Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900

Latif, Mojib; Sun, Jing; Visbeck, Martin; Bordbar, Mohammad Hadi

doi:10.1038/s41558-022-01342-4

Cited by 52 publications

(47 citation statements)

References 90 publications

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“…There is currently no consensus on whether the AMOC has declined since the 1990s (see, for example, Jackson et al, 2022;Latif et al, 2022, for summaries of the debate). Models and proxies suggest a decline (e.g.…”

Section: Subtropical-origin Water and Meridional Overturningmentioning

confidence: 99%

Exceptional freshening and cooling in the eastern subpolar North Atlantic caused by reduced Labrador Sea surface heat loss

Fox

Handmann²,

Schmidt³

et al. 2022

Ocean Sci.

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Abstract. Observations of the eastern subpolar North Atlantic in the 2010s show exceptional freshening and cooling of the upper ocean, peaking in 2016 with the lowest salinities recorded for 120 years. Published theories for the mechanisms driving the freshening include: reduced transport of saltier, warmer surface waters northwards from the subtropics associated with reduced meridional overturning; shifts in the pathways of fresher, cooler surface water from the Labrador Sea driven by changing patterns of wind stress; and the eastward expansion of the subpolar gyre. Using output from a high-resolution hindcast model simulation, we propose that the primary cause of the exceptional freshening and cooling is reduced surface heat loss in the Labrador Sea. Tracking virtual fluid particles in the model backwards from the eastern subpolar North Atlantic between 1990 and 2020 shows the major cause of the freshening and cooling to be an increased outflow of relatively fresh and cold surface waters from the Labrador Sea; with a minor contribution from reduced transport of warmer, saltier surface water northward from the subtropics. The cooling, but not the freshening, produced by these changing proportions of waters of subpolar and subtropical origin is mitigated by reduced along-track heat loss to the atmosphere in the North Atlantic Current. We analyse modelled boundary exchanges and water mass transformation in the Labrador Sea to show that since 2000, while inflows of lighter surface waters remain steady, the increasing output of these waters is due to reduced surface heat loss in the Labrador Sea beginning in the early 2000s. Tracking particles further upstream reveals that the primary source of the increased volume of lighter water transported out of the Labrador Sea is increased recirculation of water, and therefore longer residence times, in the upper 500–1000 m of the subpolar gyre.

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Section: Subtropical-origin Water and Meridional Overturningmentioning

confidence: 99%

Exceptional freshening and cooling in the eastern subpolar North Atlantic caused by reduced Labrador Sea surface heat loss

Fox

Handmann²,

Schmidt³

et al. 2022

Ocean Sci.

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show abstract

“…EC-Earth3-LR and the two models by FGOALS are the exceptions, but they do not provide coherent message about the response to increasing orbital forcing. Therefore, we consider these to be different samples from the same underlying distribution (Latif et al, 2022).…”

Section: Methodsmentioning

confidence: 99%

No changes in overall AMOC strength in interglacial PMIP4 timeslices

Jiang

Brierley

Thornalley

et al. 2022

Preprint

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Abstract. The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism of poleward heat transport and an important part of the global climate system. How it responded to past changes in forcing, such as experienced during Quaternary interglacials, is an intriguing and open question. Previous modelling studies suggest an enhanced AMOC in the mid-Holocene compared to the pre-industrial period. In earlier simulations from the Palaeoclimate Modelling Intercomparison Project (PMIP), this arose from feedbacks between sea ice and AMOC changes, which were dependent on resolution. Here we present an initial analysis of the recently available PMIP4 simulations. The ensemble mean of the PMIP4 models shows the strength of the AMOC does not markedly change between the midHolocene and piControl experiments or between the lig127k and piControl experiments. Therefore, it appears orbital forcing itself does not alter the overall AMOC. We further investigate the coherency of the forced response in AMOC across the two interglacials, along with the strength of the signal, using eight PMIP4 models which performed both interglacial experiments. Only 2 models show a stronger change with the stronger forcing, but those models disagree on the direction of the change. We propose that the strong signals in these 2 models are caused by a combination of forcing and the internal variability. After investigating the AMOC changes in the interglacials, we further explored the impact of AMOC on the climate system, especially on the changes in the simulated surface temperature and precipitation. After identifying the AMOC’s fingerprint on the surface temperature and rainfall, we demonstrate that only a small percentage of the simulated surface climate changes can be attributed to the AMOC. Proxy records during the two interglacial periods paint a similar picture of minimal changes, which fits nicely with the simulated results. Although the overall AMOC strength shows minimal changes, future work is required to explore whether this occurs through compensating variations in the different components of AMOC (such as Iceland-Scotland overflow water). This lines of evidence caution against interpreting reconstructions of past interglacial climate as being driven by AMOC, outside of abrupt events.

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“…The earth has undergone tremendous changes since industrial civilization, and among these, climate change is one of the most obvious phenomena (IPCC, 2022). The average temperature of the earth has raised for nearly 1.5 °C since 1900, which results in many catastrophes such as floods and droughts (Latif et al, 2022). Climate change caused by greenhouse gas emissions (GHGs) is a key issue for sustainable development all over the world (Mooney and Sjogersten, 2022).…”

Section: Editorial On the Research Topic Sustainable Energy Systems W...mentioning

confidence: 99%

Editorial: Sustainable Energy Systems With Policies in China

Chen

Nie²,

Wang³

et al. 2022

Front. Energy Res.

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Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900

Cited by 52 publications

References 90 publications

Exceptional freshening and cooling in the eastern subpolar North Atlantic caused by reduced Labrador Sea surface heat loss

Exceptional freshening and cooling in the eastern subpolar North Atlantic caused by reduced Labrador Sea surface heat loss

No changes in overall AMOC strength in interglacial PMIP4 timeslices

Editorial: Sustainable Energy Systems With Policies in China

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