TY  - JOUR
A1  - Reschke, Maria
A1  - Rehfeld, Kira
A1  - Laepple, Thomas
T1  - Empirical estimate of the signal content of Holocene temperature proxy records
JF  - Climate of the past : an interactive open access journal of the European Geosciences Union
N2  - Proxy records from climate archives provide evidence about past climate changes, but the recorded signal is affected by non-climate-related effects as well as time uncertainty. As proxy-based climate reconstructions are frequently used to test climate models and to quantitatively infer past climate, we need to improve our understanding of the proxy record signal content as well as the uncertainties involved. In this study, we empirically estimate signal-to-noise ratios (SNRs) of temperature proxy records used in global compilations of the middle to late Holocene (last 6000 years). This is achieved through a comparison of the correlation of proxy time series from nearby sites of three compilations and model time series extracted at the proxy sites from two transient climate model simulations: a Holocene simulation of the ECHAM5/MPI-OM model and the Holocene part of the TraCE-21ka simulation. In all comparisons, we found the mean correlations of the proxy time series on centennial to millennial timescales to be low (R < 0.2), even for nearby sites, which resulted in low SNR estimates. The estimated SNRs depend on the assumed time uncertainty of the proxy records, the timescale analysed, and the model simulation used. Using the spatial correlation structure of the ECHAM5/MPI-OM simulation, the estimated SNRs on centennial timescales ranged from 0.05 - assuming no time uncertainty - to 0.5 for a time uncertainty of 400 years. On millennial timescales, the estimated SNRs were generally higher. Use of the TraCE-21ka correlation structure generally resulted in lower SNR estimates than for ECHAM5/MPI-OM. As the number of available high-resolution proxy records continues to grow, a more detailed analysis of the signal content of specific proxy types should become feasible in the near future. The estimated low signal content of Holocene temperature compilations should caution against over-interpretation of these multi-proxy and multisite syntheses until further studies are able to facilitate a better characterisation of the signal content in paleoclimate records.
Y1  - 2019
U6  - https://doi.org/10.5194/cp-15-521-2019
SN  - 1814-9324
SN  - 1814-9332
VL  - 15
IS  - 2
SP  - 521
EP  - 537
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Comas-Bru, Laia
A1  - Harrison, Sandy P.
A1  - Werner, Martin
A1  - Rehfeld, Kira
A1  - Scroxton, Nick
A1  - Veiga-Pires, Cristina
A1  - Ahmad, Syed Masood
A1  - Brahim, Yassine Ait
A1  - Mozhdehi, Sahar Amirnezhad
A1  - Arienzo, Monica
A1  - Atsawawaranunt, Kamolphat
A1  - Baker, Andy
A1  - Braun, Kerstin
A1  - Breitenbach, Sebastian Franz Martin
A1  - Burstyn, Yuval
A1  - Chawchai, Sakonvan
A1  - Columbu, Andrea
A1  - Deininger, Michael
A1  - Demeny, Attila
A1  - Dixon, Bronwyn
A1  - Hatvani, Istvan Gabor
A1  - Hu, Jun
A1  - Kaushal, Nikita
A1  - Kern, Zoltan
A1  - Labuhn, Inga
A1  - Lachniet, Matthew S.
A1  - Lechleitner, Franziska A.
A1  - Lorrey, Andrew
A1  - Markowska, Monika
A1  - Nehme, Carole
A1  - Novello, Valdir F.
A1  - Oster, Jessica
A1  - Perez-Mejias, Carlos
A1  - Pickering, Robyn
A1  - Sekhon, Natasha
A1  - Wang, Xianfeng
A1  - Warken, Sophie
A1  - Atkinson, Tim
A1  - Ayalon, Avner
A1  - Baldini, James
A1  - Bar-Matthews, Miryam
A1  - Bernal, Juan Pablo
A1  - Boch, Ronny
A1  - Borsato, Andrea
A1  - Boyd, Meighan
A1  - Brierley, Chris
A1  - Cai, Yanjun
A1  - Carolin, Stacy
A1  - Cheng, Hai
A1  - Constantin, Silviu
A1  - Couchoud, Isabelle
A1  - Cruz, Francisco
A1  - Denniston, Rhawn
A1  - Dragusin, Virgil
A1  - Duan, Wuhui
A1  - Ersek, Vasile
A1  - Finne, Martin
A1  - Fleitmann, Dominik
A1  - Fohlmeister, Jens Bernd
A1  - Frappier, Amy
A1  - Genty, Dominique
A1  - Holzkamper, Steffen
A1  - Hopley, Philip
A1  - Johnston, Vanessa
A1  - Kathayat, Gayatri
A1  - Keenan-Jones, Duncan
A1  - Koltai, Gabriella
A1  - Li, Ting-Yong
A1  - Lone, Mahjoor Ahmad
A1  - Luetscher, Marc
A1  - Mattey, Dave
A1  - Moreno, Ana
A1  - Moseley, Gina
A1  - Psomiadis, David
A1  - Ruan, Jiaoyang
A1  - Scholz, Denis
A1  - Sha, Lijuan
A1  - Smith, Andrew Christopher
A1  - Strikis, Nicolas
A1  - Treble, Pauline
A1  - Unal-Imer, Ezgi
A1  - Vaks, Anton
A1  - Vansteenberge, Stef
A1  - Voarintsoa, Ny Riavo G.
A1  - Wong, Corinne
A1  - Wortham, Barbara
A1  - Wurtzel, Jennifer
A1  - Zhang, Haiwei
T1  - Evaluating model outputs using integrated global speleothem records of climate change since the last glacial
JF  - Climate of the past : an interactive open access journal of the European Geosciences Union
N2  - Although quantitative isotope data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to using the speleothem data for data–model comparisons. Here, we illustrate this using 456 globally distributed speleothem δ18O records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates the process of procuring large numbers of records if data–model comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. To circumvent this issue, we illustrate techniques through which the absolute isotope values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model's ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotope data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on δ18O values, the optimum period for the modern observational baseline and the selection of an appropriate time window for creating means of the isotope data for palaeo-time-slices.
Y1  - 2019
U6  - https://doi.org/10.5194/cp-15-1557-2019
SN  - 1814-9324
SN  - 1814-9332
VL  - 15
IS  - 4
SP  - 1557
EP  - 1579
PB  - Copernicus
CY  - Göttingen
ER  -