scholarly journals Past, Present, and Future Changes in the Atlantic Meridional Overturning Circulation

2012 ◽  
Vol 93 (11) ◽  
pp. 1663-1676 ◽  
Author(s):  
M. Srokosz ◽  
M. Baringer ◽  
H. Bryden ◽  
S. Cunningham ◽  
T. Delworth ◽  
...  
Keyword(s):  
Climate Change ◽  
Global Climate ◽  
Surface Air Temperature ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Human Populations ◽  
Overturning Circulation ◽  
Intergovernmental Panel ◽  
The Future ◽  
Meridional Overturning

Observations and numerical modeling experiments provide evidence for links between variability in the Atlantic meridional overturning circulation (AMOC) and global climate patterns. Reduction in the strength of the overturning circulation is thought to have played a key role in rapid climate change in the past and may have the potential to significantly influence climate change in the future, as noted in the last two Intergovernmental Panel on Climate Change (IPCC) assessment reports (Houghton et al.; Solomon et al.). Both IPCC reports also highlighted the significant uncertainties that exist regarding the future behavior of the AMOC under global warming. Model results suggest that changes in the AMOC can impact surface air temperature, precipitation patterns, and sea level, particularly in areas bordering the North Atlantic, thus affecting human populations. Here, the current understanding of past, present, and future changes in the AMOC and the effects of such changes on climate are reviewed. The focus is on observations of the AMOC, how the AMOC influences climate, and in what way the AMOC is likely to change over the next few decades and the twenty-first century. The potential for decadal prediction of the AMOC is also discussed. Finally, the outstanding challenges and possible future directions for AMOC research are outlined.

scholarly journals Evaluation of Different Methods to Assess Model Projections of the Future Evolution of the Atlantic Meridional Overturning Circulation

2007 ◽  
Vol 20 (10) ◽  
pp. 2121-2132 ◽  
Author(s):  
Birgit Schneider ◽  
M. Latif ◽  
Andreas Schmittner
Keyword(s):  
Climate Models ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Coupled Models ◽  
Overturning Circulation ◽  
Intergovernmental Panel ◽  
Future Evolution ◽  
The North ◽  
The Future ◽  
Meridional Overturning

Abstract Climate models predict a gradual weakening of the North Atlantic meridional overturning circulation (MOC) during the twenty-first century due to increasing levels of greenhouse gas concentrations in the atmosphere. Using an ensemble of 16 different coupled climate models performed for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), the evolution of the MOC during the twentieth and twenty-first centuries is analyzed by combining model simulations for the IPCC scenarios Twentieth-Century Climate in Coupled Models (20C3M) and Special Report on Emission Scenarios, A1B (SRESA1B). Earlier findings are confirmed that even for the same forcing scenario the model response is spread over a large range. However, no model predicts abrupt changes or a total collapse of the MOC. To reduce the uncertainty of the projections, different weighting procedures are applied to obtain “best estimates” of the future MOC evolution, considering the skill of each model to represent present day hydrographic fields of temperature, salinity, and pycnocline depth as well as observation-based mass transport estimates. Using different methods of weighting the various models together, all produce estimates that the MOC will weaken by 25%–30% from present day values by the year 2100; however, absolute values of the MOC and the degree of reduction differ among the weighting methods.

The Atlantic Meridional Overturning Circulation (AMOC) simulated during interglacials and its impact on climate

2021 ◽  
Author(s):  
Zhiyi Jiang ◽  
Chris Brierley ◽  
David Thornalley ◽  
Sophie Sax
Keyword(s):  
Spatial Structure ◽  
Surface Temperature ◽  
Global Climate ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Last Interglacial ◽  
Overturning Circulation ◽  
Poleward Heat Transport ◽  
Meridional Overturning ◽  
Proxy Reconstructions

<p>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 inforcing, 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 previous simulations from the Palaeoclimate Modelling Intercomparison Project (PMIP), this arose from feedbacks between sea ice and AMOC changes, which also depended on resolution. Here I present aninitial analysis of the recently available PMIP4 simulations. This shows the overall strength of the AMOC does not markedly change between the mid-Holocene and piControl experiments (at least looking at the maximum of the mean meridional mass overturning streamfunction below 500m at 30<sup>o</sup>N and 50<sup>o</sup>N). This is not inconsistent with the proxy reconstructions using sortable silt and Pa/Th for the mid-Holocene. Here we analyse changes in the spatial structure of the meridional overturning circulation, along with their fingerprints on the surface temperature (computed through regression). We then estimate the percentage of the simulated surface temperature changes between the mid-Holocene and pre-industrial period that can be explained by AMOC. Furthermore, the analysis for the changes in the AMOC spatial structure has been extended to see if the same patterns of change hold for the last interglacial. The simulations will be compared to existing proxy reconstructions, as well as new palaeoceanographic reconstructions.</p>

Observed Evidence of a Stable Atlantic Meridional Overturning Circulation since the 1990s

2020 ◽  
Author(s):  
Yao Fu ◽  
Feili Li ◽  
Johannes Karstensen ◽  
N. Penny Holliday ◽  
Chunzai Wang
Keyword(s):  
North Atlantic ◽  
Global Climate ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Distribution Model ◽  
Overturning Circulation ◽  
State Estimate ◽  
The Past ◽  
Stable Partition ◽  
Meridional Overturning

<p>The Atlantic Meridional Overturning Circulation (AMOC) is crucially important in the global climate system due to its role in the meridional heat and freshwater distribution. Model simulations and constructed AMOC indices suggest that the AMOC may have been weakening for decades. However, direct AMOC observations, introduced in 2004 in the subtropics (the RAPID program) and in 2014 in the subpolar North Atlantic (the OSNAP program), are not sufficiently long to capture changes dating back to previous periods. Here we use repeated hydrographic sections in the subtropical and subpolar North Atlantic through the early 1990s to the mid-2010s, combined with a box inverse model that is constrained using satellite altimetry, to analyze hydrographic changes and the AMOC. In combination with a state-of-the-art ocean state estimate, GECCO2, we show that despite dramatic hydrographic changes in the subtropical and subpolar North Atlantic over the past two and half decades, the AMOC has not significantly weakened over the same period. Our hydrography-based estimates also illustrate a remarkably stable partition of the subpolar overturning between the Labrador basin and the eastern subpolar basins on decadal timescales since the 1990s.</p>

scholarly journals Larger Role for Shallow Intermediate Waters in Ocean Circulation

Eos ◽  
2020 ◽  
Vol 101 ◽  
Author(s):  
Sara Pratt
Keyword(s):  
Ocean Circulation ◽  
Global Climate ◽  
Atlantic Meridional Overturning Circulation ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
Intermediate Waters

Water masses formed off southeastern Greenland may contribute more than previously thought to the variability of the Atlantic Meridional Overturning Circulation, which strongly influences global climate.

scholarly journals Latest Pliocene Northern Hemisphere glaciation amplified by intensified Atlantic meridional overturning circulation

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Tatsuya Hayashi ◽  
Toshiro Yamanaka ◽  
Yuki Hikasa ◽  
Masahiko Sato ◽  
Yoshihiro Kuwahara ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Deep Water ◽  
Global Climate ◽  
Atlantic Meridional Overturning Circulation ◽  
North Atlantic Deep Water ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Early Stages ◽  
Meridional Overturning

Abstract The global climate has been dominated by glacial–interglacial variations since the intensification of Northern Hemisphere glaciation 2.7 million years ago. Although the Atlantic meridional overturning circulation has exerted strong influence on recent climatic changes, there is controversy over its influence on Northern Hemisphere glaciation because its deep limb, North Atlantic Deep Water, was thought to have weakened. Here we show that Northern Hemisphere glaciation was amplified by the intensified Atlantic meridional overturning circulation, based on multi-proxy records from the subpolar North Atlantic. We found that the Iceland–Scotland Overflow Water, contributing North Atlantic Deep Water, significantly increased after 2.7 million years ago and was actively maintained even in early stages of individual glacials, in contrast with late stages when it drastically decreased because of iceberg melting. Probably, the active Nordic Seas overturning during the early stages of glacials facilitated the efficient growth of ice sheets and amplified glacial oscillations.

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