Assessment of time of emergence of anthropogenic deoxygenation and warming: insights from a CESM simulation from 850 to 2100 CE

Abstract. Marine deoxygenation and anthropogenic ocean warming are observed and projected to aggravate under continued greenhouse gas emissions. These changes potentially adversely affect the functioning and services of marine ecosystems. A key question is whether marine ecosystems are already or will soon be exposed to environmental conditions not experienced during the last millennium. We find that anthropogenic deoxygenation and warming in the thermocline have today already left the bounds of natural variability in respectively 60 % and 90 % of total ocean area in a forced simulation with the Community Earth System Model (CESM) over the period 850 to 2100. Natural variability is assessed from last millennium (850–1800) results considering forcing from explosive volcanic eruptions, solar irradiance, and greenhouse gases in addition to internal, chaotic variability. Control simulations are typically used to estimate variability. However, natural variability in oxygen (O2) and temperature (T) are systematically larger than internal variability (e.g. the latter amounts to 20 % for T and 60 % for O2 in the thermocline), rendering such estimates of natural variability to be biased low. Results suggest that anthropogenic change in apparent oxygen utilisation (AOU) and in O2 solubility (O2,sol) are earlier detectable by measurements than in O2 in the tropical thermocline, where biological and solubility-driven O2 changes counteract each other. Both natural variability and change in AOU are predominantly driven by variations in circulation with a smaller role for productivity. Ventilation becomes more vigorous in the tropical thermocline by the end of the 21st century, whereas ideal age in deep waters increases by more than 200 years until 2100. Different methodological choices are compared and the time for an anthropogenic signal to emergence (ToE) is earlier in many thermocline regions when using variability from a short period, the control, or estimates from the industrial period instead variability from the last millennium. Our results highlight that published methods lead to deviations in ToE estimates, calling for a careful quantification of variability and that realised anthropogenic change exceeds natural variations in many regions.

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Assessment of time of emergence of anthropogenic deoxygenation and warming: insights from a CESM simulation from 850 to 2100 CE

Biogeosciences ◽

10.5194/bg-16-1755-2019 ◽

2019 ◽

Vol 16 (8) ◽

pp. 1755-1780 ◽

Cited By ~ 2

Author(s):

Angélique Hameau ◽

Juliette Mignot ◽

Fortunat Joos

Keyword(s):

Volcanic Eruptions ◽

Internal Variability ◽

Marine Ecosystems ◽

Natural Variability ◽

Last Millennium ◽

Methodological Choices ◽

Control Simulation ◽

Deep Waters ◽

Variability Level ◽

Community Earth System Model

Abstract. Marine deoxygenation and anthropogenic ocean warming are observed and projected to intensify in the future. These changes potentially impact the functions and services of marine ecosystems. A key question is whether marine ecosystems are already or will soon be exposed to environmental conditions not experienced during the last millennium. Using a forced simulation with the Community Earth System Model (CESM) over the period 850 to 2100, we find that anthropogenic deoxygenation and warming in the thermocline exceeded natural variability in, respectively, 60 % and 90 % of total ocean area. Control simulations are typically used to estimate the pre-industrial variability level. However, the natural variability of oxygen (O2) and temperature (T) inferred from the last millennium period is systematically larger than the internal variability simulated in the corresponding control simulation. This renders natural variability from control simulations to be biased towards low estimates. Here, natural variability is assessed from the last millennium period (850–1800 CE), thus considering the response to forcing from explosive volcanic eruptions, solar irradiance and greenhouse gases in addition to internal, chaotic variability. Results suggest that in the tropical thermocline, where biological and solubility-driven O2 changes counteract each other, anthropogenic changes in apparent oxygen utilisation (AOU) and in O2 solubility (O2,sol) are detectable earlier than O2 changes. Both natural variability and change in AOU are predominantly driven by variations in circulation with a smaller role for productivity. By the end of the 21st century, ventilation becomes more vigorous in the tropical thermocline, whereas ideal age in deep waters increases by more than 200 years relative to the pre-industrial period. Different methodological choices are compared and the time for an anthropogenic signal to emerge (ToE) is earlier in many thermocline regions when using variability from a shorter period, from the control simulation or estimates from the industrial period instead of the variability from the last millennium. Our results highlight that published methods may lead to deviations in ToE estimates, calling for a careful quantification of variability. They also highlight that realised anthropogenic change exceeds natural variations in many regions.

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How Do Volcanic Eruptions Influence Decadal Megadroughts over Eastern China?

Journal of Climate ◽

10.1175/jcli-d-19-0394.1 ◽

2020 ◽

Vol 33 (19) ◽

pp. 8195-8207 ◽

Cited By ~ 1

Author(s):

Liang Ning ◽

Kefan Chen ◽

Jian Liu ◽

Zhengyu Liu ◽

Mi Yan ◽

...

Keyword(s):

Asian Summer Monsoon ◽

Eastern China ◽

Volcanic Eruptions ◽

Internal Variability ◽

Last Millennium ◽

Decadal Scale ◽

Community Earth System Model ◽

Sea Surface Temperature Anomalies ◽

Asian Summer ◽

The Western Pacific

AbstractThe influence and mechanism of volcanic eruptions on decadal megadroughts over eastern China during the last millennium were investigated using a control (CTRL) and five volcanic eruption sensitivity experiments (VOLC) from the Community Earth System Model (CESM) Last Millennium Ensemble (LME) archive. The decadal megadroughts associated with the failures of the East Asian summer monsoon (EASM) are associated with a meridional tripole of sea surface temperature anomalies (SSTAs) in the western Pacific from the equator to high latitudes, suggestive of a decadal-scale internal mode of variability that emerges from empirical orthogonal function (EOF) analysis. Composite analyses further showed that, on interannual time scales, within a decade after an eruption the megadrought was first enhanced but then weakened, due to the change from an El Niño state to a La Niña state. The impacts of volcanic eruptions on the magnitudes of megadroughts are superposed on internal variability. Therefore, the evolution of decadal megadroughts coinciding with strong volcanic eruptions demonstrate that the impacts of internal variability and external forcing can combine to influence hydroclimate.

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Climate and carbon cycle dynamics in a CESM simulation from 850 to 2100 CE

Earth System Dynamics ◽

10.5194/esd-6-411-2015 ◽

2015 ◽

Vol 6 (2) ◽

pp. 411-434 ◽

Cited By ~ 32

Author(s):

F. Lehner ◽

F. Joos ◽

C. C. Raible ◽

J. Mignot ◽

A. Born ◽

...

Keyword(s):

Carbon Cycle ◽

Volcanic Eruptions ◽

Internal Variability ◽

Total Solar Irradiance ◽

Last Millennium ◽

Time Period ◽

Decadal Scale ◽

Current Century ◽

Community Earth System Model ◽

Ocean Carbon

Abstract. Under the protocols of phase 3 of the Paleoclimate Modelling Intercomparison Project, a number of simulations were produced that provide a range of potential climate evolutions from the last millennium to the end of the current century. Here, we present the first simulation with the Community Earth System Model (CESM), which includes an interactive carbon cycle, that covers the last millennium. The simulation is continued to the end of the twenty-first century. Besides state-of-the-art forcing reconstructions, we apply a modified reconstruction of total solar irradiance to shed light on the issue of forcing uncertainty in the context of the last millennium. Nevertheless, we find that structural uncertainties between different models can still dominate over forcing uncertainty for quantities such as hemispheric temperatures or the land and ocean carbon cycle response. Compared to other model simulations, we find forced decadal-scale variability to occur mainly after volcanic eruptions, while during other periods internal variability masks potentially forced signals and calls for larger ensembles in paleoclimate modeling studies. At the same time, we were not able to attribute millennial temperature trends to orbital forcing, as has been suggested recently. The climate–carbon-cycle sensitivity in CESM during the last millennium is estimated to be between 1.0 and 2.1 ppm °C−1. However, the dependence of this sensitivity on the exact time period and scale illustrates the prevailing challenge of deriving robust constraints on this quantity from paleoclimate proxies. In particular, the response of the land carbon cycle to volcanic forcing shows fundamental differences between different models. In CESM the tropical land dictates the response to volcanoes, with a distinct behavior for large and moderate eruptions. Under anthropogenic emissions, global land and ocean carbon uptake rates emerge from the envelope of interannual natural variability by about year 1947 and 1877, respectively, as simulated for the last millennium.

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Understanding drivers of glacier-length variability over the last millennium

The Cryosphere ◽

10.5194/tc-15-1645-2021 ◽

2021 ◽

Vol 15 (3) ◽

pp. 1645-1662

Author(s):

Alan Huston ◽

Nicholas Siler ◽

Gerard H. Roe ◽

Erin Pettit ◽

Nathan J. Steiger

Keyword(s):

Climate Variability ◽

Climate Model ◽

Volcanic Eruptions ◽

Internal Variability ◽

Forced Response ◽

Last Millennium ◽

External Forcing ◽

Climate History ◽

Temperature And Precipitation ◽

Glacier Length

Abstract. Changes in glacier length reflect the integrated response to local fluctuations in temperature and precipitation resulting from both external forcing (e.g., volcanic eruptions or anthropogenic CO2) and internal climate variability. In order to interpret the climate history reflected in the glacier moraine record, the influence of both sources of climate variability must therefore be considered. Here we study the last millennium of glacier-length variability across the globe using a simple dynamic glacier model, which we force with temperature and precipitation time series from a 13-member ensemble of simulations from a global climate model. The ensemble allows us to quantify the contributions to glacier-length variability from external forcing (given by the ensemble mean) and internal variability (given by the ensemble spread). Within this framework, we find that internal variability is the predominant source of length fluctuations for glaciers with a shorter response time (less than a few decades). However, for glaciers with longer response timescales (more than a few decades) external forcing has a greater influence than internal variability. We further find that external forcing also dominates when the response of glaciers from widely separated regions is averaged. Single-forcing simulations indicate that, for this climate model, most of the forced response over the last millennium, pre-anthropogenic warming, has been driven by global-scale temperature change associated with volcanic aerosols.

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Understanding Drivers of Glacier Length Variability Over the Last Millennium

10.5194/tc-2020-230 ◽

2020 ◽

Author(s):

Alan Huston ◽

Nicholas Siler ◽

Gerard H. Roe ◽

Erin Pettit ◽

Nathan J. Steiger

Keyword(s):

Climate Variability ◽

Volcanic Eruptions ◽

Internal Variability ◽

Forced Response ◽

Last Millennium ◽

External Forcing ◽

Climate History ◽

Temperature And Precipitation ◽

Glacier Length ◽

Length Changes

Abstract. Changes in glacier length reflect the integrated response to local fluctuations in temperature and precipitation resulting from both external forcing (e.g., volcanic eruptions or anthropogenic CO2) and internal climate variability. In order to interpret the climate history reflected in the glacier moraine record, therefore, the influence of both sources of climate variability must be considered. Here we study the last millennium of glacier length variability across the globe using a simple dynamic glacier model, which we force with temperature and precipitation time series from a 13-member ensemble of simulations from a global climate model. The ensemble allows us to quantify the contributions to glacier length variability from external forcing (given by the ensemble mean) and internal variability (given by the ensemble spread). Within this framework, we find that internal variability drives most length changes in mountain glaciers that have a response timescale of less than a few decades. However, for glaciers with longer response timescales (more than a few decades) external forcing has a greater influence than internal variability. We further find that external forcing also dominates when the response of glaciers from widely separated regions is averaged. Single-forcing simulations indicate that most of the forced response over the last millennium, pre-anthropogenic warming, has been driven by global-scale temperature change associated with volcanic aerosols.

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Climate and carbon cycle dynamics in a CESM simulation from 850–2100 CE

Earth System Dynamics Discussions ◽

10.5194/esdd-6-351-2015 ◽

2015 ◽

Vol 6 (1) ◽

pp. 351-406 ◽

Cited By ~ 3

Author(s):

F. Lehner ◽

F. Joos ◽

C. C. Raible ◽

J. Mignot ◽

A. Born ◽

...

Keyword(s):

Carbon Cycle ◽

Volcanic Eruptions ◽

Internal Variability ◽

Total Solar Irradiance ◽

Historical Period ◽

Last Millennium ◽

Coupled Modelling ◽

Decadal Scale ◽

Current Century ◽

Ocean Carbon

Abstract. Under the protocols of the Paleoclimate and Coupled Modelling Intercomparison Projects a number of simulations were produced that provide a range of potential climate evolutions from the last millennium to the end of the current century. Here, we present the first simulation with the Community Earth System Model (CESM), which includes an interactive carbon cycle, that continuously covers the last millennium, the historical period, and the twenty-first century. Besides state-of-the-art forcing reconstructions, we apply a modified reconstruction of total solar irradiance to shed light on the issue of forcing uncertainty in the context of the last millennium. Nevertheless, we find that structural uncertainties between different models can still dominate over forcing uncertainty for quantities such as hemispheric temperatures or the land and ocean carbon cycle response. Comparing with other model simulations we find forced decadal-scale variability to occur mainly after volcanic eruptions, while during other periods internal variability masks potentially forced signals and calls for larger ensembles in paleoclimate modeling studies. At the same time, we fail to attribute millennial temperature trends to orbital forcing, as has been suggested recently. The climate-carbon cycle sensitivity in CESM during the last millennium is estimated to be about 1.3 ppm °C−1. However, the dependence of this sensitivity on the exact time period and scale illustrates the prevailing challenge of deriving robust constrains on this quantity from paleoclimate proxies. In particular, the response of the land carbon cycle to volcanic forcing shows fundamental differences between different models. In CESM the tropical land dictates the response to volcanoes with a distinct behavior for large and moderate eruptions. Under anthropogenic emissions, global land and ocean carbon uptake rates emerge from the envelope of interannual natural variability as simulated for the last millennium by about year 1947 and 1877, respectively.

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Global hydroclimatic response to tropical volcanic eruptions over the last millennium

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2019145118 ◽

2021 ◽

Vol 118 (12) ◽

pp. e2019145118

Author(s):

Ernesto Tejedor ◽

Nathan J. Steiger ◽

Jason E. Smerdon ◽

Roberto Serrano-Notivoli ◽

Mathias Vuille

Keyword(s):

Volcanic Eruptions ◽

South American ◽

Last Millennium ◽

Temperature Changes ◽

The Past ◽

Model Response ◽

The Pacific ◽

Dry Conditions ◽

Community Earth System Model ◽

Past Millennium

Large tropical volcanic eruptions can affect the climate of many regions on Earth, yet it is uncertain how the largest eruptions over the past millennium may have altered Earth’s hydroclimate. Here, we analyze the global hydroclimatic response to all the tropical volcanic eruptions over the past millennium that were larger than the Mount Pinatubo eruption of 1991. Using the Paleo Hydrodynamics Data Assimilation product (PHYDA), we find that these large volcanic eruptions tended to produce dry conditions over tropical Africa, Central Asia and the Middle East and wet conditions over much of Oceania and the South American monsoon region. These anomalies are statistically significant, and they persisted for more than a decade in some regions. The persistence of the anomalies is associated with southward shifts in the Intertropical Convergence Zone and sea surface temperature changes in the Pacific and Atlantic oceans. We compare the PHYDA results with the stand-alone model response of the Community Earth System Model (CESM)-Last Millennium Ensemble. We find that the proxy-constrained PHYDA estimates are larger and more persistent than the responses simulated by CESM. Understanding which of these estimates is more realistic is critical for accurately characterizing the hydroclimate risks of future volcanic eruptions.

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Modeling of severe persistent droughts over eastern China during the last millennium

Climate of the Past ◽

10.5194/cp-10-1079-2014 ◽

2014 ◽

Vol 10 (3) ◽

pp. 1079-1091 ◽

Cited By ~ 18

Author(s):

Y. Peng ◽

C. Shen ◽

H. Cheng ◽

Y. Xu

Keyword(s):

Southern Oscillation ◽

Asian Summer Monsoon ◽

Eastern China ◽

Volcanic Eruptions ◽

Internal Variability ◽

Last Millennium ◽

Proxy Data ◽

Monsoon Variability ◽

Primary Driver ◽

Climate Forcings

Abstract. We use proxy data and modeled data from 1000 year model simulations with a variety of climate forcings to examine the occurrence of severe event of persistent drought over eastern China during the last millennium and diagnose the mechanisms. Results show that the model was able to roughly simulate most of these droughts over the study area during the last millennium such as those that occurred during the periods of 1123–1152, 1197–1223, 1353–1363, 1428–1449, 1479–1513, and 1632–1645. Our analyses suggest that these six well-captured droughts may caused by the East Asian summer monsoon (EASM) weakening. Study on the wavelet transform and spectral analysis reveals these events occurred all at the statistically significant 15–35-year timescale. A modeled data intercomparison suggests the possibility that solar activity may be the primary driver in the occurrence of the 1129–1144, 1354–1365, 1466–1491 and 1631–1648 droughts as identified by the model. However another possibility that these events may be related to internal variability cannot be excluded. Although the El Niño–Southern Oscillation (ENSO) plays an important role in monsoon variability, a temporally consistent relationship between the droughts and SST pattern in the Pacific Ocean could not be found either in the modeled or proxy data. Our analyses also indicate that large volcanic eruptions play a role as an amplifier in the drought of 1631–1648 and caused the droughts of 1830–1853 and 1958–1976, which was identified by the model.

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A multi-model analysis of ‘Little Ice Age’ climate over China

The Holocene ◽

10.1177/0959683618824761 ◽

2019 ◽

Vol 29 (4) ◽

pp. 592-605 ◽

Cited By ~ 2

Author(s):

Xuecheng Zhou ◽

Dabang Jiang ◽

Xianmei Lang

Keyword(s):

Little Ice Age ◽

Climate Models ◽

Surface Air Temperature ◽

Volcanic Eruptions ◽

Ice Age ◽

Last Millennium ◽

Orbital Parameters ◽

Community Earth System Model ◽

Intercomparison Project

Using the numerical experiments undertaken by nine climate models within the framework of the Paleoclimate Modeling Intercomparison Project Phase 3 (PMIP3), the ensemble simulations with the Community Earth System Model for the last millennium (CESM-LME), and proxy data, we investigate the climate over China during the ‘Little Ice Age’ (LIA; from 1450 to 1850 CE) against the background of the last millennium (from 850 to 1850 CE). The surface air temperature averaged over China generally decreased over time during the last millennium, with several multi-decadal to centennial variations superimposed on the long-term cooling. Relative to the climatology of the last millennium, the annual surface temperature during the LIA decreased over the country, with an average cooling of −0.07°C for the median of the PMIP3 models. Different magnitudes of cooling occurred in all seasons except spring. The cooling over China during the LIA was largely attributed to changes in volcanic eruptions and land use, while the change in orbital parameters played a role on a seasonal scale. The precipitation over China during the LIA decreased for the annual mean and summer and autumn but slightly increased in winter and spring. Model–data comparisons indicate that the models reproduced the colder and drier climate of the LIA reasonably, although there are some differences in certain aspects.

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Climate Variability and Change since 850 CE: An Ensemble Approach with the Community Earth System Model

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-14-00233.1 ◽

2016 ◽

Vol 97 (5) ◽

pp. 735-754 ◽

Cited By ~ 187

Author(s):

Bette L. Otto-Bliesner ◽

Esther C. Brady ◽

John Fasullo ◽

Alexandra Jahn ◽

Laura Landrum ◽

...

Keyword(s):

Climate Variability ◽

Ice Cores ◽

Volcanic Eruptions ◽

Internal Variability ◽

Earth System Model ◽

System Model ◽

Earth System ◽

The Past ◽

Community Earth System Model ◽

Past Millennium

Abstract The climate of the past millennium provides a baseline for understanding the background of natural climate variability upon which current anthropogenic changes are superimposed. As this period also contains high data density from proxy sources (e.g., ice cores, stalagmites, corals, tree rings, and sediments), it provides a unique opportunity for understanding both global and regional-scale climate responses to natural forcing. Toward that end, an ensemble of simulations with the Community Earth System Model (CESM) for the period 850–2005 (the CESM Last Millennium Ensemble, or CESM-LME) is now available to the community. This ensemble includes simulations forced with the transient evolution of solar intensity, volcanic emissions, greenhouse gases, aerosols, land-use conditions, and orbital parameters, both together and individually. The CESM-LME thus allows for evaluation of the relative contributions of external forcing and internal variability to changes evident in the paleoclimate data record, as well as providing a longer-term perspective for understanding events in the modern instrumental period. It also constitutes a dynamically consistent framework within which to diagnose mechanisms of regional variability. Results demonstrate an important influence of internal variability on regional responses of the climate system during the past millennium. All the forcings, particularly large volcanic eruptions, are found to be regionally influential during the preindustrial period, while anthropogenic greenhouse gas and aerosol changes dominate the forced variability of the mid- to late twentieth century.

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