scholarly journals The Paleoclimate reanalysis project

2015 ◽  
Vol 11 (5) ◽  
pp. 4159-4204 ◽  
Author(s):  
S. A. Browning ◽  
I. D. Goodwin
Keyword(s):  
Data Assimilation ◽  
World View ◽  
Internal Variability ◽  
Temporal Variations ◽  
Global Ocean ◽  
Model Data ◽  
Proxy Data ◽  
The Past ◽  
Spatial Fields ◽  
Past Millennium

Abstract. Recent advances in proxy-model data assimilation have made feasible the development of proxy-based reanalyses. Proxy-based reanalyses aim to make optimum use of both proxy and model data while presenting paleoclimate information in an accessible format – they will undoubtedly play a pivotal role in the future of paleoclimate research. In the Paleoclimate Reanalysis Project (PaleoR) we use "off-line" data assimilation to constrain the CESM1 (CAM5) Last Millennial Ensemble (LME) simulation with a globally distributed multivariate proxy dataset, producing a decadal resolution reanalysis of the past millennium. Discrete time periods are "reconstructed" by using anomalous (±0.5σ) proxy climate signals to select an ensemble of climate state analogues from the LME. Prior to assimilation the LME simulates internal variability that is temporally inconsistent with information from the proxy archive. After assimilation the LME is highly correlated to almost all included proxy data, and dynamical relationships between modelled variables are preserved; thus providing a "real-world" view of climate system evolution during the past millennium. Unlike traditional regression based approaches to paleoclimatology, PaleoR is unaffected by temporal variations in teleconnection patterns. Indices representing major modes of global ocean–atmosphere climate variability can be calculated directly from PaleoR spatial fields. PaleoR derived ENSO, SAM, and NAO indices are consistent with observations and published multiproxy reconstructions. The computational efficiency of "off-line" data assimilation allows easy incorporation and evaluation of new proxy data, and experimentation with different setups and model simulations. PaleoR spatial fields can be viewed online at http://climatefutures.mq.edu.au/research/themes/marine/paleor/.

scholarly journals Variability of summer precipitation over Eastern China during the last millennium

2009 ◽  
Vol 5 (2) ◽  
pp. 129-141 ◽  
Author(s):  
C. Shen ◽  
W.-C. Wang ◽  
Y. Peng ◽  
Y. Xu ◽  
J. Zheng
Keyword(s):  
Eastern China ◽  
Summer Precipitation ◽  
Internal Variability ◽  
Last Millennium ◽  
Model Data ◽  
Proxy Data ◽  
The Past ◽  
Temperature Regimes ◽  
Temporal And Spatial Variability ◽  
Temporal And Spatial

Abstract. We use measurements of recent decades, 1500-yr proxy data, and millennium model simulations with a variety of climate facings to study the temporal and spatial variability of summer precipitation over eastern China. Spectral analysis of the proxy data using multi-taper method reveals three statistically significant bidecadal (15–35-yr), pendadecadal (40–60-yr), and centennial (65–170-yr) oscillation bands. The results of wavelet filtering show that the amplitudes of these bands vary substantially through time depending on the temperature regimes. Weak centennial oscillation and strong pentadecadal oscillation occur in warm conditions, whereas both the centennial and pentadecadal oscillations are strong in cold conditions. A model/data intercomparison suggests that pentadecadal and bidecadal oscillations could be associated with internal variability of the climate system. It is also found that the increased frequency of drought-in-north/flood-in-south spatial pattern over eastern China during the last two decades is unusual in the past five centuries.

scholarly journals Variability of summer precipitation over eastern China during the last millennium

2008 ◽  
Vol 4 (3) ◽  
pp. 611-643 ◽  
Author(s):  
C. Shen ◽  
W.-C. Wang ◽  
Y. Peng ◽  
Y. Xu ◽  
J. Zheng
Keyword(s):  
Eastern China ◽  
Summer Precipitation ◽  
Internal Variability ◽  
Model Data ◽  
Solar Forcing ◽  
Proxy Data ◽  
The Past ◽  
Temperature Regimes ◽  
Temporal And Spatial Variability ◽  
Temporal And Spatial

Abstract. We use measurements of recent decades, 1500-yr proxy data, and millennium model simulations with a variety of climate facings to study the temporal and spatial variability of summer precipitation over eastern China. Spectral analysis of the proxy data using multi-taper method reveals three statistically significant bidecadal (15–35-yr), pendadecadal (40–60-yr), and centennial (65–170-yr) oscillation bands. The results of wavelet filtering show that the amplitudes of these bands vary substantially through time depending on the temperature regimes. Weak centennial oscillation and strong pentadecadal oscillation occur in warm conditions, whereas the oscillations are both strong in cold conditions. A model/data intercomparison suggests that the centennial oscillation might be linked to the fluctuation of solar forcing (Gleissberg cycle), and the pentadecadal and bidecadal oscillations could be associated with internal variability of the climate system. It is also found that the increased frequency of drought-in-north/flood-in-south spatial pattern over eastern China during the last two decades is unusual in the past five centuries.

scholarly journals The 15th century Arctic warming in coupled model simulations with data assimilation

2009 ◽  
Vol 5 (3) ◽  
pp. 389-401 ◽  
Author(s):  
E. Crespin ◽  
H. Goosse ◽  
T. Fichefet ◽  
M. E. Mann
Keyword(s):  
Data Assimilation ◽  
Surface Temperature ◽  
Climate Model ◽  
Three Dimensional ◽  
Coupled Model ◽  
Internal Variability ◽  
The Arctic ◽  
Arctic Warming ◽  
The Past ◽  
Past Millennium

Abstract. An ensemble of simulations of the climate of the past millennium conducted with a three-dimensional climate model of intermediate complexity are constrained to follow temperature histories obtained from a recent compilation of well-calibrated surface temperature proxies using a simple data assimilation technique. Those simulations provide a reconstruction of the climate of the Arctic that is compatible with the model physics, the forcing applied and the proxy records. Available observational data, proxy-based reconstructions and our model results suggest that the Arctic climate is characterized by substantial variations in surface temperature over the past millennium. Though the most recent decades are likely to be the warmest of the past millennium, we find evidence for substantial past warming episodes in the Arctic. In particular, our model reconstructions show a prominent warm event during the period 1470–1520. This warm period is likely related to the internal variability of the climate system, that is the variability present in the absence of any change in external forcing. We examine the roles of competing mechanisms that could potentially produce this anomaly. This study leads us to conclude that changes in atmospheric circulation, through enhanced southwesterly winds towards northern Europe, Siberia and Canada, are likely the main cause of the late 15th/early 16th century Arctic warming.

scholarly journals Potential causes of 15th century Arctic warming using coupled model simulations with data assimilation

2009 ◽  
Vol 5 (1) ◽  
pp. 1-27 ◽  
Author(s):  
E. Crespin ◽  
H. Goosse ◽  
T. Fichefet ◽  
M. E. Mann
Keyword(s):  
Data Assimilation ◽  
Surface Temperature ◽  
Climate Model ◽  
Coupled Model ◽  
Internal Variability ◽  
The Arctic ◽  
Arctic Warming ◽  
The Past ◽  
15Th Century ◽  
Past Millennium

Abstract. An ensemble of simulations of the climate of the past millennium using a three-dimensional climate model of intermediate complexity are constrained to follow temperature histories obtained from a recent compilation of well-calibrated surface temperature proxies using a simple data assimilation technique. Those simulations provide a reconstruction of the climate of the Arctic that is compatible with model physics, the forcing applied and the proxy records. Available observational data, proxy-based reconstructions and our model results suggest that the Arctic climate is characterized by substantial variations in surface temperature over the past millennium. Though the most recent decades are likely to be the warmest of the past millennium, we find evidence for substantial past warming episodes in the Arctic. In particular, our model reconstructions show a particularly warm period at the end of the 15th century. This warm event is likely related to the internal variability of the climate system. We examine the roles of competing mechanisms that could potentially produce this anomaly. These examinations lead us to conclude that changes in atmospheric circulation, through enhanced southwesterly winds towards northern Europe, Siberia and Canada, are likely the main cause of the Arctic warming during the late 15th century.

scholarly journals North Atlantic summer storm tracks over Europe dominated by internal variability over the past millennium

2016 ◽  
Vol 9 (8) ◽  
pp. 630-635 ◽  
Author(s):  
Mary H. Gagen ◽  
Eduardo Zorita ◽  
Danny McCarroll ◽  
Matthias Zahn ◽  
Giles H. F. Young ◽  
...  
Keyword(s):  
North Atlantic ◽  
Internal Variability ◽  
Storm Tracks ◽  
The Past ◽  
Summer Storm ◽  
Past Millennium

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

2016 ◽  
Vol 97 (5) ◽  
pp. 735-754 ◽  
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.

Using paleoclimate proxy-data to select optimal realisations in an ensemble of simulations of the climate of the past millennium

2006 ◽  
Vol 27 (2-3) ◽  
pp. 165-184 ◽  
Author(s):  
Hugues Goosse ◽  
Hans Renssen ◽  
Axel Timmermann ◽  
Raymond S. Bradley ◽  
Michael E. Mann
Keyword(s):  
Proxy Data ◽  
The Past ◽  
Paleoclimate Proxy ◽  
Past Millennium ◽  
Ensemble Of Simulations

scholarly journals Detecting an external influence on recent changes in oceanic oxygen using an optimal fingerprinting method

2013 ◽  
Vol 10 (3) ◽  
pp. 1799-1813 ◽  
Author(s):  
O. D. Andrews ◽  
N. L. Bindoff ◽  
P. R. Halloran ◽  
T. Ilyina ◽  
C. Le Quéré
Keyword(s):  
Internal Variability ◽  
Global Ocean ◽  
External Forcing ◽  
Dissolved Oxygen Concentration ◽  
The Past ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Optimal Fingerprinting ◽  
Earth System Models ◽  
Ocean Deoxygenation

Abstract. Ocean deoxygenation has been observed in all major ocean basins over the past 50 yr. Although this signal is largely consistent with oxygen changes expected from anthropogenic climate change, the contribution of external forcing to recent deoxygenation trends relative to natural internal variability is yet to be established. Here we conduct a formal optimal fingerprinting analysis to investigate if external forcing has had a detectable influence on observed dissolved oxygen concentration ([O2]) changes between ∼1970 and ∼1992 using simulations from two Earth System Models (MPI-ESM-LR and HadGEM2-ES). We detect a response to external forcing at a 90% confidence level and find that observed [O2] changes are inconsistent with internal variability as simulated by models. This result is robust in the global ocean for depth-averaged (1-D) zonal mean patterns of [O2] change in both models. Further analysis with the MPI-ESM-LR model shows similar positive detection results for depth-resolved (2-D) zonal mean [O2] changes globally and for the Pacific Ocean individually. Observed oxygen changes in the Atlantic Ocean are indistinguishable from natural internal variability. Simulations from both models consistently underestimate the amplitude of historical [O2] changes in response to external forcing, suggesting that model projections for future ocean deoxygenation may also be underestimated.

scholarly journals Detecting an external influence on recent changes in oceanic oxygen using an optimal fingerprinting method

2012 ◽  
Vol 9 (9) ◽  
pp. 12469-12504 ◽  
Author(s):  
O. D. Andrews ◽  
N. L. Bindoff ◽  
P. R. Halloran ◽  
T. Ilyina ◽  
C. Le Quéré
Keyword(s):  
Internal Variability ◽  
Global Ocean ◽  
External Forcing ◽  
Dissolved Oxygen Concentration ◽  
The Past ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Optimal Fingerprinting ◽  
Earth System Models ◽  
Ocean Deoxygenation

Abstract. Ocean deoxygenation has been observed in all major ocean basins over the past 50 yr. Although this signal is largely consistent with oxygen changes expected from anthropogenic climate change, the contribution of external forcing to recent deoxygenation trends relative to natural internal variability is yet to be established. Here we conduct a formal optimal fingerprinting analysis to investigate if external forcing has had a detectable influence on observed dissolved oxygen concentration ([O2]) changes between ~ 1970 and ~ 1992 using simulations from two Earth System Models (MPI-ESM-LR and HadGEM2-ES). We detect a response to external forcing at a 90% confidence level and find that observed [O2] changes are inconsistent with internal variability as simulated by models. This result is robust in the global ocean for depth-averaged (1-D) zonal mean patterns of [O2] change in both models. Further analysis with the MPI-ESM-LR model shows similar positive detection results for depth-resolved (2-D) zonal mean [O2] changes globally and for the Pacific Ocean individually. Observed oxygen changes in the Atlantic Ocean are indistinguishable from natural internal variability. Simulations from both models consistently underestimate the amplitude of historical [O2] changes in response to external forcing, suggesting that model projections for future ocean deoxygenation may also be underestimated.

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