Description: The stable hydrogen isotopes of C30-Alkanoic acids were measured from marine sediment core MD98-2152, collected off the southern coast of Sumatra, likely reflecting rainfall over southern Sumatra and western Java. The record extends to ~450,000 years before present and includes the five most recent glacial periods. To purify the leaf wax fatty acids for analysis, organic material was extracted from the sediment using an Accelerated Solvent Extractor, leaf waxes were isolated from each total lipid extract using column chromatography then methylated with methanol of a known isotopic composition to form fatty acid methyl esters, and purified with a final column. Hydrogen isotopes were measured using a gas chromatography-isotope ratio-monitoring mass spectrometer against Vienna Standard Mean Ocean Water (VSMOW). The hydrogen isotopes of the leaf wax fatty acids were then used in tandem with previously measured carbon isotopes of the same samples to calculate the hydrogen isotope values of precipitation, accounting for vegetation changes, through time following the methods in Tierney et al. (2017). This data was collected with the purpose of examining rainfall variability in the southern Indo-Pacific Warm Pool during glacial climates and to improve the spatial coverage of precipitation isotope records in the region. The age model and leaf wax carbon isotopes for MD98-2152 are available in Windler et al. (2019).

Description: A collection of geochemical SST proxy from the Last Glacial Maximum (23-19 ka) and the Late Holocene (4-0 ka) and results from data assimilation with iCESM 1.2. Includes raw proxy data from the LGM (Tierney2020_LGMProxyData.csv) and LH (Tierney2020_LHProxyData.csv) time slices, with calibrated absolute SSTs; "paired" (data in the same location) proxies with calibrated SST anomalies (Tierney2020_ProxyDataPaired.csv); a 5˚ x 5˚ gridded product of the paired proxies in netCDF format (Tierney2020_ProxyData_5x5_deltaSST.nc); and the results from the DA in netCDF format. The DA results are split into atmospheric variables (SAT, d18O of precipitation; Tierney2020_DA_atm.nc) and oceanic variables (SST, SSS, and d18O of seawater; Tierney2020_DA_ocn.nc). The ocean data are provided on their native tripolar grid (Tierney2020_DA_ocn.nc) as well as a 1 x 1 regridded version (Tierney2020_DA_ocn_regrid.nc).

Description: The Last Glacial Maximum (LGM, ∼ 21 000 years ago) has been a major focus for evaluating how well state-of-the-art climate models simulate climate changes as large as those expected in the future using paleoclimate reconstructions. A new generation of climate models has been used to generate LGM simulations as part of the Paleoclimate Modelling Intercomparison Project (PMIP) contribution to the Coupled Model Intercomparison Project (CMIP). Here, we provide a preliminary analysis and evaluation of the results of these LGM experiments (PMIP4, most of which are PMIP4-CMIP6) and compare them with the previous generation of simulations (PMIP3, most of which are PMIP3-CMIP5). We show that the global averages of the PMIP4 simulations span a larger range in terms of mean annual surface air temperature and mean annual precipitation compared to the PMIP3-CMIP5 simulations, with some PMIP4 simulations reaching a globally colder and drier state. However, the multi-model global cooling average is similar for the PMIP4 and PMIP3 ensembles, while the multi-model PMIP4 mean annual precipitation average is drier than the PMIP3 one. There are important differences in both atmospheric and oceanic circulations between the two sets of experiments, with the northern and southern jet streams being more poleward and the changes in the Atlantic Meridional Overturning Circulation being less pronounced in the PMIP4-CMIP6 simulations than in the PMIP3-CMIP5 simulations. Changes in simulated precipitation patterns are influenced by both temperature and circulation changes. Differences in simulated climate between individual models remain large. Therefore, although there are differences in the average behaviour across the two ensembles, the new simulation results are not fundamentally different from the PMIP3-CMIP5 results. Evaluation of large-scale climate features, such as land–sea contrast and polar amplification, confirms that the models capture these well and within the uncertainty of the paleoclimate reconstructions. Nevertheless, regional climate changes are less well simulated: the models underestimate extratropical cooling, particularly in winter, and precipitation changes. These results point to the utility of using paleoclimate simulations to understand the mechanisms of climate change and evaluate model performance.

Description: We present results from an ensemble of eight climate models, each of which has carried out simulations of the early Eocene climate optimum (EECO, ∼ 50 million years ago). These simulations have been carried out in the framework of the Deep-Time Model Intercomparison Project (DeepMIP; http://www.deepmip.org, last access: 10 January 2021); thus, all models have been configured with the same paleogeographic and vegetation boundary conditions. The results indicate that these non-CO2 boundary conditions contribute between 3 and 5 ∘C to Eocene warmth. Compared with results from previous studies, the DeepMIP simulations generally show a reduced spread of the global mean surface temperature response across the ensemble for a given atmospheric CO2 concentration as well as an increased climate sensitivity on average. An energy balance analysis of the model ensemble indicates that global mean warming in the Eocene compared with the preindustrial period mostly arises from decreases in emissivity due to the elevated CO2 concentration (and associated water vapour and long-wave cloud feedbacks), whereas the reduction in the Eocene in terms of the meridional temperature gradient is primarily due to emissivity and albedo changes owing to the non-CO2 boundary conditions (i.e. the removal of the Antarctic ice sheet and changes in vegetation). Three of the models (the Community Earth System Model, CESM; the Geophysical Fluid Dynamics Laboratory, GFDL, model; and the Norwegian Earth System Model, NorESM) show results that are consistent with the proxies in terms of the global mean temperature, meridional SST gradient, and CO2, without prescribing changes to model parameters. In addition, many of the models agree well with the first-order spatial patterns in the SST proxies. However, at a more regional scale, the models lack skill. In particular, the modelled anomalies are substantially lower than those indicated by the proxies in the southwest Pacific; here, modelled continental surface air temperature anomalies are more consistent with surface air temperature proxies, implying a possible inconsistency between marine and terrestrial temperatures in either the proxies or models in this region. Our aim is that the documentation of the large-scale features and model–data comparison presented herein will pave the way to further studies that explore aspects of the model simulations in more detail, for example the ocean circulation, hydrological cycle, and modes of variability, and encourage sensitivity studies to aspects such as paleogeography, orbital configuration, and aerosols.