Comparison of isotopic signatures in speleothem records and model simulations for the past millennium

2020 ◽  
Author(s):  
Janica Buehler ◽  
Moritz Kirschner ◽  
Carla Roesch ◽  
Max D. Holloway ◽  
Louise Sime ◽  
...  
Keyword(s):  
Climate Variability ◽  
Time Scales ◽  
General Circulation ◽  
General Circulation Models ◽  
Global Changes ◽  
Climate Change Scenarios ◽  
The Past ◽  
Proxy Records ◽  
Parameter Constraints ◽  
Past Millennium

<p>Global changes in climate, especially in mean temperature, receive increasing public as well as scientific attention under the current warming trend. However, the probability of extreme events and their societal impact is also governed by changes in climate variability. Improving the understanding of changes in both and their relationship is crucial for projecting reliable climate change scenarios. Model-data comparisons between general circulation models and speleothem paleoclimate archives, with δ<sup>18</sup>O as a temperature and precipitation proxy, have been suggested to test and validate the capability of different climate models.</p><p>Speleothems are precisely date-able and provide well preserved (semi-)continuous climate signals in the lower and mid-latitudes, providing a suitable archive to assess a model’s capability to simulate climate variability on time scales longer than those observable. However, the δ<sup>18</sup>O measured in speleothem calcite does not directly represent temperature or precipitation but results from multivariate, non-linear processes on top of the dominant meteoric controls on δ<sup>18</sup>O in precipitation.</p><p>Here, we evaluate correlations and networks between different records and power spectral densities across a speleothem database for the past millennium (850-2000CE), testing for representativity of individual records for the time period. Similarity measures are applied to proxy records and to the local climate variables obtained from three isotope-enabled HadCM3 simulations to evaluate simulation biases across different parameters and to distinguish main climate drivers for individual records or regions. The proxy records show strong damping of variability on shorter time scales compared to simulations down-sampled to record-resolution, acting like simple filter processes with realistic time scales for karst transit times.</p><p>Based on the evidence from proxies and models for the past 1000 years, we test for realistic parameter constraints and sufficient complexity of a speleothem proxy system model to represent low-latitude changes in climate variability on interannual to centennial timescales.</p>

Estimating Central Equatorial Pacific SST Variability over the Past Millennium. Part I: Methodology and Validation

2013 ◽  
Vol 26 (7) ◽  
pp. 2302-2328 ◽  
Author(s):  
Julien Emile-Geay ◽  
Kimberly M. Cobb ◽  
Michael E. Mann ◽  
Andrew T. Wittenberg
Keyword(s):  
General Circulation ◽  
Low Frequency ◽  
General Circulation Models ◽  
Performance Assessments ◽  
The Past ◽  
Proxy Records ◽  
Sst Variability ◽  
Predictive Skill ◽  
Climate Signals ◽  
Past Millennium

Abstract Constraining the low-frequency (LF) behavior of general circulation models (GCMs) requires reliable observational estimates of LF variability. This two-part paper presents multiproxy reconstructions of Niño-3.4 sea surface temperature over the last millennium, applying two techniques [composite plus scale (CPS) and hybrid regularized expectation maximization (RegEM) truncated total least squares (TTLS)] to a network of tropical, high-resolution proxy records. This first part presents the data and methodology before evaluating their predictive skill using frozen network analysis (FNA) and pseudoproxy experiments. The FNA results suggest that about half of the Niño-3.4 variance can be reconstructed back to A.D. 1000, but they show little LF skill during certain intervals. More variance can be reconstructed in the interannual band where climate signals are strongest, but this band is affected by dating uncertainties (which are not formally addressed here). The CPS reliably estimates interannual variability, while LF fluctuations are more faithfully reconstructed with RegEM, albeit with inevitable variance loss. The RegEM approach is also tested on representative pseudoproxy networks derived from two millennium-long integrations of a coupled GCM. The pseudoproxy study confirms that reconstruction skill is significant in both the interannual and LF bands, provided that sufficient variance is exhibited in the target Niño-3.4 index. It also suggests that FNA severely underestimates LF skill, even when LF variability is strong, resulting in overly pessimistic performance assessments. The centennial-scale variance of the historical Niño-3.4 index falls somewhere between the two model simulations, suggesting that the network and methodology presented here would be able to capture the leading LF variations in Niño-3.4 for much of the past millennium, with the caveats noted above.

scholarly journals Comparison of the oxygen isotope signatures in speleothem records and iHadCM3 model simulations for the last millennium

2020 ◽  
Author(s):  
Janica Carmen Bühler ◽  
Carla Roesch ◽  
Moritz Kirschner ◽  
Louise Sime ◽  
Max D Holloway ◽  
...  
Keyword(s):  
Climate Variability ◽  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Isotopic Ratio ◽  
Regional Climate ◽  
General Circulation Models ◽  
Global Changes ◽  
Last Millennium ◽  
Model Simulations

Abstract. Global changes in the climate, especially the warming trend in mean temperature, have received increasing public and scientific attention. Improving the understanding of changes in the mean and variability of climate variables as well as their interrelation is crucial for reliable climate change projections. Comparisons between general circulation models and paleoclimate archives using indirect proxies for temperature and/or precipitation have been used to test and validate the capability of climate models to represent climate changes. The oxygen isotopic ratio δ18O is routinely measured in speleothem samples at decadal or higher resolution and single specimens can cover full Glacial-Interglacial cycles. The calcium carbonate cave deposits are precisely dateable and provide well preserved (semi-) continuous, albeit multivariate climate signals in the lower and mid-latitudes, where the measured δ18O in the mineral does not directly represent temperature or precipitation. Therefore, speleothems represent suitable archives to assess simulated climate model abilities for the simulation of climate variability beyond the timescales covered by meteorological observations (10–100 yr). Here, we present three transient isotope enabled simulations from the Hadley Center Climate Model version 3 (iHadCM3) covering the last millennium (850–1850 CE) and compare these to a large global dataset of speleothem δ18O records from the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database version 2 (Comas-Bru et al., 2020). We evaluate systematically offsets in mean and variance of simulated δ18O and test for the main climate drivers for individual records or regions. The time-mean spatial offsets between the simulated δ18O and the speleothem data are fairly small. However, using robust filters and spectral analysis, we show that the observed proxy-based variability of δ18O is lower (higher) than simulated by iHadCM3 on decadal (centennial) timescales. Most of this difference can likely be attributed to the records' lower temporal resolution and averaging processes affecting the δ18O signal. Using cross-correlation analyses at site-level and modeled gridbox level, we find evidence for highly variable but generally low signal-to-noise ratios in the proxy data. This points at a high influence of cave-internal processes and regional climate particularities and could suggest low regional representativity of individual sites. Long-range strong positive correlations dominate the speleothem correlation network but are much weaker in the simulation. One reason for this could lie in a lack of longterm internal climate variability in these model simulations, which could be tested by repeating similar comparisons with other isotope-enabled climate models and paleoclimate databases.

scholarly journals Estimating Central Equatorial Pacific SST Variability over the Past Millennium. Part II: Reconstructions and Implications

2013 ◽  
Vol 26 (7) ◽  
pp. 2329-2352 ◽  
Author(s):  
Julien Emile-Geay ◽  
Kimberly M. Cobb ◽  
Michael E. Mann ◽  
Andrew T. Wittenberg
Keyword(s):  
Time Scales ◽  
Radiative Forcing ◽  
General Circulation ◽  
Tropical Pacific ◽  
Wavelet Coherence ◽  
The Past ◽  
Sst Variability ◽  
Wavelet Coherence Analysis ◽  
Past Millennium ◽  
The Tropical Pacific

Abstract Reducing the uncertainties surrounding the impacts of anthropogenic climate change requires vetting general circulation models (GCMs) against long records of past natural climate variability. This is particularly challenging in the tropical Pacific Ocean, where short, sparse instrumental data preclude GCM validation on multidecadal to centennial time scales. This two-part paper demonstrates the application of two statistical methodologies to a network of accurately dated tropical climate records to reconstruct sea surface temperature (SST) variability in the Niño-3.4 region over the past millennium. While Part I described the methods and established their validity and limitations, this paper presents several reconstructions of Niño-3.4, analyzes their sensitivity to procedural choices and input data, and compares them to climate forcing time series and previously published tropical Pacific SST reconstructions. The reconstructions herein show remarkably similar behavior at decadal to multidecadal scales, but diverge markedly on centennial scales. The amplitude of centennial variability in each reconstruction scales with the magnitude of the A.D. 1860–1995 trend in the target dataset’s Niño-3.4 index, with Extended Reconstructed SST, version 3 (ERSSTv3) > the Second Hadley Centre SST dataset (HadSST2) > Kaplan SST; these discrepancies constitute a major source of uncertainty in reconstructing preinstrumental Niño-3.4 SST. Despite inevitable variance losses, the reconstructed multidecadal variability exceeds that simulated by a state-of-the-art GCM (forced and unforced) over the past millennium, while reconstructed centennial variability is incompatible with constant boundary conditions. Wavelet coherence analysis reveals a robust antiphasing between solar forcing and Niño-3.4 SST on bicentennial time scales, but not on shorter time scales. Implications for GCM representations of the tropical Pacific climate response to radiative forcing are then discussed.

scholarly journals Comparison of spatial downscaling methods of general circulation models to study climate variability during the Last Glacial Maximum

2017 ◽  
Author(s):  
Guillaume Latombe ◽  
Ariane Burke ◽  
Mathieu Vrac ◽  
Guillaume Levavasseur ◽  
Christophe Dumas ◽  
...  
Keyword(s):  
Climate Variability ◽  
Last Glacial Maximum ◽  
General Circulation ◽  
General Circulation Models ◽  
Climate Conditions ◽  
The Past ◽  
Temperature And Precipitation ◽  
Paleoclimate Reconstructions ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The extent to which climate conditions influenced the spatial distribution of hominin populations in the past is highly debated. General Circulation Models (GCMs) and archaeological data have been used to address this issue. Most GCMs are not currently capable of simulating past surface climate conditions with sufficiently detailed spatial resolution to distinguish areas of potential hominin habitat, however. In this paper we propose a Statistical Downscaling Methods (SDM) for increasing the resolution of climate model outputs in a computationally efficient way. Our method uses a generalized additive model (GAM), calibrated over present-day data, to statistically downscale temperature and precipitation from the outputs of a GCM simulating the climate of the Last Glacial Maximum (19–23 000 BP) over Western Europe. Once the SDM is calibrated, we first interpolate the coarse-scale GCM outputs to the final resolution and then use the GAM to compute surface air temperature and precipitation levels using these interpolated GCM outputs and fine resolution geographical variables such as topography and distance from an ocean. The GAM acts as a transfer function, capturing non-linear relationships between variables at different spatial scales. We tested three different techniques for the first interpolation of GCM output: bilinear, bicubic, and kriging. The results were evaluated by comparing downscaled temperature and precipitation at local sites with paleoclimate reconstructions based on paleoclimate archives (archaeozoological and palynological data). Our results show that the simulated, downscaled temperature and precipitation values are in good agreement with paleoclimate reconstructions at local sites confirming that our method for producing fine-grained paleoclimate simulations suitable for conducting paleo-anthropological research is sound. In addition, the bilinear and bicubic interpolation techniques were shown to distort either the temporal variability or the values of the response variables, while the kriging method offers the best compromise. Since climate variability is an aspect of their environment to which human populations may have responded in the past this is an important distinction.

scholarly journals Dynamics of potential precipitation under climate change scenarios at Cameron highlands, Malaysia

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Nuraddeen Mukhtar Nasidi ◽  
Aimrun. Wayayok ◽  
Ahmad Fikri Abdullah ◽  
Muhamad Saufi Mohd Kassim
Keyword(s):  
Environmental Sustainability ◽  
General Circulation ◽  
Greenhouse Gas Emission ◽  
Rapid Change ◽  
Absolute Error ◽  
General Circulation Models ◽  
Coefficient Of Determination ◽  
Climate Change Scenarios ◽  
Precipitation Concentration Index ◽  
Cameron Highlands

AbstractPrecipitation is sensitive to increasing greenhouse gas emission which has a significant impact on environmental sustainability. Rapid change of climate variables is often result into large variation in rainfall characteristics which trigger other forms of hazards such as floods, erosion, and landslides. This study employed multi-model ensembled general circulation models (GCMs) approach to project precipitation into 2050s and 2080s periods under four RCPs emission scenarios. Spatial analysis was performed in ArcGIS10.5 environment using Inverse Distance Weighted (IDW) interpolation and Arc-Hydro extension. The model validation indicated by coefficient of determination, Nash–Sutcliffe efficiency, percent bias, root mean square error, standard error, and mean absolute error are 0.73, 0.27, 20.95, 1.25, 0.37 and 0.15, respectively. The results revealed that the Cameron Highlands will experience higher mean daily precipitations between 5.4 mm in 2050s and 9.6 mm in 2080s under RCP8.5 scenario, respectively. Analysis of precipitation concentration index (PCI) revealed that 75% of the watershed has PCI greater than 20 units which indicates substantial variability of the precipitation. Similarly, there is varied spatial distribution patterns of projected precipitation over the study watershed with the largest annual values ranged between 2900 and 3000 mm, covering 71% of the total area in 2080s under RCP8.5 scenario. Owing to this variability in rainfall magnitudes, appropriate measures for environmental protection are essential and to be strategized to address more vulnerable areas.

Solar-type periodicities in the climate variability of Northern Fennoscandia during the last three centuries: Real influence of solar activity or natural instability in the climate system

The Holocene ◽  
2021 ◽  
pp. 095968362110604
Author(s):  
Maxim Ogurtsov ◽  
Samuli Helama ◽  
Risto Jalkanen ◽  
Högne Jungner ◽  
Markus Lindholm ◽  
...  
Keyword(s):  
Solar Activity ◽  
Climate Variability ◽  
Western Siberia ◽  
Climate System ◽  
Solar Cycles ◽  
Activity Data ◽  
The Past ◽  
Proxy Records ◽  
Northern Fennoscandia ◽  
Solar Type

Fifteen proxy records of summer temperature in Fennoscandia, Northern Europe and in Yamal and Taymir Peninsulas (Western Siberia) were analyzed for the AD 1700–2000 period. Century-long (70–100 year) and quasi bi-decadal periodicities were found from proxy records representing different parts of Fennoscandia. Decadal variation was revealed in a smaller number of records. Statistically significant correlations were revealed between the timescale-dependent components of temperature variability and solar cycles of Schwabe (~11 year), Hale (~22 year), and Gleissberg (сentury-long) as recorded in solar activity data. Combining the results from our correlation analysis with the evidence of solar-climatic linkages over the Northern Fennoscandia obtained over the past 20 years suggest that there are two possible explanations for the obtained solar-proxy relations: (a) the Sun’s activity actually influences the climate variability in Northern Fennoscandia and in some regions of the Northern Hemisphere albeit the mechanism of such solar-climatic linkages are yet to be detailed; (b) the revealed solar-type periodicities result from natural instability of climate system and, in such a case, the correlations may appear purely by chance. Multiple lines of evidence support the first assumption but we note that the second one cannot be yet rejected. Guidelines for further research to elucidate this question are proposed including the Fisher’s combined probability test in the presence of solar signal in multiple proxy records.

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