Uncertainty in near-term global surface warming linked to tropical Pacific climate variability

Bordbar, Mohammad Hadi; England, Matthew H.; Gupta, Alex Sen; Santoso, Agus; Taschetto, Andréa S.; Martin, Thomas; Park, Wonsun; Latif, Mojib

doi:10.1038/s41467-019-09761-2

Cited by 23 publications

(13 citation statements)

References 56 publications

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“…Both surface and radiosonde records contain periods in which observed warming is at the upper bound of model-simulated warming (19,41). In addition to its impacts on temperature, multidecadal variability has also contributed to rapid, observed Arctic sea-ice loss (42) and to changes in the strength of the Pacific Walker Circulation (43,44). The presence of such large multidecadal climate variability must be accounted for when using observational data to construct emergent constraints on transient or equilibrium climate sensitivity.…”

Section: Discussionmentioning

confidence: 99%

Natural variability contributes to model–satellite differences in tropical tropospheric warming

Po‐Chedley

Santer

Fueglistaler

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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A long-standing discrepancy exists between general circulation models (GCMs) and satellite observations: The multimodel mean temperature of the midtroposphere (TMT) in the tropics warms at approximately twice the rate of observations. Using a large ensemble of simulations from a single climate model, we find that tropical TMT trends (1979–2018) vary widely and that a subset of realizations are within the range of satellite observations. Realizations with relatively small tropical TMT trends are accompanied by subdued sea-surface warming in the tropical central and eastern Pacific. Observed changes in sea-surface temperature have a similar pattern, implying that the observed tropical TMT trend has been reduced by multidecadal variability. We also assess the latest generation of GCMs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). CMIP6 simulations with muted warming over the central and eastern Pacific also show reduced tropical tropospheric warming. We find that 13% of the model realizations have tropical TMT trends within the observed trend range. These simulations are from models with both small and large climate sensitivity values, illustrating that the magnitude of tropical tropospheric warming is not solely a function of climate sensitivity. For global averages, one-quarter of model simulations exhibit TMT trends in accord with observations. Our results indicate that even on 40-y timescales, natural climate variability is important to consider when comparing observed and simulated tropospheric warming and is sufficiently large to explain TMT trend differences between models and satellite data.

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Section: Discussionmentioning

confidence: 99%

Natural variability contributes to model–satellite differences in tropical tropospheric warming

Po‐Chedley

Santer

Fueglistaler

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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“…Hence, it seems essential to work toward a comprehensive monitoring system based on the size structure of planktons. Incontrovertible evidence for human-induced climate changes has become more frequent (IPCC 2014;Bordbar et al 2015Bordbar et al , 2019, which might have short-and far-reaching implications for the pelagic marine ecosystems across the BUS.…”

Section: Discussionmentioning

confidence: 99%

“…Among different satellite altimetry products, absolute dynamic topography (ADT), defined as the local deviation of sea surface height from the geoid, is chosen and analyzed. The deviation of observed ADT and simulated sea surface height from their areal average over the model domain are computed and termed as dynamic sea level (DSL; Greatbatch 1994;Bordbar et al 2015). The main reason for choosing the DSL comes back to the fact that we considered Boussinesq approximation (i.e., conservation of volume rather than mass) in the model simulation.…”

Section: Methodsmentioning

confidence: 99%

The relation of wind-driven coastal and offshore upwelling in the Benguela Upwelling System

Bordbar

Mohrholz

Schmidt

2021

Journal of Physical Oceanography

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Spatial and temporal variations of nutrient-rich upwelled water across the major eastern boundary upwelling systems are primarily controlled by the surface wind with different, and sometimes contrasting, impacts on coastal upwelling systems driven by alongshore wind and offshore upwelling systems driven by the local wind-stress-curl. Here, concurrently measured wind-fields, satellite-derived Chlorophyll-a concentration along with a state-of-the-art ocean model simulation spanning 2008-2018 are used to investigate the connection between coastal and offshore physical drivers of the Benguela Upwelling System (BUS). Our results indicate that the spatial structure of long-term mean upwelling derived from Ekman theory and the numerical model are fairly consistent across the entire BUS and closely followed by the Chlorophyll-a pattern. The variability of the upwelling from the Ekman theory is proportionally diminished with offshore distance, whereas different and sometimes opposite structures are revealed in the model-derived upwelling. Our result suggests the presence of sub-mesoscale activity (i.e., filaments and eddies) across the entire BUS with a large modulating effect on the wind-stress-curl-driven upwelling off Lüderitz and Walvis Bay. In Kunene and Cape Frio upwelling cells, located in the northern sector of the BUS, the coastal upwelling and open-ocean upwelling frequently alternate each other, whereas they are modulated by the annual cycle and mostly in phase off Walvis Bay. Such a phase relationship appears to be strongly seasonally dependent off Lüderitz and across the southern BUS. Thus, our findings suggest this relationship is far more complex than currently thought and seems to be sensitive to climate changes with short- and far-reaching consequences for this vulnerable marine ecosystem.

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“…Previous debates on the global warming hiatus have made it clear that the equatorial Pacific SST pattern, as measured by SST eq , is an important driver of GSAT to slow down or accelerate the radiatively forced response 1,21,25,30 . Therefore, the evolution of multi-decadal trends in GSAT is expected to reveal a discernible difference between S-and W-models (Fig.…”

mentioning

confidence: 99%

Enhanced warming constrained by past trends in equatorial Pacific sea surface temperature gradient

et al. 2020

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The zonal gradient in the equatorial Pacific sea surface temperature (SST), high in the west and low in the east, is known to be a pacemaker of global warming 1. The zonal SST gradient has strengthened since the mid-20 th century 2 , but the cause is controversial because it is not reproduced by a majority of Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models 3-6 , which instead suggest a weakening of the zonal SST gradient from the past to the future 7. This discrepancy between observations and models has to be reconciled not only for attributing the past climate change but also for assessing Earth's climate sensitivity 8,9. Here we show using large ensemble (LE) simulations by four different climate models, in addition to CMIP5 models, that the intensified trend in the Pacific zonal SST gradient for 1951-2010 can be captured by some realisations, suggesting that it could arise from internal climate variability. Models and members that simulate the past strengthening of the SST gradient in CMIP5 and LE commonly exhibit reversed trends in future projections, when the rate of global-mean temperature rise is likely to amplify by 9-30% with the larger values occurring in low-emission scenarios. Atmosphere-ocean state in the tropical Pacific is characterised by the zonal contrast between high SST in the warm pool and low SST in the cold tongue, tied with the Walker circulation accompanying surface easterlies. This mean state is maintained by the well-known Bjerknes feedback 10 , which acts against radiative heating that homogenises SST zonally. Specifically, equatorial easterlies pile warm water up to the west and cause upwelling to cool the eastern Pacific. The strengthened SST gradient, in turn, amplifies the easterlies by

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Uncertainty in near-term global surface warming linked to tropical Pacific climate variability

Cited by 23 publications

References 56 publications

Natural variability contributes to model–satellite differences in tropical tropospheric warming

Natural variability contributes to model–satellite differences in tropical tropospheric warming

The relation of wind-driven coastal and offshore upwelling in the Benguela Upwelling System

Enhanced warming constrained by past trends in equatorial Pacific sea surface temperature gradient

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