Olivia Truax

Proxy time series suggest that Holocene summer warmth peaked asynchronously across Greenland, but the extent to which these differences reflect coherent regional climate patterns remains unclear. We compile 38 quantitative and qualitative summer-temperature proxy time series from Greenland and adjacent seas and apply an uncertainty-weighted factor analysis framework that accommodates heterogeneous proxy types to identify coherent temporal and spatial patterns from 10 ka to present. We compare these proxy-derived factors with those for five proxy-informed paleoclimate reconstructions and a transient model-only baseline. Two factors best represent the proxy network. The leading temporal mode reaches a maximum by 7.2 ka, reflecting early-to-mid Holocene warmth in northern and eastern Greenland, and contrasts with delayed warming in western Greenland. We interpret this pattern as an insolation-driven summer-temperature response modified by meltwater, ocean stratification, and sea-ice dynamics during retreat of the Laurentide and Greenland ice sheets. The second temporal mode peaks by 5.4 ka and is strongest in southern and southwestern Greenland, which may reflect an increased coastal influence of Atlantic-origin heat transported by the Irminger and West Greenland currents. Climate reconstructions reproduce the temporal evolution of the proxy-derived factors more successfully than their spatial patterns. Two paleoclimate reconstructions provide the closest agreement, but no existing reconstruction reproduces the complete regional structure of the proxy network. Despite proxy and chronological uncertainties, this analysis demonstrates that heterogeneous proxies can resolve coherent spatiotemporal patterns in Holocene Greenland climate, providing a basis for mechanistic interpretation and an empirical benchmark for evaluating paleoclimate reconstructions.

Antarctic ice cores provide highly detailed climate histories; yet, the existing proxy record is limited by uneven spatial and temporal coverage. Collecting new ice cores will improve our understanding of climate processes in Antarctica, but the cost of drilling new records demands careful site selection. Here, we present a data-driven optimal sensor approach to select ice core sites that best constrain a chosen climate metric by iteratively applying an Ensemble Kalman Filter. We demonstrate the method by choosing two Antarctic-wide metrics: average annually resolved temperature and annual accumulation since the Industrial Era. Our approach accounts for proxy uncertainty based on the site accumulation rate; we discuss logistical constraints for specific case studies. We find that the southern Ross Ice Shelf and western Dronning Maud Land are optimal regions to reconstruct Antarctic-wide total accumulation and average temperature, respectively. We describe three case studies: 1) drilling a new core at Crary Ice Rise on the Ross Ice Shelf; 2) drilling a new core at Lyddan Ice Rise in Dronning Maud Land; and 3) redrilling the US-ITASE cores in West Antarctica. Our data-driven methodology can guide future community drilling efforts to maximize the value of new ice cores for climate reconstruction.

The Greenland Ice Sheet (GrIS) is a major contributor to sea-level rise, yet its long-term response to sustained warmth remains uncertain ^1,2,3 . The Holocene represents the most recent interval during which the GrIS experienced centuries of temperatures above preindustrial levels, providing a natural benchmark for assessing its sensitivity to prolonged warming ^4,5 . However, reproducing the geologically constrained evolution of the GrIS throughout the Holocene has remained a persistent challenge for ice-sheet models ^6,7 . Here we present GrIS simulations forced by paleoclimate reconstructions and evaluated against extensive geological constraints to reconstruct its evolution from the Holocene to 2300 CE. By simultaneously capturing multiple independent records of past ice-sheet change, our ensemble provides a robust foundation for future projections. Under current warming trajectories, the GrIS shrinks below its Holocene minimum extent and volume by 2300 CE, while mass loss rates exceed Holocene maxima and contribute 26–86 cm of sea-level equivalent. Continued warming drives a nonlinear expansion of the ablation zone beyond its Holocene range, whereas substantial emissions reductions limit the sea-level contribution to approximately 10 cm. These results indicate that future warming may push the Greenland Ice Sheet beyond the range of states experienced during the Holocene.

Climate variability over the last two millennia (Past2k) reflects the combined influence of internal climate dynamics, including modes such as ENSO, external forcings such as volcanic and solar activity, and, in recent centuries, increasing anthropogenic forcing. Studying the Past2k period provides critical context for understanding current and future climate change in a warming world. In the pre-instrumental era, the absence of direct climate observations necessitated reliance on climate models and paleoclimate archives to infer past climate conditions.Paleoclimate data assimilation (PDA) is an effective approach to integrate the information from both climate models and natural proxies. Here, we employ an offline PDA framework to generate a new spatiotemporally resolved global reconstruction of the Past2k at annual and seasonal (summer and winter) resolution, including key climate fields (e.g., temperature, pressure, precipitation), drought indices (scPDSI, SPEI), and climate indices (e.g., ENSO, PDO, AO).Proxy observations are compiled from the Iso2k, PAGES2k, CoralHydro2k, and SISALv3 databases, together with additional tree-ring width datasets. The model priors are derived from isotope-enabled Earth system model simulations using MPI-ESM-wiso and iCESM.Relative to previous global reconstructions, this assimilation framework advances PDA by explicitly assimilating isotopic proxy records, employing physically based proxy system models, accounting for proxy seasonality and climate sensitivity, and incorporating low-resolution records across multiple timescales. We conducted comprehensive evaluations of the reconstructed fields and indices against instrumental/reanalysis datasets, as well as existing global PDA-based reconstructions, and also assessed the reconstruction skill in earlier centuries. These evaluations show that our reconstructions perform well and yield reliable results. We expect that our datasets will provide a millennial-scale climate context to support further studies of past climate variability and to inform analyses of ongoing and future climate change.

The Ross Ice Shelf buttresses ice draining from both East and West Antarctica and its collapse could accelerate the loss of inland ice sheets, rapidly raising sea level. Documenting the location, timing and rate of past glacial retreat can help reveal processes driving rapid mass loss, informing projections of ice sheet responses to a warming climate. Here, we present a record of mid-Holocene ice retreat from the southwestern Ross Sea using facies succession and paired ramped pyrolysis oxidation ¹⁴ C/ ²¹⁰ Pb chronology. This record shows rapid ice shelf retreat from 6.9-5.4 cal kyr BP, coeval with thinning of adjacent outlet glaciers. Our findings reconcile earlier discrepancies in terrestrial and marine reconstructions, and indicate that synchronous grounding line retreat from west of Ross Island to the Siple Coast at ~7-6.2 cal kyr BP was likely driven by warm-water incursions, a process active in parts of Antarctica today.

We present a mid‐to‐late Holocene record of relative paleosecular variation from the Ross Sea region of Antarctica. The 6,700‐year‐long record of inclination, declination, and relative paleointensity from a marine sediment core collected near Cape Adare is independently dated using a combination of ramped pyrolysis oxidation and carbonate radiocarbon dates. Agreement between the large‐scale features of the relative paleointensity record and the virtual axial geomagnetic dipole moment suggests that changes in the record are dominated by the dipole component of the Earth's geomagnetic field. Correspondence between the record and a non‐independently dated reconstruction from the Antarctic Peninsula indicates regionally coherent changes in the geomagnetic field intensity in the southern high latitudes during the mid‐to‐late Holocene. The prominent features of the record serve as stratigraphic markers for hard‐to‐date Antarctic sedimentary records and a constraint on Holocene geomagnetic field behavior when incorporated into the next generation of geomagnetic field models.

Aotearoa New Zealand prides itself on achieving remarkable outcomes with limited resources and embraces a national identity rooted in innovation, resilience, and efficiency. But even number-8 wire can snap. As newly appointed academics navigating the country's research landscape, we have encountered a funding system stretched beyond its limits - one that threatens the integrity and sustainability of the research it is meant to support. Here, we argue that a central issue in the current system is Aotearoa's heavy reliance on indirect cost recovery - or "overheads" - to fund core institutional functions. We explore how this internationally anomalous system undermines research excellence by incentivizing budget-driven project design, fragmenting researchers' time, obstructing career development for early career researchers, and destabilizing institutional budgets through volatile, grant-dependent income. At a time when colleagues in Public Research Organizations - formerly Crown Research Institutes - face job insecurity and uncertainty, we feel obligated to speak out, in line with our role as the "critic and conscience of society" (Education and Training Act, 2022). As the nation restructures its public research system, we argue that core institutional funding must be decoupled from competitive research grants, which should be dedicated to supporting the direct costs of research.

The Royal Society Te Apārangi Early Career Researcher (ECR) forum represents researchers in Aotearoa New Zealand across various research sectors encompassing Crown Research Institutes (CRIs), Industry Training Organisations (ITOs), and universities to better support ECR career development. Despite recommendations to integrate these research sectors, the system is still segmented with rising numbers of PhD graduates, limited post-doctoral opportunities, and challenges associated with a changing research system. Recent efforts, including funding reforms and new fellowship schemes, aim to address these issues but remain insufficient. This paper highlights ongoing disparities and the need for a framework that fosters ECR mobility and professional growth. It calls for strategic reforms in training and funding systems, supporting integrated pathways, equitable opportunities, and fostering of ECRs across diverse research environments.

Increasing snow accumulation over the Antarctic Ice Sheet may mitigate future sea level rise. However, current estimates of mitigation potential are poorly constrained due to limited records of past variability. We present an annually resolved reconstruction of Antarctic snow accumulation from 1801 to 2000 CE, employing a paleoclimate data assimilation methodology to integrate ice core records with a multi‐model ensemble of climate simulations. Our reconstruction correlates well with instrumental reanalysis, and we find that Antarctic accumulation rates increased over the 20th‐century, resulting in a modest amount (∼1 mm) of sea level mitigation. Mitigation is primarily driven by an accelerating trend since around 1970. Our results contrast with previous mitigation estimates of ∼10–12 mm; this discrepancy is due to poorly constrained baseline estimates of 19th‐century accumulation in East Antarctica. Our reconstruction suggests that the uncertainty of future sea level mitigation from increasing Antarctic accumulation has been underestimated.