scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 3: Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing

2015 ◽  
Vol 11 (3) ◽  
pp. 425-448 ◽  
Author(s):  
A. Moberg ◽  
R. Sundberg ◽  
H. Grudd ◽  
A. Hind
Keyword(s):  
Tree Ring ◽  
Large Amplitude ◽  
Small Amplitude ◽  
Climate Model ◽  
Last Millennium ◽  
Solar Forcing ◽  
Proxy Data ◽  
Statistical Framework ◽  
Tree Ring Data ◽  
Climate Model Simulations

Abstract. A statistical framework for evaluation of climate model simulations by comparison with climate observations from instrumental and proxy data (part 1 in this series) is improved by the relaxation of two assumptions. This allows autocorrelation in the statistical model for simulated internal climate variability and enables direct comparison of two alternative forced simulations to test whether one fits the observations significantly better than the other. The extended framework is applied to a set of simulations driven with forcings for the pre-industrial period 1000–1849 CE and 15 tree-ring-based temperature proxy series. Simulations run with only one external forcing (land use, volcanic, small-amplitude solar, or large-amplitude solar) do not significantly capture the variability in the tree-ring data – although the simulation with volcanic forcing does so for some experiment settings. When all forcings are combined (using either the small- or large-amplitude solar forcing), including also orbital, greenhouse-gas and non-volcanic aerosol forcing, and additionally used to produce small simulation ensembles starting from slightly different initial ocean conditions, the resulting simulations are highly capable of capturing some observed variability. Nevertheless, for some choices in the experiment design, they are not significantly closer to the observations than when unforced simulations are used, due to highly variable results between regions. It is also not possible to tell whether the small-amplitude or large-amplitude solar forcing causes the multiple-forcing simulations to be closer to the reconstructed temperature variability. Proxy data from more regions and of more types, or representing larger regions and complementary seasons, are apparently needed for more conclusive results from model–data comparisons in the last millennium.

scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 3: Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing

2014 ◽  
Vol 10 (3) ◽  
pp. 2627-2683
Author(s):  
A. Moberg ◽  
R. Sundberg ◽  
H. Grudd ◽  
A. Hind
Keyword(s):  
Tree Ring ◽  
Large Amplitude ◽  
Small Amplitude ◽  
Climate Model ◽  
Last Millennium ◽  
Solar Forcing ◽  
Proxy Data ◽  
Statistical Framework ◽  
Tree Ring Data ◽  
Climate Model Simulations

Abstract. Practical issues arise when applying a statistical framework for unbiased ranking of alternative forced climate model simulations by comparison with climate observations from instrumental and proxy data (Part 1 in this series). Given a set of model and observational data, several decisions need to be made; e.g. concerning the region that each proxy series represents, the weighting of different regions, and the time resolution to use in the analysis. Objective selection criteria cannot be made here, but we argue to study how sensitive the results are to the choices made. The framework is improved by the relaxation of two assumptions; to allow autocorrelation in the statistical model for simulated climate variability, and to enable direct comparison of alternative simulations to test if any of them fit the observations significantly better. The extended framework is applied to a set of simulations driven with forcings for the pre-industrial period 1000–1849 CE and fifteen tree-ring based temperature proxy series. Simulations run with only one external forcing (land-use, volcanic, small-amplitude solar, or large-amplitude solar), do not significantly capture the variability in the tree-ring data – although the simulation with volcanic forcing does so for some experiment settings. When all forcings are combined (using either the small- or large-amplitude solar forcing) including also orbital, greenhouse-gas and non-volcanic aerosol forcing, and additionally used to produce small simulation ensembles starting from slightly different initial ocean conditions, the resulting simulations are highly capable of capturing some observed variability. Nevertheless, for some choices in the experiment design, they are not significantly closer to the observations than when unforced simulations are used, due to highly variable results between regions. It is also not possible to tell whether the small-amplitude or large-amplitude solar forcing causes the multiple-forcing simulations to be closer to the reconstructed temperature variability. This suggests that proxy data from more regions and proxy types, or representing larger regions and other seasons, are needed for more conclusive results from model-data comparisons in the last millennium.

scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium

2012 ◽  
Vol 8 (1) ◽  
pp. 263-320 ◽  
Author(s):  
A. Hind ◽  
A. Moberg ◽  
R. Sundberg
Keyword(s):  
Climate Model ◽  
Distance Measure ◽  
Last Millennium ◽  
Proxy Data ◽  
Simulation Data ◽  
Model Simulations ◽  
Climate Proxy ◽  
Statistical Framework ◽  
Climate Model Simulations ◽  
Instrumental Series

Abstract. A statistical framework for comparing the output of ensemble simulations from global climate models with networks of climate proxy and instrumental records is developed, focusing on near-surface temperatures for the last millennium. This framework includes the formulation of a joint statistical model for proxy data, instrumental data and simulation data, which is used to optimize a quadratic distance measure for ranking climate model simulations. An essential underlying assumption is that the simulations and the proxy/instrumental series have a shared component of variability that is due to temporal changes in external forcing, such as volcanic aerosol load, solar irradiance changes and greenhouse gas concentrations. Two statistical tests are formulated. Firstly, a preliminary test to establish whether a significant temporal correlation exists between instrumental/proxy and simulation data. Secondly, the distance measure is expressed in the form of a test statistic of whether a forced simulation is closer to the instrumental/proxy series than unforced simulations. The proposed framework allows any number of proxy locations to be used jointly, with different seasons, record lengths and statistical precision. The new methods are applied in a pseudo-proxy experiment. Here, a set of previously published millennial forced model simulations, including both "low" and "high" solar radiative forcing histories together with other common forcings, were used to define "true" target temperatures as well as pseudo-proxy and pseudo-instrumental series. The pseudo-proxies were created to reflect current proxy locations and noise levels, where it was found that the low and high solar full-forcing simulations could be distinguished when the latter were used as targets. When the former were used as targets, a greater number of proxy locations were needed to make this distinction. It was also found that to improve detectability of the low solar simulations, increasing the signal-to-noise ratio was more efficient than increasing the spatial coverage of the proxy network. In the next phase of the work, we will apply these methods to real proxy and instrumental data, with the aim to distinguish which of the two solar forcing histories is most compatible with the observed/reconstructed climate.

scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 1: Theory

2012 ◽  
Vol 8 (4) ◽  
pp. 1339-1353 ◽  
Author(s):  
R. Sundberg ◽  
A. Moberg ◽  
A. Hind
Keyword(s):  
Climate Model ◽  
Distance Measure ◽  
Last Millennium ◽  
Proxy Data ◽  
Simulation Data ◽  
Model Simulations ◽  
Climate Proxy ◽  
Statistical Framework ◽  
Climate Model Simulations ◽  
Instrumental Records

Abstract. A statistical framework for comparing the output of ensemble simulations from global climate models with networks of climate proxy and instrumental records has been developed, focusing on near-surface temperatures for the last millennium. This framework includes the formulation of a joint statistical model for proxy data, instrumental data and simulation data, which is used to optimize a quadratic distance measure for ranking climate model simulations. An essential underlying assumption is that the simulations and the proxy/instrumental series have a shared component of variability that is due to temporal changes in external forcing, such as volcanic aerosol load, solar irradiance or greenhouse gas concentrations. Two statistical tests have been formulated. Firstly, a preliminary test establishes whether a significant temporal correlation exists between instrumental/proxy and simulation data. Secondly, the distance measure is expressed in the form of a test statistic of whether a forced simulation is closer to the instrumental/proxy series than unforced simulations. The proposed framework allows any number of proxy locations to be used jointly, with different seasons, record lengths and statistical precision. The goal is to objectively rank several competing climate model simulations (e.g. with alternative model parameterizations or alternative forcing histories) by means of their goodness of fit to the unobservable true past climate variations, as estimated from noisy proxy data and instrumental observations.

Resolving the differences in the simulated and reconstructed climate response to volcanism over the last millennium

2020 ◽  
Author(s):  
Feng Zhu ◽  
Julien Emile-Geay ◽  
Greg Hakim ◽  
Jonathan King ◽  
Kevin Anchukaitis
Keyword(s):  
Tree Ring ◽  
Radiative Forcing ◽  
Natural Experiment ◽  
Climate Model ◽  
Simulated Data ◽  
Growing Season ◽  
Explosive Volcanism ◽  
Last Millennium ◽  
Climate Response ◽  
Climate Model Simulations

<p>Explosive volcanism imposes impulse-like radiative forcing on the climate system, providing a natural experiment to study the climate response to perturbation. Previous studies have identified disagreements between paleoclimate reconstructions and climate model simulations (GCMs) with respect to the magnitude and recovery from volcanic cooling, questioning the fidelity of GCMs, reconstructions, or both. Using the paleoenvironmental data assimilation framework of the Last Millennium Reanalysis, this study investigates the causes of the disagreements, using both real and simulated data. We demonstrate that the disagreement may be resolved by assimilating tree-ring density records only, by targeting growing-season temperature instead of annual temperature, and by performing the comparison at proxy locales. Our work suggests that discrepancies between paleoclimate models and data can be largely resolved by accounting for these features of tree-ring proxy networks.</p>

scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 2: A pseudo-proxy study addressing the amplitude of solar forcing

2012 ◽  
Vol 8 (4) ◽  
pp. 1355-1365 ◽  
Author(s):  
A. Hind ◽  
A. Moberg ◽  
R. Sundberg
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Signal To Noise Ratio ◽  
Noise Levels ◽  
Solar Forcing ◽  
Max Planck ◽  
Statistical Framework ◽  
Spatial Coverage ◽  
Climate Model Simulations ◽  
Instrumental Records

Abstract. The statistical framework of Part 1 (Sundberg et al., 2012), for comparing ensemble simulation surface temperature output with temperature proxy and instrumental records, is implemented in a pseudo-proxy experiment. A set of previously published millennial forced simulations (Max Planck Institute – COSMOS), including both "low" and "high" solar radiative forcing histories together with other important forcings, was used to define "true" target temperatures as well as pseudo-proxy and pseudo-instrumental series. In a global land-only experiment, using annual mean temperatures at a 30-yr time resolution with realistic proxy noise levels, it was found that the low and high solar full-forcing simulations could be distinguished. In an additional experiment, where pseudo-proxies were created to reflect a current set of proxy locations and noise levels, the low and high solar forcing simulations could only be distinguished when the latter served as targets. To improve detectability of the low solar simulations, increasing the signal-to-noise ratio in local temperature proxies was more efficient than increasing the spatial coverage of the proxy network. The experiences gained here will be of guidance when these methods are applied to real proxy and instrumental data, for example when the aim is to distinguish which of the alternative solar forcing histories is most compatible with the observed/reconstructed climate.

scholarly journals Teleconnections and relationship between the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) in reconstructions and models over the past millennium

2020 ◽  
Vol 16 (2) ◽  
pp. 743-756 ◽  
Author(s):  
Christoph Dätwyler ◽  
Martin Grosjean ◽  
Nathan J. Steiger ◽  
Raphael Neukom
Keyword(s):  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Last Millennium ◽  
Annular Mode ◽  
Model Simulations ◽  
The Past ◽  
Climate Model Simulations ◽  
Past Millennium

Abstract. The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Because of the limited length of instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability over time. Using proxy-based reconstructions and last-millennium climate model simulations, we find that ENSO and SAM indices are mostly negatively correlated over the past millennium. Pseudo-proxy experiments indicate that currently available proxy records are able to reliably capture ENSO–SAM relationships back to at least 1600 CE. Palaeoclimate reconstructions show mostly negative correlations back to about 1400 CE. An ensemble of last-millennium climate model simulations confirms this negative correlation, showing a stable correlation of approximately −0.3. Despite this generally negative relationship we do find intermittent periods of positive ENSO–SAM correlations in individual model simulations and in the palaeoclimate reconstructions. We do not find evidence that these relationship fluctuations are caused by exogenous forcing nor by a consistent climate pattern. However, we do find evidence that strong negative correlations are associated with strong positive (negative) anomalies in the Interdecadal Pacific Oscillation and the Amundsen Sea Low during periods when SAM and ENSO indices are of opposite (equal) sign.

scholarly journals The DeepMIP contribution to PMIP4: methodologies for selection, compilation and analysis of latest Paleocene and early Eocene climate proxy data, incorporating version 0.1 of the DeepMIP database

2019 ◽  
Vol 12 (7) ◽  
pp. 3149-3206 ◽  
Author(s):  
Christopher J. Hollis ◽  
Tom Dunkley Jones ◽  
Eleni Anagnostou ◽  
Peter K. Bijl ◽  
Margot J. Cramwinckel ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Early Eocene ◽  
Proxy Data ◽  
Time Model ◽  
Deep Time ◽  
Climate Proxy ◽  
Early Eocene Climatic Optimum ◽  
Climate Model Simulations ◽  
Atmospheric Co2 Concentrations

Abstract. The early Eocene (56 to 48 million years ago) is inferred to have been the most recent time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Global mean temperatures were also substantially warmer than those of the present day. As such, the study of early Eocene climate provides insight into how a super-warm Earth system behaves and offers an opportunity to evaluate climate models under conditions of high greenhouse gas forcing. The Deep Time Model Intercomparison Project (DeepMIP) is a systematic model–model and model–data intercomparison of three early Paleogene time slices: latest Paleocene, Paleocene–Eocene thermal maximum (PETM) and early Eocene climatic optimum (EECO). A previous article outlined the model experimental design for climate model simulations. In this article, we outline the methodologies to be used for the compilation and analysis of climate proxy data, primarily proxies for temperature and CO2. This paper establishes the protocols for a concerted and coordinated effort to compile the climate proxy records across a wide geographic range. The resulting climate “atlas” will be used to constrain and evaluate climate models for the three selected time intervals and provide insights into the mechanisms that control these warm climate states. We provide version 0.1 of this database, in anticipation that this will be expanded in subsequent publications.

Impact of the 536/540 CE double volcanic eruption event on the 6th-7th century climate using model and proxy data

2020 ◽  
Author(s):  
Evelien van Dijk ◽  
Claudia Timmreck ◽  
Johann Jungclaus ◽  
Stephan Lorenz ◽  
Manon Bajard ◽  
...  
Keyword(s):  
Tree Ring ◽  
Volcanic Eruption ◽  
Detailed Comparison ◽  
Arctic Sea Ice ◽  
Special Focus ◽  
Decadal Climate Variability ◽  
Proxy Data ◽  
Tree Ring Data ◽  
Volcanic Forcing ◽  
The Impact

<p>The mid of the 6<sup>th</sup> century is an outstanding period and started with an unusual cold period that lasted several years to decades, due to the 536/540 CE double eruption event, with the strongest decadal volcanic forcing in the last 2000 years. Evidence from multiple tree ring records from the Alps to the Altai Mountains in Russia identified a centennial cooling lasting from 536 up to 660 CE. A previous Earth System Model (ESM) study with reconstructed volcanic forcing covering 535-550 CE like conditions already found that the double eruption led to a global decrease in temperature and an increase in Arctic sea-ice for at least a decade. However, the simulations were too short to fully investigate the multi-decadal cooling event and the atmospheric forcing from this double volcanic eruption alone may not be enough to sustain such a prolonged cooling. To better understand forced versus internal decadal climate variability in the first millennium we have performed mid 6<sup>th</sup> century ensemble simulations with the MPI-ESM1.2 for the 520-680 CE period. The ensemble consists of 10 realizations, which were branched of the MPI-ESM1.2 PMIP4 Past2k run, including the evolv2k volcanic forcing.</p><p>Here, we present results of this new set of the 6<sup>th</sup>-7<sup>th</sup> century MPI-ESM simulations in comparison to paleo-proxies. Summer surface temperatures are analyzed and compared with available tree-ring data, which fits very well for the entire 160 year period. As part of the VIKINGS project, special focus is placed on the impact of the 536/540 CE double volcanic eruption event on the surface climate in the Northern Hemisphere, in particular Scandinavia, Northern Europe and Siberia. The goal is to also compare the model data with new tree-ring and lake sediment proxies from southeastern Norway. Detailed comparison with proxy data will allow us to better understand the regional and seasonal climate variations of the 6<sup>th</sup>-7<sup>th</sup> century. Duration, strength and the possible mechanism for a long lasting volcanic induced cooling will be discussed.</p>

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