tipping points in tropical clouds or mid-latitude atmospheric circulations. Similarly, tipping towards a more extreme or persistent state of the El Niño-Southern Oscillation (ENSO) is currently not fully supported by models and observations.
While the tipping thresholds for many of these systems are uncertain, tipping could have severe socio-environmental consequences. Stabilising Earth’s climate (along with minimising other environmental pressures, like aerosol pollution and ecosystem degradation) is critical for reducing the likelihood of reaching tipping points in the ocean-atmosphere system.
- Preprint
(3011 KB) - Metadata XML
-
Supplement
(2381 KB) - BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on egusphere-2023-2589', Anonymous Referee #1, 29 Dec 2023
The review “Tipping points in ocean and atmosphere circulations” discusses the current state of research regarding potential “tipping points” in the Earth system that may be inherent in circulation systems. The topic is certainly important and suitable for the journal.
The aim and content of the study is clear, but could be better justified; and could also become a bit more ambitious. My main concern in this context is that there has been a large number of reviews about Earth system “tipping points” in recent years, e.g. Lenton et al., 2008 (PNAS), Lenton 2013 (Annual Review of Environment and Resources), Schellnhuber et al., 2016 (Nat Clim Change), Bathiany et al., 2016 (Dyn Stat Clim Sys), Steffen et al., 2018 (PNAS); Boers et al., 2022 (ERL), Wang et al., 2023 (Rev Geophys), Armstrong Mc Kay et al., 2022 (Science), and a several 100 pages long Global Tipping Points Report (2023).
It sometimes almost seems like scientists would spend more time on such reviews than they spend on actually creating new knowledge and reducing the uncertainties. To offer new insights, a new review paper should find its own angle and focus on content that goes beyond previous reviews. I think that the focus on circulation-related tipping elements is a promising idea, in particular regarding the atmospheric circulation. I believe that there is a bit more to discuss than mainly repeating contents from previous studies. Potentially interesting questions the authors could discuss in more detail are:
• Are circulation systems more or less prone to “tipping” than terrestrial systems or ice sheets, and why?
• There are many insights from hydrodanymical theory about nonlinear regime shifts, from the very conceptual Lorenz system and fundamental phenomena like the onset of turbulence in fluids, to hydrodynamic instabilities of flows (barotropic and baroclinic instabilities), and the phenomena of abrupt monsoon onsets (as part of the annual cycle) on aquaplanets and the present-day Earth. Can these insights inform us on potential tipping points in atmospheric circulation under greenhouse (and/or other anthropogenic) forcing?
• Why do the authors cover the major monsoon systems but not the East Asian summer monsoon? There is evidence about abrupt shifts in this monsoon system in paleo records, e.g. Wang et al., 2008.
• Can we transfer knowledge from one monsoon system to another, or are they too different?
• What is the (nonlinear) response of the atmospheric circulation to topography? What happens when ice sheets shrink? Do we have evidence for that from reconstructions (e.g. dust record in Greenland ice core)?
• How does model resolution and complexity affect the stability of circulation systems? Are there any hypotheses about that, may be not in general, but regarding ocean eddies?
• Clouds seem to show nonlinear behaviour in several ways; how precisely would this translate to climate timescales and tipping behaviour? Isn’t the high spatio-temporal variability of cloud formation and dissolvement already an argument against tipping points, at least against multiple alternative states?
• What needs to happen precisely to answer these questions (beyond general statements like improving models and data).In my view, a second major caveat of the current draft is that the labels of “tipping” potential and the uncertainty, as summarised in Fig. 1 and Table 1, involve too much subjectivity. The authors write that the assessment “… was conducted by an expert group and does not necessarily represent the view of the entire community.” I believe that one can do better than that in a review that is meant to represent the general state of knowledge, and not only the author’s perspective alone - either by accepting that uncertainties are not quantifyable and hence not providing any label for the plausibility of tipping, or by formulating specific criteria that would be transformed into these labels transparently.
Some of the confidence levels are not convincing to me given the large uncertainties of all tipping elements, in particular the “++” labels for the ocean circulation cases. For example, as a layperson, I would interprete the label “Tipping System (confidence level): yes (medium)” as the statement that it is scientifically relatively clear that these systems have tipping points. But this is not at all the case. Another example is that the authors write “we classify the West African monsoon as a tipping system”, but it is unclear to me why particularly this monsoon, and less so other monsoon systems (let alone the East Asian monsoon, which is largely ignored although it also shows nonlinear shifts in paleo records)?
Third example: If there are models that show “tipping” of blocking behaviour (Sect 4.3.1), why is the authors assessment “no tipping” with low confidence (Sect 4.3.2), while the AMOC is labeled as “tipping” with medium confidence?
Specific minor commentsAbstract
- “Evidence about tipping of the monsoon systems over South America and Asia is limited – however, there are multiple potential sources of destabilisation, including large-scale deforestation, air pollution, and shifts in other circulation patterns (in particular the AMOC).”
change of topic in mid-sentence, from monsoons to AMOC.Introduction
• unclear: The focus is on tipping points in the future, due to human activity? This is implied by the text but not clearly stated anywhere in the abstract or introduction.
• The introduction is extremely short. I was expecting some more background and a justification why the authors focus on circulation systems (e.g. as opposed to tipping of ice sheets or ecosystems), and the rationale and structure of the article. One could also explain the methods (how was literature collected / considered, how were assessment criteria defined).Fig. 1
- tipping under human forcing?
- what is considered “tipping” in this article? “shift to a different state” is vague, and cited papers disagree in their definition. This paper should stick to a certain definition.l 149-150: “nor the presence of external forcings such as increasing greenhouse gases” – The authors do take greenhouse gases into account (otherwise the AMOC would not destabilise), though indeed in a rather simplistic way (stable forcing and then linear increase with extrapolation into the future).
l 145-155: “However, the claim that we might expect tipping within a few decades is – in the view of the present authors – not substantiated enough.” I agree with the authors. However, rather than elaborating mostly on the “pro tipping” literature and then saying that one does not agree, it would be more convincing to let the literature speak for itself, and also elaborate a bit on the evidence against the tipping hypothesis. This would be more suitable for a review paper than just making a subjective statement.
l 164: Sentence is unclear. What does “these” refer to?
l 170:
“even the current generation of climate models have quite low spatial resolution and do not characterise narrow currents, eddies and processes such as horizontal and vertical mixing very well (Swingedouw et al. 2022).” It would be nice to read if, how and why resolving eddies might make models more prone to tipping.Fig. 4:
Is there a reference for the experiment and the results? Is this an overshoot in CO2 because emissions stop, or an overshoot because of negative emissions? Does the AMOC have a delayed recovery or alternative states in this model?l 209-210: “Although the AMOC does not collapse in this model, it seems unlikely that it will recover its former strength on human timescales.” Why does this seem unlikely? What’s the evidence? And what are “human timescales”?
l 215-216: “while if it is preceded by…” what do you mean, a feedback being preceded by another?
l 240: “we may be close to an AMOC tipping point (Michel et al., 2022), as do the studies of Boers (2021) and Ditlevsen and Ditlevsen (2023) cited above”. Not really; for example Boers (2021) only argues that the AMOC shows slowing down, but it does not make statements about whether a tipping point exists and how close it is. And Ditlevsen and Ditlevsen (2023) assume that a tipping point exists, and only determine its proximity based on this assumption.
l 248-251: “More paleo-reconstructions of AMOC strength, ocean surface temperature, and other AMOC-related properties with high temporal resolution, using appropriate proxies and careful chronological control performed for key past periods (e.g. last millennium, millennial-scale climate change events, previous interglacials), hold great potential to improve our understanding about the AMOC as a tipping point.”
I (and possibly readers) would be curious to learn more – why is there a great potential, what needs to happen, what are the proxies?l 252: “develop improved metrics” means AMOC fingerprints? This term is used in Sect 2.1.1, but then dropped.
Fig. 6a: Caption says 2020-30, but figure says 2020-39. Both is in the future, but “projection” is not in the title, in contrast to the other three subfigures. Why?
b) “changes ...by…” compared to what reference period?l 526: potential tipping behaviour in the AMOC (relation to global monsoon described in West African monsoon below) or increase in the interhemispheric asymmetry of aerosol loading in the atmosphere beyond potential threshold levels could lead to large disruptions to monsoon systems.
l 569-570: “a process sometimes referred to as “induced tipping”.” Any reference?
l 607: “in one model” – but not an Earth system model. Also, the concern about deforestation and moisture recycling in general, which coupled the SAM and the rainforest, somehow comes out of the blue sky here, and would deserve 1-2 extra paragraphs.
l 612: “see 1.3.2.1 for more on Amazon dieback” This section does not exist.
l 625 “low emissivity for longwave radiation (heat),” - do you mean transmissivity, or really emissivity? Low compared to what? Probably to thicker clouds. But compared to no clouds, the emissivity is high.
And why do you compare high thin clouds with low thick clouds? Because these combinations are most common? With “high” vs “low” you mean their altitude, not their thickness? What about high thick clouds, like cumulonimbus?l 637: “the transition of shallow cloud layers from closed to open-cell geometries” How would the dynamics in droplet growth describe in the previous sentences lead to that? 1-2 sentences to explain the connection would be helpful.
l 693-695: can now be updated with newest observations
l 772-773: “Models with a strong AMOC reduction in the future tend to project a much stronger poleward shift of the jet than models with a weaker AMOC reduction” Why does this happen?
l 777: “Arctic is warming more rapidly than the rest of the planet, partly driven by sea ice loss” – sea ice loss (albedo feedback) is indeed not the only reason; maybe cite more comprehensive studies like Pithan & Mauritsen 2014
l 784-794: The explanation is not quote clear to me, how the jet stream could undergo tipping. The resonance behaviour seems to be the positive feedback that pushes the jet stream to another regime? Again, this is a paragraph where the paper would benefit from more explanations and interpretation, beyond describing results from the cited papers.
l 801-804: Unclear what the connection between these sentences is. If the models are so uncertain, what evidence is it that some show tipping behaviour in blocking? And why “in addition”? These sentences make opposite statements in some way.
l 903: Why is the process complexity a “conceptual issue”? Conceptually, feedbacks are well defined, I’d rather say that the complexity is a practical limitation?
l 916 and elsewhere: biased (with one s, not two)
l 932: The paragraph on TIPMIP reads like an afterthought that is only there to mention the project. It could be either removed, or better integrated in the rest of the paper.
Table 1: Why arrows up and down instead of + and - signs for positive and negative feedbacks?
Citation: https://doi.org/10.5194/egusphere-2023-2589-RC1 -
CC1: 'Comment on AMOC statements in egusphere-2023-2589', Stefan Rahmstorf, 29 Mar 2024
This is generally an informative review worth publishing, but I’d like to flag a couple of issues which should be improved, or else may lead to misunderstandings.
- “AMOC bistability is model-dependent though, controlled by the balance of the positive and negative feedbacks that determine the salinity of the subpolar North Atlantic. It is not yet understood why the bistability occurs in some models and not others (Jackson et al., 2023).”
This statement seems to mix up models having a bistable AMOC regime, and models being in this bistable regime for present climate. As explained earlier in the article, it requires a special hysteresis experiment to test whether a bistable regime exists, and as far as I am aware every single model which has been tested in this way does have a bistable regime (the latest example being van Westen et al. 2024). So, as far as we know this bistability is not model-dependent but a very robust feature across a wide range of models from Stommel’s simple box model to modern climate GCMs.
What Jackson et al. 2023 have shown is merely that some models are not in this regime for present climate, a finding consistent with many other previous studies. That is not a fundamental model difference but a matter of tuning and accurate representation of salinity. However, the wording quoted above wrongly suggests that some models don’t have a bistable regime. This must be clarified.
- “It is therefore difficult to confidently discern potential recent trends from natural variability, due to disagreement between published studies (Bonnet et al. 2021, Latif et al., 2022, versus Qasmi, 2022).”
I do not see disagreement between these studies regarding recent trends; rather this again mixes up different issues.
Qasmi 2022 indeed analyzes recent trends in observational data (with the help of model simulations), namely the Atlantic ‘warming hole’ - and comes to the clear conclusion that it is anthropogenic. The same conclusion was reached earlier by Chemke et al. 2020 (which should be cited): “Analyzing state-of-the-art climate models and observations, we show that the recent North Atlantic warming hole is of anthropogenic origin”.
Latif et al. merely analyse CMIP6 models. As the IPCC has shown (figure SPM.5a of AR6 WG1 report), these models overall do not reproduce the ‘warming hole’ until the present and don’t show an AMOC weakening until now, only in future. An important finding of Latif et al. is, however, their Fig. 4 showing how the actual AMOC in CMIP6 models is correlated with the AMOC SST fingerprint of Caesar et al. 2018 (both cold and warm part), which supports the conclusion that the anthropogenic ‘warming hole’ discussed by Qasmi and Chemke indeed points to an AMOC weakening.
(Bonnet et al. 2021 is also not in disagreement with either of the cited other two studies but looking at a different aspect again.)
So there is no disagreement between these studies, but rather a model-observations disagreement which is very important for the tipping point risk discussion: the data suggest an anthropogenic AMOC weakening already in recent decades, which the CMIP6 models do not reproduce. Which suggests that the models understate the slowdown (and thus tipping risk). That echoes my first point, where many models are not in the bistable regime but observational data suggest the real AMOC is in the bistable regime, so the models are likely too far way from the tipping point.
To sum up, readers must not be confused with messages like “some models show bistability, some don’t” and “some studies suggest recent anthropogenic AMOC weakening, some don’t” which are not backed up by a careful reading of the cited evidence.
Citation: https://doi.org/10.5194/egusphere-2023-2589-CC1 -
CC2: 'Postscript on CC1', Stefan Rahmstorf, 30 Mar 2024
One more point:
- "However, the proxy data used in these studies have large uncertainties, and some other reconstructions show little evidence of decline (Moffa-Sanchez
et al., 2019, Killbourne et al., 2022)."
When you cite the comment by Kilbourne et al., please also note our reply to their comment, particularly our Fig. 2 which shows there is a high consistency amongst the reconstructions: https://www.nature.com/articles/s41561-022-00897-3
Citation: https://doi.org/10.5194/egusphere-2023-2589-CC2 - "However, the proxy data used in these studies have large uncertainties, and some other reconstructions show little evidence of decline (Moffa-Sanchez
-
RC2: 'Comment on egusphere-2023-2589', Anonymous Referee #2, 10 Apr 2024
The paper provides a well-written and comprehensive review of tipping points in global climate subsystems including ocean circulation and the monsoon systems. For each of the discussed subsystems the authors provide a paragraph on the evidence and a paragraph where the evidence is assessed with respect to potential tipping behavior. I find the assessment generally well-balanced. A complication in the discussion on tipping points is that there are very few observations of tipping from the instrumental record and hence paleoclimatic evidence must be used. As outlined below, I feel that the authors should specify why they see proxy records related to ocean circulation as evidence for tipping dynamics in the AMOC. For me this is far from obvious. The paper would also benefit from a better description of the feedbacks involved in modulating the West African Monsoon, particularly the role of the tropospheric circulation.
1) Definition of tipping. What is the definition of “tipping” employed here? Some of the classical definitions of abrupt climate change (response faster than the forcing, rate of change only determined by the climate system, not by the forcing, difficulty of eco-/ economic systems to adapt, etc. see for example National Research Council, 2002) are difficult to apply to proxy records. Please be more specific what qualifies the AMOC as a tipping element based on paleoceanographic data.
2) AMOC as a tipping element. There is no question that there is evidence for significant AMOC variations with huge consequences for climate and ecosystems. However, if the AMOC is actually a tipping element is much harder to determine and I would argue that there is not much unequivocal evidence for tipping dynamics in the AMOC. For example, Pa/Th, ∂13C and flow-speed related proxies do not show any indication for an abrupt decline in AMOC into HS1 (e.g., Stanford et al. 2011). Apparently, the slowdown is quite gradual and takes several millennia, inconsistent with the time scale of tipping of 15-300 years mentioned in line 212. By contrast, the onset of the AMOC (e.g., with the Boelling/Allerod interstadial or DO1) seems often indeed very abrupt and much faster than the slowdown. One could argue that the AMOC resumes almost instantaneously with the end of the anomalous meltwater flux (see for example ∂18O in Fig 4f in Stanford et al. 2011) at the end of the Heinrich Stadials, which might hint against a strong bi-stability of the AMOC and for a more linear relation between AMOC strength and freshwater flux as suggested by Liu et al. (2009). So again, in the light of conflicting results from climate models, how can we derive from proxy records that the AMOC is actually a tipping element? I am not ruling out that the AMOC is a tipping element, but is there enough evidence apart from some (mostly intermediate complexity) models to qualify the AMOC as one with ‘medium confidence’? Since this is an important question, we should be careful with the answer. Even a small and more gradual AMOC change might be very dangerous in certain regions of the world (see comment 4).
3) Collapse of AMOC (Line 126 “It also occasionally collapsed to an off-mode”): The recent literature does not support the existence of a “off-mode”. The recent assessment by Pöppelmeyer et al. (2023) finds a reduction of the AMOC of about 30% relative to the LGM during HS1. There is also proxy evidence for NADW formation during HS1. For example, based on εNd, Howe et al. (2018) find no evidence for strong changes in water mass provenance in the mid-depth South Atlantic between the LGM and HS1 and benthic isotopes support active deep-water formation in the North Atlantic during HS1 (Repschläger et al. 2021).
4) AMOC and WAM during the instrumental period. Personally, I have no confidence that the AMOC is actually a tipping element because both the palaeoceanographic data and the models are ambiguous. The focus on “tipping” might distract from the fact that even comparably moderate fluctuations in the AMOC can have significant and dangerous effects on ecosystems, economy and society. In this context, the paper would benefit from expanding to the very few examples of abrupt climate change in the instrumental record. The event that that is often cited as the most recent example of abrupt climate change is the abrupt onset of the multi-decadal catastrophic Sahel drought in the early 1970ies (briefly mentioned in line 546) with an abrupt reduction of precipitation on the order of 30% over nearly two decades and probably millions of victims. Lake Chad shrank by >90% over the following decades. Initially it was thought that overgrazing and desertification was to blame for the drought (Charney, 1975), but subsequent work made it clear that the drought is connected to a specific SST pattern with a negative SST anomaly in the North Atlantic and positive SST anomaly in the South Atlantic (Folland, et al. 1986, Bisautti, 2019, Pereira et al. 2022), an SST pattern we know as bi-polar seesaw from ice cores, sediment cores and climate models as a response to weakening of the overturning. It seems therefore likely that the 70ies Sahel drought is connected to a fluctuation of the thermohaline circulation as various authors suggest (e.g., Knight et al. 2005, Zhang and Delworth, 2006) and that the Charney-Effect is only second-order feedback. If the WAM is indeed a tipping element, why did the precipitation and the vegetation of the Sahel immediately recover (e.g., Heumann et al. 2007) after the drought with the onset of the positive phase of the AMO, although precipitation and vegetation was significantly reduced over decades? The Sahel likely turned into a complete desert during HS1 (there is evidence from fossil “Ogolian” dune fields, Collins et al. 2013), but it recovered synchronously with the onset of the Boelling interstadial, again not much evidence for bifurcation or an irreversibility in the African Monsoon, both on the millennial scale and the decadal scale.
I agree with the authors that AMOC reconstructions are highly uncertain. But it is evident from both data and models that the ITCZ/tropical rainbelt is very sensitive to changes in AMOC intensity on all time scales (Marshall et al. 2014, McGee et al. 2014). If the AMOC is already slowing down, this raises the question why Sahel precipitation and vegetation has increased in recent decades. In my view this shows that the AMOC was indeed dominated by multi-decadal variability as suggested by Latif et al. (2022). Based on the work of Wett et al. (2023) it is probably robust to say that there are no trends in the instrumental record of AMOC observations since 1993.
5) Monsoon, ITCZ and AMOC. The response of the Monsoon to AMOC slowdown is portrayed as a simple southward migration of the ITCZ. This is certainly a good model when it comes to areas primarily influenced by the clearly defined oceanic ITCZ, for example NE Brazil. However, it seems to me that this model is an oversimplification when it comes the monsoonal areas in Africa. Some meteorologists even argue that the ITCZ and the rainbelt located between the African Easterly Jet and the Tropical Easterly Jet (where 50 - 80% of the rainfall is produced by a relatively small number of mesoscale convective systems) are different systems and should not be confused (Nicholson, 2009, Fig. 18). If the response would be a simple southward migration of the rainbelt/ITCZ over Africa, we should see regions to the south of the ITCZ, where precipitation increases. For Africa and the Monsoonal areas this seems not to be the case (e.g., Stager et al. 2011). More recent work points to the location and intensity of the tropospheric jet streams as important processes modulating the strength and position of the African rainbelt (e.g., Farnsworth et al., 2011, Nicholson and Dezfuli, 2013). This should be mentioned in the paper.
6) Missing info on AMOC variability during interglacials. Much of the cited evidence for AMOC variability comes from the glacial period. In this context it might also be important to mention the 8.2 kyr Event as an example for an AMOC slowdown under interglacial boundary conditions. In Africa, this event was associated with aridification as documented by low lake levels (Gasse, 2000) and periods human abandonment in the southern Sahara (Sereno et al. 2008).
References
National Research Council: Abrupt Climate Change: Inevitable Surprises, National Academies Press, Washington, D.C., 2002.
Biasutti, M.: Rainfall trends in the African Sahel: Characteristics, processes, and causes, Wiley interdisciplinary reviews. Climate change, 10, e591, https://doi.org/10.1002/wcc.591, 2019.Charney, J. G.: Dynamics of deserts and drought in the Sahel, Quart J Royal Meteoro Soc, 101, 193–202, https://doi.org/10.1002/qj.49710142802, 1975.
Collins, J. A., Govin, A., Mulitza, S., Heslop, D., Zabel, M., Hartmann, J., Röhl, U., and Wefer, G.: Abrupt shifts of the Sahara–Sahel boundary during Heinrich stadials, Clim. Past, 9, 1181–1191, https://doi.org/10.5194/cp-9-1181-2013, 2013.
Farnsworth, A., White, E., Williams, C. J., Black, E., and Kniveton, D. R.: Understanding the Large Scale Driving Mechanisms of Rainfall Variability over Central Africa, in: African Climate and Climate Change, edited by: Williams, C. J. R. and Kniveton, D. R., Springer Netherlands, Dordrecht, 101–122, https://doi.org/10.1007/978-90-481-3842-5_5, 2011.
Folland, C. K., Palmer, T. N., and Parker, D. E.: Sahel rainfall and worldwide sea temperatures, 1901–85, Nature, 320, 602–607, https://doi.org/10.1038/320602a0, 1986.
Gasse, F.: Hydrological changes in the African tropics since the Last Glacial Maximum, Quaternary Science Reviews, 19, 189–211, https://doi.org/10.1016/S0277-3791(99)00061-X, 2000.
Heumann, B. W., Seaquist, J. W., Eklundh, L., and Jönsson, P.: AVHRR derived phenological change in the Sahel and Soudan, Africa, 1982–2005, Remote Sensing of Environment, 108, 385–392, https://doi.org/10.1016/j.rse.2006.11.025, 2007.
Howe, J. N., Huang, K.-F., Oppo, D. W., Chiessi, C. M., Mulitza, S., Blusztajn, J., and Piotrowski, A. M.: Similar mid-depth Atlantic water mass provenance during the Last Glacial Maximum and Heinrich Stadial 1, Earth and Planetary Science Letters, 490, 51–61, https://doi.org/10.1016/j.epsl.2018.03.006, 2018.
Knight, J. R., Allan, R. J., Folland, C. K., Vellinga, M., and Mann, M. E.: A signature of persistent natural thermohaline circulation cycles in observed climate, Geophysical Research Letters, 32, https://doi.org/10.1029/2005GL024233, 2005.
Latif, M., Sun, J., Visbeck, M., and Hadi Bordbar, M.: Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900, Nat. Clim. Chang., 12, 455–460, https://doi.org/10.1038/s41558-022-01342-4, 2022.
Liu, Z., Otto-Bliesner, B. L., He, F., Brady, E. C., Tomas, R., Clark, P. U., Carlson, A. E., Lynch-Stieglitz, J., Curry, W., Brook, E., Erickson, D., Jacob, R., Kutzbach, J., and Cheng, J.: Transient simulation of last deglaciation with a new mechanism for Bolling-Allerod warming, Science (New York, N.Y.), 325, 310–314, https://doi.org/10.1126/science.1171041, 2009.
Marshall, J., Donohoe, A., Ferreira, D., and McGee, D.: The ocean’s role in setting the mean position of the Inter-Tropical Convergence Zone, Clim Dyn, 42, 1967–1979, https://doi.org/10.1007/s00382-013-1767-z, 2014.
McGee, D., Donohoe, A., Marshall, J., and Ferreira, D.: Changes in ITCZ location and cross-equatorial heat transport at the Last Glacial Maximum, Heinrich Stadial 1, and the mid-Holocene, Earth and Planetary Science Letters, 390, 69–79, https://doi.org/10.1016/j.epsl.2013.12.043, 2014.
Nicholson, S. E.: A revised picture of the structure of the “monsoon” and land ITCZ over West Africa, Clim Dyn, 32, 1155–1171, https://doi.org/10.1007/s00382-008-0514-3, 2009.
Nicholson, S. E. and Dezfuli, A. K.: The Relationship of Rainfall Variability in Western Equatorial Africa to the Tropical Oceans and Atmospheric Circulation. Part I: The Boreal Spring, Journal of Climate, 26, 45–65, https://doi.org/10.1175/JCLI-D-11-00653.1, 2013.
Pöppelmeier, F., Jeltsch-Thömmes, A., Lippold, J., Joos, F., and Stocker, T. F.: Multi-proxy constraints on Atlantic circulation dynamics since the last ice age, Nature Geosci, 16, 349–356, https://doi.org/10.1038/s41561-023-01140-3, 2023.
Pereira, N. S., Clarke, L. J., Chiessi, C. M., Kilbourne, K. H., Crivellari, S., Cruz, F. W., Campos, J., Yu, T.-L., Shen, C.-C., Kikuchi, R., Pinheiro, B. R., Longo, G. O., Sial, A. N., and Felis, T.: Mid to late 20th century freshening of the western tropical South Atlantic triggered by southward migration of the Intertropical Convergence Zone, Palaeogeography, Palaeoclimatology, Palaeoecology, 597, 111013, https://doi.org/10.1016/j.palaeo.2022.111013, 2022.
Repschläger, J., Zhao, N., Rand, D., Lisiecki, L., Muglia, J., Mulitza, S., Schmittner, A., Cartapanis, O., Bauch, H. A., Schiebel, R., and Haug, G. H.: Active North Atlantic deepwater formation during Heinrich Stadial 1, Quaternary Science Reviews, 270, 107145, https://doi.org/10.1016/j.quascirev.2021.107145, 2021.
Sereno, P. C., Garcea, E. A. A., Jousse, H., Stojanowski, C. M., Saliège, J.-F., Maga, A., Ide, O. A., Knudson, K. J., Mercuri, A. M., Stafford, T. W., Kaye, T. G., Giraudi, C., N'siala, I. M., Cocca, E., Moots, H. M., Dutheil, D. B., and Stivers, J. P.: Lakeside cemeteries in the Sahara: 5000 years of Holocene population and environmental change, PloS one, 3, e2995, https://doi.org/10.1371/journal.pone.0002995, 2008.
Stager, J. C., Ryves, D. B., Chase, B. M., and Pausata, F. S. R.: Catastrophic drought in the Afro-Asian monsoon region during Heinrich event 1, Science (New York, N.Y.), 331, 1299–1302, https://doi.org/10.1126/science.1198322, 2011.
Stanford, J. D., Rohling, E. J., Bacon, S., Roberts, A. P., Grousset, F. E., and Bolshaw, M.: A new concept for the paleoceanographic evolution of Heinrich event 1 in the North Atlantic, Quaternary Science Reviews, 30, 1047–1066, https://doi.org/10.1016/j.quascirev.2011.02.003, 2011.
Wett, S., Rhein, M., Kieke, D., Mertens, C., and Moritz, M.: Meridional Connectivity of a 25‐Year Observational AMOC Record at 47°N, Geophysical Research Letters, 50, https://doi.org/10.1029/2023GL103284, 2023.
Zhang, R. and Delworth, T. L.: Simulated Tropical Response to a Substantial Weakening of the Atlantic Thermohaline Circulation, Journal of Climate, 18, 1853–1860, https://doi.org/10.1175/JCLI3460.1, 2005.
Citation: https://doi.org/10.5194/egusphere-2023-2589-RC2
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 786 | 589 | 43 | 1,418 | 60 | 34 | 33 |
- HTML: 786
- PDF: 589
- XML: 43
- Total: 1,418
- Supplement: 60
- BibTeX: 34
- EndNote: 33
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1