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1

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Drier tropical and subtropical Southern Hemisphere in the mid-Pliocene Warm Period

Pontes, Gabriel M. ; Wainer, Ilana ; Taschetto, Andréa S. ; [et al.]

Springer Science and Business Media LLC ; 2020

In: Scientific Reports Vol. 10, No. 1 ( 2020-08-10)

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In: Scientific Reports, Springer Science and Business Media LLC, Vol. 10, No. 1 ( 2020-08-10)

Abstract: Thermodynamic arguments imply that global mean rainfall increases in a warmer atmosphere; however, dynamical effects may result in more significant diversity of regional precipitation change. Here we investigate rainfall changes in the mid-Pliocene Warm Period (~ 3 Ma), a time when temperatures were 2–3ºC warmer than the pre-industrial era, using output from the Pliocene Model Intercomparison Projects phases 1 and 2 and sensitivity climate model experiments. In the Mid-Pliocene simulations, the higher rates of warming in the northern hemisphere create an interhemispheric temperature gradient that enhances the southward cross-equatorial energy flux by up to 48%. This intensified energy flux reorganizes the atmospheric circulation leading to a northward shift of the Inter-Tropical Convergence Zone and a weakened and poleward displaced Southern Hemisphere Subtropical Convergences Zones. These changes result in drier-than-normal Southern Hemisphere tropics and subtropics. The evaluation of the mid-Pliocene adds a constraint to possible future warmer scenarios associated with differing rates of warming between hemispheres.

Type of Medium: Online Resource

ISSN: 2045-2322

URL: Article

DOI: 10.1038/s41598-020-68884-5

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2020

detail.hit.zdb_id: 2615211-3

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Mid-Pliocene El Niño/Southern Oscillation suppressed by Pacific intertropical convergence zone shift

Pontes, Gabriel M. ; Taschetto, Andréa S. ; Sen Gupta, Alex ; [et al.]

Springer Science and Business Media LLC ; 2022

In: Nature Geoscience Vol. 15, No. 9 ( 2022-09), p. 726-734

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In: Nature Geoscience, Springer Science and Business Media LLC, Vol. 15, No. 9 ( 2022-09), p. 726-734

Type of Medium: Online Resource

ISSN: 1752-0894 , 1752-0908

URL: Article

DOI: 10.1038/s41561-022-00999-y

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2022

detail.hit.zdb_id: 2396648-8

detail.hit.zdb_id: 2405323-5

SSG: 16,13

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Lessons from a high-CO〈sub〉2〈/sub〉 world: an ocean view from ∼ 3 million years ago

McClymont, Erin L. ; Ford, Heather L. ; Ho, Sze Ling ; [et al.]

Copernicus GmbH ; 2020

In: Climate of the Past Vol. 16, No. 4 ( 2020-08-27), p. 1599-1615

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In: Climate of the Past, Copernicus GmbH, Vol. 16, No. 4 ( 2020-08-27), p. 1599-1615

Abstract: Abstract. A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205±0.01 Ma) when atmospheric CO2 exceeded pre-industrial concentrations, but were similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial values, by ∼2.3 ∘C for the combined proxy data (foraminifera Mg∕Ca and alkenones), or by ∼3.2–3.4 ∘C (alkenones only). Compared to the pre-industrial period, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low-CO2 emission scenarios, surface ocean warming may be expected to exceed model projections and will be accentuated in the higher latitudes.

Type of Medium: Online Resource

ISSN: 1814-9332

URL: Article

DOI: 10.5194/cp-16-1599-2020

DOI: 10.5194/cp-16-1599-2020-supplement

Language: English

Publisher: Copernicus GmbH

Publication Date: 2020

detail.hit.zdb_id: 2217985-9

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4

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The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity

Haywood, Alan M. ; Tindall, Julia C. ; Dowsett, Harry J. ; [et al.]

Copernicus GmbH ; 2020

In: Climate of the Past Vol. 16, No. 6 ( 2020-11-04), p. 2095-2123

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In: Climate of the Past, Copernicus GmbH, Vol. 16, No. 6 ( 2020-11-04), p. 2095-2123

Abstract: Abstract. The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ∼400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.7 and 5.2 ∘C relative to the pre-industrial era with a multi-model mean value of 3.2 ∘C. Annual mean total precipitation rates increase by 7 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases by 4.3 ∘C over land and 2.8 ∘C over the oceans. There is a clear pattern of polar amplification with warming polewards of 60∘ N and 60∘ S exceeding the global mean warming by a factor of 2.3. In the Atlantic and Pacific oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. There is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (equilibrium climate sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble Earth system response to a doubling of CO2 (including ice sheet feedbacks) is 67 % greater than ECS; this is larger than the increase of 47 % obtained from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea surface temperatures are used to assess model estimates of ECS and give an ECS range of 2.6–4.8 ∘C. This result is in general accord with the ECS range presented by previous Intergovernmental Panel on Climate Change (IPCC) Assessment Reports.

Type of Medium: Online Resource

ISSN: 1814-9332

URL: Article

DOI: 10.5194/cp-16-2095-2020

DOI: 10.5194/cp-16-2095-2020-supplement

Language: English

Publisher: Copernicus GmbH

Publication Date: 2020

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5

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Highly restricted near‐surface permafrost extent during the mid-Pliocene warm period

Guo, Donglin ; Wang, Huijun ; Romanovsky, Vladimir E. ; [et al.]

Proceedings of the National Academy of Sciences ; 2023

In: Proceedings of the National Academy of Sciences Vol. 120, No. 36 ( 2023-09-05)

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In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 120, No. 36 ( 2023-09-05)

Abstract: Accurate understanding of permafrost dynamics is critical for evaluating and mitigating impacts that may arise as permafrost degrades in the future; however, existing projections have large uncertainties. Studies of how permafrost responded historically during Earth’s past warm periods are helpful in exploring potential future permafrost behavior and to evaluate the uncertainty of future permafrost change projections. Here, we combine a surface frost index model with outputs from the second phase of the Pliocene Model Intercomparison Project to simulate the near‐surface (~3 to 4 m depth) permafrost state in the Northern Hemisphere during the mid-Pliocene warm period (mPWP, ~3.264 to 3.025 Ma). This period shares similarities with the projected future climate. Constrained by proxy-based surface air temperature records, our simulations demonstrate that near‐surface permafrost was highly spatially restricted during the mPWP and was 93 ± 3% smaller than the preindustrial extent. Near‐surface permafrost was present only in the eastern Siberian uplands, Canadian high Arctic Archipelago, and northernmost Greenland. The simulations are similar to near‐surface permafrost changes projected for the end of this century under the SSP5-8.5 scenario and provide a perspective on the potential permafrost behavior that may be expected in a warmer world.

Type of Medium: Online Resource

ISSN: 0027-8424 , 1091-6490

URL: Article

DOI: 10.1073/pnas.2301954120

RVK:

TA 1000

RVK:

WA 15000

Language: English

Publisher: Proceedings of the National Academy of Sciences

Publication Date: 2023

detail.hit.zdb_id: 209104-5

detail.hit.zdb_id: 1461794-8

SSG: 11

SSG: 12

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6

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Reduced El Niño variability in the mid-Pliocene according to the PlioMIP2 ensemble

Oldeman, Arthur M. ; Baatsen, Michiel L. J. ; von der Heydt, Anna S. ; [et al.]

Copernicus GmbH ; 2021

In: Climate of the Past Vol. 17, No. 6 ( 2021-12-01), p. 2427-2450

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In: Climate of the Past, Copernicus GmbH, Vol. 17, No. 6 ( 2021-12-01), p. 2427-2450

Abstract: Abstract. The mid-Pliocene warm period (3.264–3.025 Ma) is the most recent geological period during which atmospheric CO2 levels were similar to recent historical values (∼400 ppm). Several proxy reconstructions for the mid-Pliocene show highly reduced zonal sea surface temperature (SST) gradients in the tropical Pacific Ocean, indicating an El Niño-like mean state. However, past modelling studies do not show these highly reduced gradients. Efforts to understand mid-Pliocene climate dynamics have led to the Pliocene Model Intercomparison Project (PlioMIP). Results from the first phase (PlioMIP1) showed clear El Niño variability (albeit significantly reduced) and did not show the greatly reduced time-mean zonal SST gradient suggested by some of the proxies. In this work, we study El Niño–Southern Oscillation (ENSO) variability in the PlioMIP2 ensemble, which consists of additional global coupled climate models and updated boundary conditions compared to PlioMIP1. We quantify ENSO amplitude, period, spatial structure and “flavour”, as well as the tropical Pacific annual mean state in mid-Pliocene and pre-industrial simulations. Results show a reduced ENSO amplitude in the model-ensemble mean (−24 %) with respect to the pre-industrial, with 15 out of 17 individual models showing such a reduction. Furthermore, the spectral power of this variability considerably decreases in the 3–4-year band. The spatial structure of the dominant empirical orthogonal function shows no particular change in the patterns of tropical Pacific variability in the model-ensemble mean, compared to the pre-industrial. Although the time-mean zonal SST gradient in the equatorial Pacific decreases for 14 out of 17 models (0.2 ∘C reduction in the ensemble mean), there does not seem to be a correlation with the decrease in ENSO amplitude. The models showing the most “El Niño-like” mean state changes show a similar ENSO amplitude to that in the pre-industrial reference, while models showing more “La Niña-like” mean state changes generally show a large reduction in ENSO variability. The PlioMIP2 results show a reasonable agreement with both time-mean proxies indicating a reduced zonal SST gradient and reconstructions indicating a reduced, or similar, ENSO variability.

Type of Medium: Online Resource

ISSN: 1814-9332

URL: Article

DOI: 10.5194/cp-17-2427-2021

DOI: 10.5194/cp-17-2427-2021-supplement

Language: English

Publisher: Copernicus GmbH

Publication Date: 2021

detail.hit.zdb_id: 2217985-9

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7

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Evaluation of Arctic warming in mid-Pliocene climate simulations

de Nooijer, Wesley ; Zhang, Qiong ; Li, Qiang ; [et al.]

Copernicus GmbH ; 2020

In: Climate of the Past Vol. 16, No. 6 ( 2020-11-23), p. 2325-2341

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In: Climate of the Past, Copernicus GmbH, Vol. 16, No. 6 ( 2020-11-23), p. 2325-2341

Abstract: Abstract. Palaeoclimate simulations improve our understanding of the climate, inform us about the performance of climate models in a different climate scenario, and help to identify robust features of the climate system. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), derived from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The PlioMIP2 ensemble simulates Arctic (60–90∘ N) annual mean surface air temperature (SAT) increases of 3.7 to 11.6 ∘C compared to the pre-industrial period, with a multi-model mean (MMM) increase of 7.2 ∘C. The Arctic warming amplification ratio relative to global SAT anomalies in the ensemble ranges from 1.8 to 3.1 (MMM is 2.3). Sea ice extent anomalies range from −3.0 to -10.4×106 km2, with a MMM anomaly of -5.6×106 km2, which constitutes a decrease of 53 % compared to the pre-industrial period. The majority (11 out of 16) of models simulate summer sea-ice-free conditions (≤1×106 km2) in their mPWP simulation. The ensemble tends to underestimate SAT in the Arctic when compared to available reconstructions, although the degree of underestimation varies strongly between the simulations. The simulations with the highest Arctic SAT anomalies tend to match the proxy dataset in its current form better. The ensemble shows some agreement with reconstructions of sea ice, particularly with regard to seasonal sea ice. Large uncertainties limit the confidence that can be placed in the findings and the compatibility of the different proxy datasets. We show that while reducing uncertainties in the reconstructions could decrease the SAT data–model discord substantially, further improvements are likely to be found in enhanced boundary conditions or model physics. Lastly, we compare the Arctic warming in the mPWP to projections of future Arctic warming and find that the PlioMIP2 ensemble simulates greater Arctic amplification than CMIP5 future climate simulations and an increase instead of a decrease in Atlantic Meridional Overturning Circulation (AMOC) strength compared to pre-industrial period. The results highlight the importance of slow feedbacks in equilibrium climate simulations, and that caution must be taken when using simulations of the mPWP as an analogue for future climate change.

Type of Medium: Online Resource

ISSN: 1814-9332

URL: Article

DOI: 10.5194/cp-16-2325-2020

DOI: 10.5194/cp-16-2325-2020-supplement

Language: English

Publisher: Copernicus GmbH

Publication Date: 2020

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8

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Unraveling the mechanisms and implications of a stronger mid-Pliocene Atlantic Meridional Overturning Circulation (AMOC) in PlioMIP2

Weiffenbach, Julia E. ; Baatsen, Michiel L. J. ; Dijkstra, Henk A. ; [et al.]

Copernicus GmbH ; 2023

In: Climate of the Past Vol. 19, No. 1 ( 2023-01-09), p. 61-85

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In: Climate of the Past, Copernicus GmbH, Vol. 19, No. 1 ( 2023-01-09), p. 61-85

Abstract: Abstract. The mid-Pliocene warm period (3.264–3.025 Ma) is the most recent geological period in which the atmospheric CO2 concentration was approximately equal to the concentration we measure today (ca. 400 ppm). Sea surface temperature (SST) proxies indicate above-average warming over the North Atlantic in the mid-Pliocene with respect to the pre-industrial period, which may be linked to an intensified Atlantic Meridional Overturning Circulation (AMOC). Earlier results from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) show that the ensemble simulates a stronger AMOC in the mid-Pliocene than in the pre-industrial. However, no consistent relationship between the stronger mid-Pliocene AMOC and either the Atlantic northward ocean heat transport (OHT) or average North Atlantic SSTs has been found. In this study, we look further into the drivers and consequences of a stronger AMOC in mid-Pliocene compared to pre-industrial simulations in PlioMIP2. We find that all model simulations with a closed Bering Strait and Canadian Archipelago show reduced freshwater transport from the Arctic Ocean into the North Atlantic. This contributes to an increase in salinity in the subpolar North Atlantic and Labrador Sea that can be linked to the stronger AMOC in the mid-Pliocene. To investigate the dynamics behind the ensemble's variable response of the total Atlantic OHT to the stronger AMOC, we separate the Atlantic OHT into two components associated with either the overturning circulation or the wind-driven gyre circulation. While the ensemble mean of the overturning component is increased significantly in magnitude in the mid-Pliocene, it is partly compensated by a reduction in the gyre component in the northern subtropical gyre region. This indicates that the lack of relationship between the total OHT and AMOC is due to changes in OHT by the subtropical gyre. The overturning and gyre components should therefore be considered separately to gain a more complete understanding of the OHT response to a stronger mid-Pliocene AMOC. In addition, we show that the AMOC exerts a stronger influence on North Atlantic SSTs in the mid-Pliocene than in the pre-industrial, providing a possible explanation for the improved agreement of the PlioMIP2 ensemble mean SSTs with reconstructions in the North Atlantic.

Type of Medium: Online Resource

ISSN: 1814-9332

URL: Article

DOI: 10.5194/cp-19-61-2023

DOI: 10.5194/cp-19-61-2023-supplement

Language: English

Publisher: Copernicus GmbH

Publication Date: 2023

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9

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Past terrestrial hydroclimate sensitivity controlled by Earth system feedbacks

Feng, Ran ; Bhattacharya, Tripti ; Otto-Bliesner, Bette L. ; [et al.]

Springer Science and Business Media LLC ; 2022

In: Nature Communications Vol. 13, No. 1 ( 2022-03-14)

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In: Nature Communications, Springer Science and Business Media LLC, Vol. 13, No. 1 ( 2022-03-14)

Abstract: Despite tectonic conditions and atmospheric CO 2 levels ( pCO 2 ) similar to those of present-day, geological reconstructions from the mid-Pliocene (3.3-3.0 Ma) document high lake levels in the Sahel and mesic conditions in subtropical Eurasia, suggesting drastic reorganizations of subtropical terrestrial hydroclimate during this interval. Here, using a compilation of proxy data and multi-model paleoclimate simulations, we show that the mid-Pliocene hydroclimate state is not driven by direct CO 2 radiative forcing but by a loss of northern high-latitude ice sheets and continental greening. These ice sheet and vegetation changes are long-term Earth system feedbacks to elevated pCO 2 . Further, the moist conditions in the Sahel and subtropical Eurasia during the mid-Pliocene are a product of enhanced tropospheric humidity and a stationary wave response to the surface warming pattern, which varies strongly with land cover changes. These findings highlight the potential for amplified terrestrial hydroclimate responses over long timescales to a sustained CO 2 forcing.

Type of Medium: Online Resource

ISSN: 2041-1723

URL: Article

DOI: 10.1038/s41467-022-28814-7

Language: English

Publisher: Springer Science and Business Media LLC

Publication Date: 2022

detail.hit.zdb_id: 2553671-0

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10

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Mid-Pliocene Atlantic Meridional Overturning Circulation simulated in PlioMIP2

Zhang, Zhongshi ; Li, Xiangyu ; Guo, Chuncheng ; [et al.]

Copernicus GmbH ; 2021

In: Climate of the Past Vol. 17, No. 1 ( 2021-02-25), p. 529-543

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In: Climate of the Past, Copernicus GmbH, Vol. 17, No. 1 ( 2021-02-25), p. 529-543

Abstract: Abstract. In the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2), coupled climate models have been used to simulate an interglacial climate during the mid-Piacenzian warm period (mPWP; 3.264 to 3.025 Ma). Here, we compare the Atlantic Meridional Overturning Circulation (AMOC), poleward ocean heat transport and sea surface warming in the Atlantic simulated with these models. In PlioMIP2, all models simulate an intensified mid-Pliocene AMOC. However, there is no consistent response in the simulated Atlantic ocean heat transport nor in the depth of the Atlantic overturning cell. The models show a large spread in the simulated AMOC maximum, the Atlantic ocean heat transport and the surface warming in the North Atlantic. Although a few models simulate a surface warming of ∼ 8–12 ∘C in the North Atlantic, similar to the reconstruction from Pliocene Research, Interpretation and Synoptic Mapping (PRISM) version 4, most models appear to underestimate this warming. The large model spread and model–data discrepancies in the PlioMIP2 ensemble do not support the hypothesis that an intensification of the AMOC, together with an increase in northward ocean heat transport, is the dominant mechanism for the mid-Pliocene warm climate over the North Atlantic.

Type of Medium: Online Resource

ISSN: 1814-9332

URL: Article

DOI: 10.5194/cp-17-529-2021

Language: English

Publisher: Copernicus GmbH

Publication Date: 2021

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