Historical forcings as main drivers of the Atlantic multidecadal variability in the CESM large ensemble

Bellomo, Katinka; Murphy, Lisa N.; Cane, Mark A.; Clement, A. C.; Polvani, Lorenzo M.

doi:10.1007/s00382-017-3834-3

Cited by 107 publications

(143 citation statements)

References 51 publications

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“…The external forcing of the model's AMV and the lead‐lag relationships between its AMV and AMOC shows that earlier findings (Bellomo et al, ; Murphy et al, ; Tandon & Kushner, ) hold also for simulations initialized from different ocean states. The consequential small role allowed for internal ocean variability in explaining AMOC variations given external forcings ‐historical and prospective‐ has received little attention in the literature so far.…”

Section: Summary Discussion and Conclusionsupporting

confidence: 52%

“…A key issue are the roles of internal variability versus external forcing during the historical period (Knight, ; Ting et al, , ), and the extent of their interaction (Tandon & Kushner, ). A dominant role for external forcing, especially from volcanic eruptions, has for instance been concluded from models, observations, and last‐millennium proxies (e.g., Bellomo et al, , Knudsen et al, , Otterå et al, , Wang et al, ), but the assessment is complicated by the short observational record and the complex spatiotemporal nature of North Atlantic SST variability, making findings controversial.…”

Section: Introductionmentioning

confidence: 99%

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Contrasting the Effects of the 1850–1975 Increase in Sulphate Aerosols from North America and Europe on the Atlantic in the CESM

Undorf

Bollasina

Booth

et al. 2018

Geophysical Research Letters

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The extent and mechanisms of the Atlantic response to the historical (1850–1975) increase of sulphate aerosol emissions from North America and Europe as simulated in eight‐member ensemble experiments with the coupled Community Earth System Model (CESM1)‐Community Atmosphere Model version 5.3 are contrasted. The results show that aerosols from either source cause a long‐term cooling of North Atlantic sea surface temperatures, with the patterns a combination of atmospheric aerosol effects and an aerosol‐induced strengthening of the Atlantic Meridional Overturning Circulation. The response to North American emissions is larger since prevailing winds cause wider aerosol spread over the Atlantic, collocated with climatological cloud cover. The Intertropical Convergence Zone shifts southward affecting tropical precipitation globally. The simulated (multi)decadal components of sea surface temperature and Atlantic Meridional Overturning Circulation variability are furthermore primarily externally forced. The analysis provides novel insights into the mechanisms of aerosol impact on the Atlantic. It suggests that projected further emission reductions will lead to opposite changes.

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Section: Summary Discussion and Conclusionsupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Contrasting the Effects of the 1850–1975 Increase in Sulphate Aerosols from North America and Europe on the Atlantic in the CESM

Undorf

Bollasina

Booth

et al. 2018

Geophysical Research Letters

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“…High correlations between the observed and simulated NASST have been put forward as the key evidence supporting externally forced AMV (Bellomo et al, ; Booth et al, ; Murphy et al, ). Figure a shows the 20‐year low‐pass‐filtered NASST anomalies from HadISST and the LENS ensemble mean.…”

Section: Resultsmentioning

confidence: 99%

Key Role of Internal Ocean Dynamics in Atlantic Multidecadal Variability During the Last Half Century

Kim

Yeager

Danabasoglu

2018

Geophysical Research Letters

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This study presents multiple lines of evidence from observations and model simulations that support a key role for ocean dynamics, rather than external forcings, in Atlantic multidecadal variability (AMV) during the last half century. Observed AMV fingerprints considered here include the low‐frequency spatiotemporal evolution of sea surface temperature, surface heat fluxes, and deep ocean hydrography. While largely absent in the forced response of a large ensemble historical simulations (LENSs), these fingerprints are clearly discernible in a long control simulation where the variability is purely internal. Further evidence derives from initialized decadal prediction simulations, which exhibit much higher skill at predicting the observed AMV of the past 50 years than LENS. The high correlation between the observed AMV and the externally forced version derived from LENS, which has been invoked as evidence for externally driven AMV, is shown to be largely an artifact of concurrent warming since the 1990s.

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“…Many previous studies have consistently attributed observed AMV primarily to internal variability associated with the AMOC (e.g., DelSole et al, ; Knight, ; Ting et al, ; Trenberth & Shea, ; Z. Wu, Huang, et al, ; Zanchettin et al, ). On the other hand, some recent studies have proposed the hypotheses that AMV is primarily a direct response of the North Atlantic SST to either changes in external radiative forcing (e.g., Bellomo et al, ; Bellucci et al, ; Booth et al, ; Murphy et al, ) or stochastic atmospheric forcing (e.g., Cane et al, ; Clement et al, , ), although these views have been questioned (e.g., Drews & Greatbatch, , ; Kim, Yeager, & Danabasoglu, ; O'Reilly et al, ; Sun et al, ; Yan et al, , , ; Zhang, ; Zhang et al, , ). The traditional AMV index, which is based on the North Atlantic SST anomalies as first proposed by Enfield et al (), is convenient to use due to the availability of SST records over the instrumental period and the close linkage of SST with climate impacts.…”

Section: Introductionmentioning

confidence: 99%

A Review of the Role of the Atlantic Meridional Overturning Circulation in Atlantic Multidecadal Variability and Associated Climate Impacts

Zhang

Sutton

Danabasoglu

et al. 2019

Reviews of Geophysics

366

362

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By synthesizing recent studies employing a wide range of approaches (modern observations, paleo reconstructions, and climate model simulations), this paper provides a comprehensive review of the linkage between multidecadal Atlantic Meridional Overturning Circulation (AMOC) variability and Atlantic Multidecadal Variability (AMV) and associated climate impacts. There is strong observational and modeling evidence that multidecadal AMOC variability is a crucial driver of the observed AMV and associated climate impacts and an important source of enhanced decadal predictability and prediction skill. The AMOC‐AMV linkage is consistent with observed key elements of AMV. Furthermore, this synthesis also points to a leading role of the AMOC in a range of AMV‐related climate phenomena having enormous societal and economic implications, for example, Intertropical Convergence Zone shifts; Sahel and Indian monsoons; Atlantic hurricanes; El Niño–Southern Oscillation; Pacific Decadal Variability; North Atlantic Oscillation; climate over Europe, North America, and Asia; Arctic sea ice and surface air temperature; and hemispheric‐scale surface temperature. Paleoclimate evidence indicates that a similar linkage between multidecadal AMOC variability and AMV and many associated climate impacts may also have existed in the preindustrial era, that AMV has enhanced multidecadal power significantly above a red noise background, and that AMV is not primarily driven by external forcing. The role of the AMOC in AMV and associated climate impacts has been underestimated in most state‐of‐the‐art climate models, posing significant challenges but also great opportunities for substantial future improvements in understanding and predicting AMV and associated climate impacts.

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Historical forcings as main drivers of the Atlantic multidecadal variability in the CESM large ensemble

Cited by 107 publications

References 51 publications

Contrasting the Effects of the 1850–1975 Increase in Sulphate Aerosols from North America and Europe on the Atlantic in the CESM

Contrasting the Effects of the 1850–1975 Increase in Sulphate Aerosols from North America and Europe on the Atlantic in the CESM

Key Role of Internal Ocean Dynamics in Atlantic Multidecadal Variability During the Last Half Century

A Review of the Role of the Atlantic Meridional Overturning Circulation in Atlantic Multidecadal Variability and Associated Climate Impacts

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