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© Author(s) 2015. Artículo firmado por 24 autores. This work is distributed under the Creative Commons Attribution 3.0 License. This study is based on discussions held during the joint workshop of the PAGES 2k network and PAST2k-PMIP Integrated analyses of reconstructions and multimodel simulations for the past two millennia, Madrid, Spain, 4-6 November 2013. PAGES and FECYT (FCT-13-6276) are greatly thanked for supporting this workshop. We acknowledge the World Climate Research Programme's Working Group on Coupled Modelling, which is responsible for CMIP. The US Department of Energy's Program for Climate Model Diagnosis and Intercomparison provides coordinating support for CMIP and led the development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. H. Goosse is Research Director with the Fonds National de la Recherche Scientifique (F.R.S.-FNRS, Belgium). This work is supported by the F.R.S.-FNRS and by the Belgian Federal Science Policy Office (Research Programme on Science for a Sustainable Development). C. C. Raible and F. Lehner are supported by the Swiss National Science foundation. P. Yiou is supported by the MILEX project of the Swedish Research Council. J. Gergis is funded by Australian Research Council project DE130100668. O. Bothe was supported by LOCHMES (Leibniz Society), PRIME-II (within DFG INTERDYNAMIK), and CliSAP. L. Fernández Donado was funded by a FPU grant: AP2009-4061. A. Moberg and A. Hind are supported by the Swedish Research Council grants B0334901 and C0592401. G. Hegerl and A. Schurer are supported by the ERC advanced grant TITAN (320691). L. Fernández Donado, E. García Bustamente, and J. F. González Rouco were supported by grants CGL2011-29677-CO2-02 and CGL2014-59644-R. Gabi Hegerl was also supported by a Royal Society Wolfson Research Merit Award and by NCAS. This is LDEO contribution number 7956. N. McKay was funded through the US National Science Foundation (ARC-1107869)., Estimated external radiative forcings, model results, and proxy-based climate reconstructions have been used over the past several decades to improve our understanding of the mechanisms underlying observed climate variability and change over the past millennium. Here, the recent set of temperature reconstructions at the continental-scale generated by the PAGES 2k project and a collection of state-of-the-art model simulations driven by realistic external forcings are jointly analysed. The first aim is to estimate the consistency between model results and reconstructions for each continental-scale region over the time and frequency domains. Secondly, the links between regions are investigated to determine whether reconstructed global-scale covariability patterns are similar to those identified in model simulations. The third aim is to assess the role of external forcings in the observed temperature variations. From a large set of analyses, we conclude that models are in relatively good agreement with temperature reconstructions for Northern Hemisphere regions, particularly in the Arctic. This is likely due to the relatively large amplitude of the externally forced response across northern and high-latitude regions, which results in a clearly detectable signature in both reconstructions and simulations. Conversely, models disagree strongly with the reconstructions in the Southern Hemisphere. Furthermore, the simulations are more regionally coherent than the reconstructions, perhaps due to an underestimation of the magnitude of internal variability in models or to an overestimation of the response to the external forcing in the Southern Hemisphere. Part of the disagreement might also reflect large uncertainties in the reconstructions, specifically in some Southern Hemisphere regions, which are based on fewer palaeoclimate records than in the Northern Hemisphere., Unión Europea. FP7, Fonds de la Recherche Scientifique (F.R.S.-FNRS), Francia, Belgian Federal Science Policy Office (Research Programme on Science for a Sustainable Development), Swiss National Science foundation, MILEX project of the Swedish Research Council, Australian Research Council, LOCHMES (Leibniz Society), Precipitation in the past millennium in Europe (PRIME-II), Cluster of Excellence Integrated Climate System Analysis and Prediction (CliSAP), Formación del Profesorado Universitario (FPU) MECD, España, Swedish Research Council, Royal Society of London for Improving Natural Knowledge, National Centre for Atmospheric Science (NCAS), Reino Unido, US National Science Foundation, Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC), Deutsche Forschungsgemeinschaft (DFG), Alemania, Ministerio de Educación, Cultura y Deporte (MECD), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 License. This work was funded by the Spanish Ministry of the Environment (project SALVA-SINOVAS, Ref. 200800050083542) and the Spanish Ministry of Science and Technology (projects SPEQMORE-CGL2008-06558-C02-02/CLI and SPEQTRES-CGL2011-29672-C02-02). The authors also gratefully acknowledge funding from the Euro-Mediterranean Institute of Water (IEA). J. J. Gómez Navarro thanks the Spanish Ministry of Education for his Doctoral scholarship (AP2006-04100). The work by E. Zorita is embedded in the EU-Project Millennium European Climate. Thanks to Elena Bustamante for the stimulating discussions., In this study we analyse the role of internal variability in regional climate simulations through a comparison of two regional paleoclimate simulations for the last millennium. They share the same external forcings and model configuration, differing only in the initial condition used to run the driving global model simulation. A comparison of these simulations allows us to study the role of internal variability in climate models at regional scales, and how it affects the long-term evolution of climate variables such as temperature and precipitation. The results indicate that, although temperature is homogeneously sensitive to the effect of external forcings, the evolution of precipitation is more strongly governed by random unpredictable internal dynamics. There are, however, some areas where the role of internal variability is lower than expected, allowing precipitation to respond to the external forcings. In this respect, we explore the underlying physical mechanisms responsible for it. This study identifies areas, depending on the season, in which a direct comparison between model simulations of precipitation and climate reconstructions would be meaningful, but also other areas where good agreement between them should not be expected even if both are perfect., Ministerio de Agricultura, Alimentación y Medio Ambiente (MAGRAMA), España, Ministerio de Ciencia y Tecnología (MCYT), España, Euro-Mediterranean Institute of Water (IEA), Ministerio de Educación, Cultura y Deporte (MECD), España, Millennium project: European climate of the last millennium, Unión Europea (UE), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 License. This work is supported by the Sinergia project FUPSOL funded by the Swiss National Science Foundation. 20th Century Reanalysis data is provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA (from their website at http://www.esrl.noaa.gov/psd/). The CCSM3 simulations are performed on the super computing architecture of the Swiss National Supercomputing Centre (CSCS). LFD and JFGR were supported by CGL 2011-29677-602-02, CGL 2011-29672-602-01, and the FPU grant AP2009-4061., Atmospheric circulation modes are important concepts in understanding the variability of atmospheric dynamics. Assuming their spatial patterns to be fixed, such modes are often described by simple indices from rather short observational data sets. The increasing length of reanalysis products allows these concepts and assumptions to be scrutinised. Here we investigate the stability of spatial patterns of Northern Hemisphere teleconnections by using the Twentieth Century Reanalysis as well as several control and transient millennium-scale simulations with coupled models. The observed and simulated centre of action of the two major teleconnection patterns, the North Atlantic Oscillation (NAO) and to some extent the Pacific North American (PNA), are not stable in time. The currently observed dipole pattern of the NAO, its centre of action over Iceland and the Azores, split into a north-south dipole pattern in the western Atlantic with a wave train pattern in the eastern part, connecting the British Isles with West Greenland and the eastern Mediterranean during the period 1940-1969 AD. The PNA centres of action over Canada are shifted southwards and over Florida into the Gulf of Mexico during the period 1915-1944 AD. The analysis further shows that shifts in the centres of action of either teleconnection pattern are not related to changes in the external forcing applied in transient simulations of the last millennium. Such shifts in their centres of action are accompanied by changes in the relation of local precipitation and temperature with the overlying atmospheric mode. These findings further undermine the assumption of stationarity between local climate/proxy variability and large-scale dynamics inherent when using proxy-based reconstructions of atmospheric modes, and call for a more robust understanding of atmospheric variability on decadal timescales., project FUPSOL (Future and Past Solar Influence on the Terrestrial Climate), SNSF, Programa FPU (Formación de Profesorado Universitario), MECD, Swiss National Science Foundation (SNSF), Ministerio de Educación, Cultura y Deporte (MECD), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 License. We thank J.-C. Mareschal and the anonymous reviewer for their efforts, which improved this article considerably. VR was funded by the Ramón y Cajal Program (Gobierno de España, Ministerio de Educación, Cultura y Deporte), project CCG10-UCM/ESP-5070 (Comunidad de Madrid/UCM), and project CGL2011-29672-C02-01 (Gobierno de España, Ministerio de Economía y Competitividad)., The investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories. However, there are still many open questions concerning the significance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last Glacial Maximum is still present in borehole temperature profiles. It is shown here that this signal also influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries by producing errors in the determination of the steady state geothermal gradient. However, the impact on estimates of past temperature changes is weaker. For deeper boreholes, the curvature of the long-term signal is significant. A correction based on simple assumptions about glacial-interglacial temperature changes shows promising results, improving the extraction of millennial scale signals. The same procedure may help when comparing observed borehole temperature profiles with the results from numerical climate models., Programa Ramón y Cajal (MECD), Comunidad de Madrid, Ministerio de Economía y Competitividad (MINECO), España, Ministerio de Educación, Cultura y Deporte (MECD), España, Universidad Complutense de Madrid (UCM), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. This research was supported: in Spain by project SPECT (CGL2005-06097/CLI) and the Ramón y Cajal Program of the Ministerio de Educación y Ciencia (MEC) and project PalMA (CCG07-UCM/ESP-3045) by the Comunidad Autónoma de Madrid and the Universidad Complutense de Madrid; in Canada by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS) and the Atlantic Innovation Fund (AIF-ACOACanada); and in Germany by the EU project Millennium European Climate. The authors thank Vladimir Cermak and two anonymous reviewers for their comments and suggestions. Also we appreciate the contributions from Volker Rath and Jason Smerdon, editors of this special volume., Progress in understanding climate variability through the last millennium leans on simulation and reconstruction efforts. Exercises blending both approaches present a great potential for answering questions relevant both for the simulation and reconstruction of past climate, and depend on the specific peculiarities of proxies and methods involved in climate reconstructions, as well as on the realism and limitations of model simulations. This paper explores research specifically related to paleoclimate modeling and borehole climatology as a branch of climate reconstruction that has contributed significantly to our knowledge of the low frequency climate evolution during the last five centuries. The text flows around three main issues that group most of the interaction between model and geothermal efforts: the use of models as a validation tool for borehole climate reconstructions; comparison of geothermal information and model simulations as a means of either model validation or inference about past climate; and implications of the degree of realism on simulating subsurface climate on estimations of future climate change. The use of multi-centennial simulations as a surrogate reality for past climate suggests that within the simplified reality of climate models, methods and assumptions in borehole reconstructions deliver a consistent picture of past climate evolution at long time scales. Comparison of model simulations and borehole profiles indicate that borehole temperatures are responding to past external forcing and that more realism in the development of the soil model components in climate models is desirable. Such an improved degree of realism is important for the simulation of subsurface climate and air-ground interaction; results indicate it could also be crucial for simulating the adequate energy balance within climate change scenario experiments., SPECT, Programa Ramón y Cajal (Ministerio de Educación y Ciencia, MEC), Comunidad de Madrid, Universidad Complutense de Madrid (UCM), Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), Atlantic Innovation Fund (AIF-ACOACanada), Unión Europea (UE), Proyecto PalMA, Project Millennium European Climate (UE), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2013. LFD was funded by a FPU grant: AP2009-4061. LFD and JFGR acknowledge project grants UCM-921407, CGL2008-06558-C02-02/CLI, CGL2011-29672-C02-02, 200800050083542 and 200800050084028. CCR acknowledges SNF-FUPSOL. DB acknowledges projects CGL2008-05968-C02-01 and ENAC-PTDC/AAC-CLI/103567/2008. JL acknowledges EU/FP7-ACQWA-NO212250, DFG-PRIME1,2, LU1608/1-1/AOBJ:568460 and LU1608/2-1/AOBJ:575150. JS, DS and PY acknowledge the ANR ESCARSEL grant., Understanding natural climate variability and its driving factors is crucial to assessing future climate change. Therefore, comparing proxy-based climate reconstructions with forcing factors as well as comparing these with paleo-climate model simulations is key to gaining insights into the relative roles of internal versus forced variability. A review of the state of modelling of the climate of the last millennium prior to the CMIP5-PMIP3 (Coupled Model Intercomparison Project Phase 5-Paleoclimate Modelling Intercomparison Project Phase 3) coordinated effort is presented and compared to the available temperature reconstructions. Simulations and reconstructions broadly agree on reproducing the major temperature changes and suggest an overall linear response to external forcing on multidecadal or longer timescales. Internal variability is found to have an important influence at hemispheric and global scales. The spatial distribution of simulated temperature changes during the transition from the Medieval Climate Anomaly to the Little Ice Age disagrees with that found in the reconstructions. Thus, either internal variability is a possible major player in shaping temperature changes through the millennium or the model simulations have problems realistically representing the response pattern to external forcing. A last millennium transient climate response (LMTCR) is defined to provide a quantitative framework for analysing the consistency between simulated and reconstructed climate. Beyond an overall agreement between simulated and reconstructed LMTCR ranges, this analysis is able to single out specific discrepancies between some reconstructions and the ensemble of simulations. The disagreement is found in the cases where the reconstructions show reduced covariability with external forcings or when they present high rates of temperature change., FPU, SNF-FUPSOL, ANR ESCARSEL, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License. This work has been possible thanks to the funding by the MCINN projects CGL2005-06097 and CGL2008-06558-C02-C01/CLI, and the MARM project 200800050084028. The manuscript was significantly improved thanks to helpful and insightful comments of four anonymous reviewers. We are grateful to A. Grinsted and S. Jevrejeva for making the MatLab wavelet coherence package and their global sea level reconstructions available, and to A. Kemp for kindly sharing the data from North Carolina with us. We would also like to thank G. Sgubin for interesting discussions and to I. Fast for providing us with the extended FOR1 data.The publication of this article is financed by CNRS-INSU., Studies addressing climate variability during the last millennium generally focus on variables with a direct influence on climate variability, like the fast thermal response to varying radiative forcing, or the large-scale changes in atmospheric dynamics (e. g. North Atlantic Oscillation). The ocean responds to these variations by slowly integrating in depth the upper heat flux changes, thus producing a delayed influence on ocean heat content (OHC) that can later impact low frequency SST (sea surface temperature) variability through reemergence processes. In this study, both the externally and internally driven variations of the OHC during the last millennium are investigated using a set of fully coupled simulations with the ECHO-G (coupled climate model ECHAMA4 and ocean model HOPE-G) atmosphere-ocean general circulation model (AOGCM). When compared to observations for the last 55 yr, the model tends to overestimate the global trends and underestimate the decadal OHC variability. Extending the analysis back to the last one thousand years, the main impact of the radiative forcing is an OHC increase at high latitudes, explained to some extent by a reduction in cloud cover and the subsequent increase of short-wave radiation at the surface. This OHC response is dominated by the effect of volcanism in the preindustrial era, and by the fast increase of GHGs during the last 150 yr. Likewise, salient impacts from internal climate variability are observed at regional scales. For instance, upper temperature in the equatorial Pacific is controlled by ENSO (El Nino Southern Oscillation) variability from interannual to multidecadal timescales. Also, both the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) modulate intermittently the interdecadal OHC variability in the North Pacific and Mid Atlantic, respectively. The NAO, through its influence on North Atlantic surface heat fluxes and convection, also plays an important role on the OHC at multi, Ministerio de Ciencia e Innovación (MCINN), España, Ministerio de Medio Ambiente, Medio Rural y Marino (MARM), España, Centre national de la recherche scientifique CNRS-INSU, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License. This work was funded by the Spanish Ministry of the Environment (project SALVA-SINOVAS, Ref. 200800050083542) and the Spanish Ministry of Science and Technology (project SPECMORE-CGL2008-06558-C02-02/CLI). The authors also gratefully acknowledge the funding from the Euro-Mediterranean Institute of Water (IEA). We acknowledge the E-OBS data set from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (http://eca.knmi.nl). J. J. Gómez Navarro thanks the Spanish Ministry of Education for his Doctoral scholarship (AP2006-04100). We also thank Jürg Luterbacher for the interesting insights about uncertainties in proxy reconstructions, which improved the final version of this paper., A high-resolution (30 km) regional paleoclimate simulation of the last millennium over the Iberian Peninsula (IP) is presented. The simulation was performed with a climate version of the mesoscale model MM5 driven by the global model ECHO-G. Both models were driven by the same reconstructions of several external forcing factors. The high spatial resolution of the regional model allows climatologists to realistically simulate many aspects of the climate in the IP, as compared to an observational data set in the reference period 1961-1990. Although the spatial-averaged values developed by the regional model are tightly driven by the boundary conditions, it is capable to develop a different realisation of the past climate at regional scales, especially in the high-frequency domain and for precipitation. This has to be considered when comparing the results of climate simulations versus proxy reconstructions. A preliminary comparison of the simulation results with reconstructions of temperature and precipitation over the IP shows good agreement in the warming trends in the last century of the simulation, although there are large disagreements in key periods such as the precipitation anomalies in the Maunder Minimum., Ministerio de Medio Ambiente (MMA), Ministerio de Ciencia y Tecnología (MCYT), Euro-Mediterranean Institute of Water (IEA), Ministerio de Educación, Cultura y Deporte (MECD), ENSEMBLES-EU, Unión Europea. FP6, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2021. We are grateful for two anonymous reviewers and their thoughtful and constructive feedback. This analysis contributes to the PALEOLINK project (http://pastglobalchanges. org/science/wg/2knetwork/projects/paleolink/intro, last access: 16 February 2021), part of the PAGES 2k Network. Hugo Beltrami was supported by the Natural Sciences and Engineering Research Council of Canada, the Canada Research Chairs Program, and the Canada Foundation for Innovation. Hugo Beltrami holds the Canada Research Chair in Climate Dynamics. Almudena García-García and Francisco José Cuesta-Valero were funded by Hugo Beltrami’s Canada Research Chair program, the School of Graduate Students at the Memorial University of Newfoundland, and the Research Office at St. Francis Xavier University. This research has been supported by the Natural Sciences and Engineering Research Council of Canada (grant no. NSERC DG 140576948) and the Canada Research Chairs (grant no. CRC 230687)., Energy exchanges among climate subsystems are of critical importance to determine the climate sensitivity of the Earth’s system to greenhouse gases, to quantify the magnitude and evolution of the Earth’s energy imbalance, and to project the evolution of future climate. Thus, ascertaining the magnitude of and change in the Earth’s energy partition within climate subsystems has become urgent in recent years. Here, we provide new global estimates of changes in ground surface temperature, ground surface heat flux, and continental heat storage derived from geothermal data using an expanded database and new techniques. Results reveal markedly higher changes in ground heat flux and heat storage within the continental subsurface than previously reported, with land temperature changes of 1 K and continental heat gains of around 12 ZJ during the last part of the 20th century relative to preindustrial times. Half of the heat gain by the continental subsurface since 1960 has occurred in the last 20 years., Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs Program, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© Author(s) 2020. We gratefully acknowledge the IlModels (CGL2014-59644-R) and GreatModelS (RTI2018-102305-B-C21) projects. We also thank the CESM1(CAM5) Last Millennium Ensemble Community Project and supercomputing resources provided by the NSF, CISL and Yellowstone. This research has been supported by the Spanish Ministry of Economy, Industry and Competitiveness (grant no. BES-2015-075019)., Borehole-based reconstruction is a wellestablished technique to recover information of the past climate variability based on two main hypotheses: (1) past ground surface temperature (GST) histories can be recovered from borehole temperature profiles (BTPs); (2) the past GST evolution is coupled to surface air temperature (SAT) changes, and thus, past SAT changes can be recovered from BTPs. Compared to some of the last millennium (LM) proxy-based reconstructions, previous studies based on the borehole technique indicate a larger temperature increase during the last few centuries. The nature of these differences has fostered the assessment of this reconstruction technique in search of potential causes of bias. Here, we expand previous works to explore potential methodological and physical biases using pseudo-proxy experiments with the Community Earth System Model Last Millennium Ensemble (CESM-LME). A heat-conduction forward model driven by simulated surface temperature is used to generate synthetic BTPs that are then inverted using singular value decomposition. This procedure is applied to the set of simulations that incorporates all of the LM external forcing factors as well as those that consider the concentration of the green house gases (GHGs) and the land use land cover (LULC) changes forcings separately. The results indicate that methodological issues may impact the representation of the simulated GST at different spatial scales, with the temporal logging of the BTPs as the main sampling issue that may lead to an underestimation of the simulated GST 20th-century trends. Our analysis also shows that in the surrogate reality of the CESM-LME the GST does not fully capture the SAT warming during the industrial period, and thus, there may be a further underestimation of the past SAT changes due to physical processes. Globally, this effect is mainly influenced by the GHG forcing, whereas regionally, LULC changes and other forcings factors also contribute. These findi, Ministerio de Economía y Competitividad (MINECO), Fac. de Ciencias Físicas, TRUE, pub