Detectability of an AMOC Decline in Current and Projected Climate Changes

Lobelle, Delphine; Beaulieu, Claudie; Livina, Valerie N.; Sévellec, Florian; Frajka‐Williams, Eleanor

doi:10.1029/2020gl089974

Cited by 20 publications

(17 citation statements)

References 51 publications

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“…Our simulation shows that the AMOC could reduce its impact on CO 2 uptake in subsequent centuries relative to this century. The AMOC strength is predicted to decrease from 31 Sverdrup (Sv) to 5 Sv by the year 2300 (Figure S1 in Supporting Information S1), consistent with other climate projections for AMOC slowdown (Collins et al., 2013; Lobelle et al., 2020; Meehl et al., 2013). Such a response will reduce the downward transport of CO 2 into the deep ocean, increasing p CO 2 ocn in the North Atlantic (Figure 3c).…”

Section: Discussionsupporting

confidence: 81%

Multi‐Century Changes in the Ocean Carbon Cycle Controlled by the Tropical Oceans and the Southern Ocean

Chikamoto

DiNezio

2021

Global Biogeochemical Cycles

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The oceanic absorption of anthropogenic carbon dioxide (CO2) is expected to continue in the following centuries, but the processes driving these changes remain uncertain. We studied these processes in a simulation of future changes in global climate and the carbon cycle following the RCP8.5 high emission scenario. The simulation shows increasing oceanic uptake of anthropogenic CO2 peaking towards the year 2080 and then slowing down but remaining significant in the period up to the year 2300. These multi‐century changes in uptake are dominated by changes in sea‐air CO2 fluxes in the tropical and southern oceans. In the tropics, reductions in upwelling and vertical gradients of dissolved carbon will reduce the vertical advection of carbon‐rich thermocline waters, suppressing natural outgassing of CO2. In the Southern Ocean, the upwelling of waters with relatively low dissolved carbon keeps the surface carbon relatively low, enhancing the uptake of CO2 in the next centuries. The slowdown in CO2 uptake in the subsequent centuries is caused by the decrease in CO2 solubility and storage capacity in the ocean due to ocean warming and changes in carbon chemistry. A collapse of the Atlantic Meridional Overturning Circulation (AMOC) predicted for the next century causes a substantial reduction in the uptake of anthropogenic CO2. In sum, predicting multi‐century changes in the global carbon cycle depends on future changes in carbon chemistry along with changes in oceanic and atmospheric circulations in the Southern and tropical oceans, together with a potential collapse of the AMOC.

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Section: Discussionsupporting

confidence: 81%

Multi‐Century Changes in the Ocean Carbon Cycle Controlled by the Tropical Oceans and the Southern Ocean

Chikamoto

DiNezio

2021

Global Biogeochemical Cycles

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“…12 However, the new generation of models from the 6th phase (CMIP6) do not exhibit in their ensemble mean a significant AMOC weakening trend over the same period. [14][15][16] While the risk of an abrupt collapse of the AMOC has been estimated in the SROCC report 12 as "very unlikely" over this century, some CMIP5 models have shown that part of the AMOC system, namely the SPG, could experience a large change in less than a decade. 17 Indeed, the SPG has been recently recognized as a tipping element of the climate system [18][19][20] that can shift from the current steady state to another one on a far shorter timescale than the AMOC.…”

Section: Introductionmentioning

confidence: 99%

On the risk of abrupt changes in the North Atlantic subpolar gyre in CMIP6 models

Swingedouw

Bily

Esquerdo

et al. 2021

Annals of the New York Academy of Sciences

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CMIP5 models have been shown to exhibit rapid cooling events in their projections of the North Atlantic subpolar gyre. Here, we analyze the CMIP6 archive, searching for such rapid cooling events in the new generation of models. Four models out of 35 exhibit such instabilities. The climatic impacts of these events are large on decadal timescales, with a substantial effect on surface temperature over Europe, precipitation pattern in the tropics-most notably the Sahel and Amazon regions-and a possible impact on the mean atmospheric circulation. The mechanisms leading to these events are related to the collapse of deep convection in the subpolar gyre, modifying profoundly the oceanic circulation. Analysis of stratification in the subpolar gyre as compared with observations highlights that the biases of the models explain relatively well the spread in their projections of surface temperature trends: models showing the smallest stratification biases over the recent period also show the weakest warming trends. The models exhibiting abrupt cooling rank among the 11 best models for this stratification indicator, leading to a risk of encountering an abrupt cooling event of up to 36.4%, slightly lower than the 45.5% estimated in CMIP5 models.

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“…Since then, the RAPID array has shown a slight increase in the AMOC, and the weakening trend over 2004-2020 is not significant at the 95% level anymore (Moat et al, 2020). The issue of detectability of AMOC changes from short term series is indeed a serious one, and a detection analysis revealed that a median of 24-43 years (depending on the choices for internal variability) might be necessary to extract any significant trend in the RAPID dataset, which brings us to 2028 at least if we use the RAPID array (Lobelle et al, 2020).…”

Section: What Do the Latest Observations Tell Us? The Key Role Of Tim...mentioning

confidence: 99%

AMOC Recent and Future Trends: A Crucial Role for Oceanic Resolution and Greenland Melting?

et al. 2022

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The Atlantic Meridional Overturning Circulation (AMOC) is a crucial element of the Earth climate. It is a complex circulation system difficult to monitor and to model. There is considerable debate regarding its evolution over the last century as well as large uncertainty about its fate at the end of this century. We depict here the progress since the IPCC SROCC report, offering an update of its chapter 6.7. We also show new results from a high-resolution ocean model and a CMIP6 model to investigate the impact of Greenland Ice Sheet (GrIS) melting, a key uncertainty for past and future AMOC changes. The ocean-only simulation at 1/24° resolution in the Arctic-North Atlantic Ocean performed over the period 2004–2016 indicates that the spread of the Greenland freshwater runoff toward the center of the Labrador Sea, where oceanic convection occurs, seems larger in this model than in a CMIP6 model. Potential explanations are related to the model spatial resolution and the representation of mesoscale processes, which more realistically transport the freshwater released around the shelves and, through eddies, provides strong lateral exchanges between the fine-scale boundary current and the convective basin in the Labrador Sea. The larger freshening of the Labrador Sea in the high-resolution model then strongly affects deep convection activity. In the simulation including GrIS melting, the AMOC weakens by about 2 Sv after only 13 years, far more strongly than what is found in the CMIP6 model. This difference raises serious concerns on the ability of CMIP6 models to correctly assess the potential impact of GrIS melting on the AMOC changes over the last few decades as well as on its future fate. To gain confidence in the GrIS freshwater impacts on climate simulations and therefore in AMOC projections, urgent progress should be made on the parameterization of mesoscale processes in ocean models.

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Detectability of an AMOC Decline in Current and Projected Climate Changes

Cited by 20 publications

References 51 publications

Multi‐Century Changes in the Ocean Carbon Cycle Controlled by the Tropical Oceans and the Southern Ocean

Multi‐Century Changes in the Ocean Carbon Cycle Controlled by the Tropical Oceans and the Southern Ocean

On the risk of abrupt changes in the North Atlantic subpolar gyre in CMIP6 models

AMOC Recent and Future Trends: A Crucial Role for Oceanic Resolution and Greenland Melting?

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