This paper hypothesizes that the Meteor Crater impact in Arizona, USA, 56,000 years ago triggered landslides in Grand Canyon that dammed the Colorado River and formed Nankoweap paleolake. This is compatible with shock and earthquake physics for the impact that infer a M5.4 seismic event, attenuated to an effective magnitude of M3.5 at Grand Canyon. Results that support the hypothesis include radiocarbon dating of driftwood and luminescence dating of associated slack-water lake sediments that are preserved in caves up to 60 m above the modern Colorado River. Radiocarbon ages from two locations, including Stanton’s Cave, date the driftwood as 55.25 ± 2.44 ka (n = 4). Sediments associated with the driftwood gave a luminescence age of 56.00 ± 6.39 ka (n = 2). These six Grand Canyon dates, and three published ages for the Meteor Crater impact, show statistically indistinguishable results that support the hypothesis for a geologically instantaneous series of events with a mean age of 55.60 ± 1.30 ka. This work highlights the value of radiocarbon dating near the limits of the technique, integration of multiple dating methods, and seismic and landslide hazards associated with meteorite impacts in regions of extreme topography like Grand Canyon.

Extratropical peatlands in the Southern Hemisphere preserve detailed information on climatic and environmental change going back millennia. They are particularly valuable for understanding the evolution of the mid-latitude southern westerly winds (SWW), which play a major role in driving regional temperature and precipitation patterns, Antarctic sea-ice extent and ocean carbon fluxes. Here we investigate the timing and drivers of peatland initiation across the southern mid-latitudes after the Last Glacial Maximum (21,000 years ago) and test how this might relate to past changes in the SWW. We radiocarbon-date basal peats from the Falkland Islands and collate published basal peat radiocarbon ages from peat-forming regions south of 35° S. Using kernel density estimate models, we find distinct latitudinal phases of post-glacial peat initiation that suggest that peat growth is sensitive to variations in SWW position through their influence on moisture availability, temperature and dust deposition. A peak in peat growth in regions north of 52.5° S during the Antarctic Cold Reversal (14,700–12,800 years ago) suggests an equatorward migration of the SWW, coinciding with a slowdown in atmospheric CO2 increases. In light of recent SWW intensification and poleward migration, our findings highlight the potential for ongoing changes in the Southern Hemisphere climate and carbon fluxes under continued anthropogenic heating. Coherent patterns in the initial growth of extratropical peatlands throughout the Southern Hemisphere during the last glacial track changes in the latitudinal position of the southern westerly winds, according to an analysis of basal peat radiocarbon ages.

The development of reliable sediment chronologies is crucial for accurate interpretations of decadal to century-scale palaeoenvironmental changes in the late Quaternary. Although radiocarbon dating of sedimentary sequences is commonly undertaken, not all the organic fractions are representative of atmospheric C-14 levels, resulting in inaccurate age models. Whilst terrestrial plant macrofossils are widely considered ideal dating material - assuming they are contemporaneous with the horizons being dated - they are often sparse or absent. In this context, radiocarbon dating of pollen extracts is increasingly being used as alternative dating material. Here, we used pollen radiocarbon dating, alongside a suite of macrofossil and bulk sediment dates, to develop a chronology for the Holocene sediments of Lake Surprise, in Victoria, Australia. Pb-210 activity and Plutonium (Pu) concentrations and isotope ratios were also analysed to constrain the age of the uppermost sediments, augmented with recent historical markers, including the first arrival of Pinus pollen and the date of an earlier coring expedition at the site in 2004. With respect to the radiocarbon dates, we found an age offset between the plant macrofossils and bulk sediment dates of 260 +/- 86 C-14 years and an offset of similar to 340 C-14 years between plant macrofossil and pollen extracts. In both cases, macrofossil dates appeared to be "younger" than the bulk sediment and pollen dates. The offset between pollen and plant macrofossil dates was found to vary with sediment depth and generally correlate with carbonate concentration in the sediment. Using Fourier transform infrared spectroscopy (FTIR), we determined that the pollen extracts were not contaminated by either carbonate or charcoal. However, contamination by algal spores could not be ruled out, and we hypothesise that those algal spores may have assimilated aged dissolved inorganic carbon during periods of higher groundwater influx, thus altering the measured radiocarbon age of the pollen extract. Macrofossil and corrected pollen radiocarbon dates were incorporated in a Bayesian age-depth model which integrated Pb-210 activities and Pu data and bomb pulse C-14 dates validated using recent historical age markers. Our results suggest that it is possible to generate a robust geochronological framework for Lake Surprise using radiocarbon dating back to at least similar to 10,846 cal yr BP.

Solar particle events (SPEs) are short-lived bursts of high-energy particles from the solar atmosphere and are widely recognized as posing significant economic risks to modern society. Most SPEs are relatively weak and have minor impacts on the Earth's environment, but historic records contain much stronger SPEs which have the potential to alter atmospheric chemistry, impacting climate and biological life. The impacts of such strong SPEs would be far more severe when the Earth's protective geomagnetic field is weak, such as during past geomagnetic excursions or reversals. Here, we model the impacts of an extreme SPE under different geomagnetic field strengths, focusing on changes in atmospheric chemistry and surface radiation using the atmosphere-ocean-chemistry-climate model SOCOL3-MPIOM and the radiation transfer model LibRadtran. Under current geomagnetic conditions, an extreme SPE would increase NOx concentrations in the polar stratosphere and mesosphere, causing reductions in extratropical stratospheric ozone lasting for about a year. In contrast, with no geomagnetic field, there would be a substantial increase in NOx throughout the entire atmosphere, resulting in severe stratospheric ozone depletion for several years. The resulting ground-level ultraviolet (UV) radiation would remain elevated for up to 6 y, leading to increases in UV index up to 20 to 25% and solar-induced DNA damage rates by 40 to 50%. The potential evolutionary impacts of past extreme SPEs remain an important question, while the risks they pose to human health in modern conditions continue to be underestimated.

Prehistoric Polynesian voyaging into high latitudes with landfall in Antarctica remains a widely credited proposition. We examine it through archaeological and environmental evidence from the Subantarctic region of the southwest Pacific, focussing upon an extensive archaeological site at Sandy Bay on Enderby Island. Combining a new set of radiocarbon ages with former, older, ages we show that the site is now within the same rapid expansion phase in which South Polynesia was first colonised. Radiocarbon ages across the site indicate a single continuous settlement, probably of some decades. Consideration of limiting factors in Subantarctic settlement, including of seafaring capability and critical resources, suggests that the site was about as far south as prehistoric habitation could be sustained and was probably vacated at the onset of the Little Ice age (LIA) in the late 14th century. An absence of prehistoric remains on islands further south also suggests that Polynesian exploration reached a boundary 2000 km short of Antarctica. The southern case is discussed briefly in the wider context of Polynesian expansion. Les voyages polyn & eacute;siens pr & eacute;historiques vers les hautes latitudes avec atterrissage en Antarctique restent une proposition largement reconnue. Nous l'examinons & agrave; travers des preuves arch & eacute;ologiques et environnementales provenant de la r & eacute;gion subantarctique du sud-ouest du Pacifique, en nous concentrant sur un vaste site arch & eacute;ologique & agrave; Sandy Bay sur l'& icirc;le Enderby. En combinant un nouvel ensemble d'& acirc;ges au radiocarbone avec des & acirc;ges ant & eacute;rieurs, plus anciens, nous montrons que le site se trouve d & eacute;sormais dans la m & ecirc;me phase d'expansion rapide dans laquelle la Polyn & eacute;sie du Sud a & eacute;t & eacute; colonis & eacute;e pour la premi & egrave;re fois. Les & acirc;ges au radiocarbone sur l'ensemble du site indiquent un seul & eacute;tablissement continu, probablement de plusieurs d & eacute;cennies. La prise en compte des facteurs limitants du peuplement subantarctique, notamment la capacit & eacute; de navigation et les ressources critiques, sugg & egrave;re que le site se trouvait & agrave; peu pr & egrave;s aussi au sud que l'habitation pr & eacute;historique pouvait & ecirc;tre soutenue et qu'il a probablement & eacute;t & eacute; lib & eacute;r & eacute; au d & eacute;but du Petit Acirc;ge Glaciaire (LIA) & agrave; la fin du XIVe si & egrave;cle. L'absence de vestiges pr & eacute;historiques sur les & icirc;les plus au sud sugg & egrave;re & eacute;galement que l'exploration polyn & eacute;sienne a atteint une fronti & egrave;re situ & eacute;e & agrave; 2 000 km de l'Antarctique. Le cas m & eacute;ridional est bri & egrave;vement discut & eacute; dans le contexte plus large de l'expansion polyn & eacute;sienne.

Recent extremes of flood and drought across Australia have raised questions about the recurrence of such rare events and highlighted the importance of understanding multi-decadal climate variability. However, instrumental records over the past century are too short to adequately characterise climate variability on multi-decadal and longer timescales or robustly determine extreme event frequencies and their duration. Palaeoclimate reconstructions can provide much-needed information to help address this problem. Here, we use the 600-year hydroclimate record captured in the eastern Australian and New Zealand Drought Atlas (ANZDA) to analyse drought and pluvial frequency trends for East Australian Natural Resource Management (NRM) clusters. This partitioning of the drought atlas grid points into recognised biophysical areas (i.e. NRM clusters) revealed their differences and similarities in drought intensity and pluvial events over time. We find sustained multi-decadal periods of a wet–dry geographic 'seesaw' between eastern to central and southern NRMs (e.g. 1550–1600 CE and 1700–1750 CE). In contrast, other periods reveal spatially consistent wetting (e.g. 1500–1550 CE) or drying (e.g. 1750–1800 CE). Emerging hot spot analysis further shows that some areas that appear naturally buffered from severe drought during the instrumental period have a greater exposure risk when the longer 600-year record is considered. These findings are particularly relevant to management plans when dealing with the impacts of climate extremes developed at regional scales. Our results demonstrate that integrating and extending instrumental records with palaeoclimate datasets will become increasingly important for developing robust and locally specific extreme event frequency information for managing water resources.

We report the discovery of an ancient forest bed near Stanley, on the Falkland Islands, the second such ancient deposit identified on the South Atlantic island archipelago that is today marked by the absence of native tree species. Fossil pollen, spores and wood fragments preserved in this buried deposit at Tussac House show that the source vegetation was characterized by a floristically diverse rainforest dominated by Nothofagus -Podocarpaceae communities, similar to cool temperate Nothofagus forests/woodlands and Magellanic evergreen Nothofagus rainforests. The age limit of the deposit is inferred from the stratigraphic distribution of fossil pollen species transported by wind, birds or ocean currents from southern Patagonia, as well as similar vegetation types observed across the broader region. The deposit is suggested to be between Late Oligocene and Early Miocene, making it slightly older than the previously analysed Neogene West Point Island forest bed (200 km west of Tussac House ). The combined evidence adds to our current knowledge of the role of climate change and transoceanic dispersal of plant propagules in shaping high-latitude ecosystems in the Southern Hemisphere during the late Palaeogene and Neogene.

Radiocarbon (14C) is essential for creating chronologies to study the timings and drivers of pivotal events in human history and the Earth system over the past 55,000 years. It is also a fundamental proxy for investigating solar processes, including the potential of the Sun for extreme activity. Until now, fluctuations in past atmospheric 14C levels have limited the dating precision possible using radiocarbon. However, the discovery of solar super-storms known as extreme solar particle events (ESPEs) has driven a series of advances with the potential to transform the calendar-age precision of radiocarbon dating. Organic materials containing unique 14C ESPE signatures can now be dated to annual precision. In parallel, the search for further storms using high-precision annual 14C measurements has revealed fine-scaled variations that can be used to improve calendar-age precision, even in periods that lack ESPEs. Furthermore, the newly identified 14C fluctuations provide unprecedented insight into solar variability and the carbon cycle. Here, we review the current state of knowledge and share our insights into these rapidly developing, diverse research fields. We identify links between radiocarbon, archaeology, solar physics and Earth science to stimulate transdisciplinary collaboration, and we propose how researchers can take advantage of these recent developments.

Small islands that depend on limited freshwater resources are at significant risk from seasonal drought, which poses a major threat to both their ecosystems and communities. Christmas Island, located in the eastern Indian Ocean, presents an example for which severe drought conditions during the wet season not only affects its freshwater resources but also biodiversity on the island, including the migration pattern of the iconic red crab species. However, short-term instrumental climate records on this island make it hard to quantify drought variability and assess its associated risks. Tree growth is affected by drought via reduced soil moisture, and hydroclimate reconstruction from tree-ring chronologies can therefore provide longer-term information on historical variability of dry and wet periods. Here, we reconstructed the wet season (December-May) self-calibrating Palmer Drought Severity Index (scPDSI) for Christmas Island using 64 remote tree-ring chronologies from Asia, Australia, and New Zealand. scPDSI was reconstructed using the Point-to-Point Regression (PPR) method and compared with regional marine coral proxies for independent verification. The remote tree-ring chronologies explained more than 66 percent of scPDSI variance (R-squared) over the calibration period. The trees identified as significant predictors in the regression model were primarily located in areas affected by the Indo-Pacific climate drivers including the Indian Ocean Dipole (IOD). The reconstructions span 1540 CE to 2000. During the first four centuries of this period, the frequency of extreme (5th percentile) droughts and pluvial events rarely exceeded one event per 13 years. In contrast, the frequency of both extremes experienced an unprecedented increase during the 20th century, and with a notable shift towards dry conditions. These findings highlight a significant shift towards more frequent and severe dry conditions during the wet season on Christmas Island, posing a challenge to water resource management and potentially threatening the island's ecosystem and services to the community.

Long-standing interpretations of the Last Glacial Maximum (21,000 ± 2000 years ago) in Australia suggest that the period was extremely cold and arid, during which the Indo-Australian summer monsoon system collapsed, and human populations declined and retreated to ecological refuges to survive. Here, we use transient iTRACE simulations, combined with palaeoclimate proxy records and archaeological data to re-interpret the late Last Glacial Maximum and terminal Pleistocene (21,000 – 11,000 years) in Australia. The model suggests climates during the peak Last Glacial Maximum were cooler than present (−4 to −11 °C), but there is no evidence of monsoon collapse or substantial decreases in moisture balance across Australia. Kernel Density Estimates of archaeological ages show relatively stable and persistent human activity across most regions throughout the late Last Glacial Maximum and terminal Pleistocene, consistent with genetic evidence. Spatial coverage of archaeological sites steadily increased across the terminal Pleistocene; however, substantial population change is not evident.

The COVID-19 pandemic has caused significant disruptions to the world since 2020, with over 647 million confirmed cases and 6.7 million reported deaths as of January 2023. Despite its far-reaching impact, the effects of COVID-19 on the progress of global climate change negotiations have yet to be thoroughly evaluated. This discussion paper conducts an examination of COVID-19's impact on climate change actions at global, national, and local levels through a comprehensive review of existing literature. This analysis reveals that the pandemic has resulted in delays in implementing climate policies and altered priorities from climate action to the pandemic response. Despite these setbacks, the pandemic has also presented opportunities for accelerating the transition to a low-carbon economy. The interplay between these outcomes and the different levels of governance will play a crucial role in determining the success or failure of future climate change negotiations.

ABSTRACT Tree-ring series offer considerable potential for the development of environment-sensitive proxy records. However, with traditional increment cores, only small amounts of wood are often available from annual tree-ring sequences. For this reason, it is important to understand the reliability (and reproducibility) of radiocarbon measurements obtained from small-sized samples. Here we report the F 14 C results from the Chronos 14 Carbon-Cycle Facility of modern tropical Australian tree samples over a range of four graphite target sizes from the same rings. Our study shows that similar precision can be obtained from full-sized, half-sized, as well as small-sized graphite targets using standard pretreatment and analysis procedures. However, with a decline in sample size, there was an increase seen in the associated variance of the ages and the smallest target weights started showing a systematic bias. Wiggle-matching accuracy tests, comparing the Southern Hemisphere post-bomb atmospheric calibration curve to the different sample weight sequences, were all significant except for the 200 μgC graphite targets. Our results indicate that samples smaller than 350 μgC have limited accuracy and precision. Overall, reliable measurements of F 14 C sequences from tree-ring records across a range of sample sizes, with best results found using graphitized samples >350 μgC.

The Southern Hemisphere westerly winds (SWW), a belt of strong zonal winds in the mid-latitudes, play a key role in Southern Hemisphere climate variability. Recent intensification and southwards migration of the SWW is projected to continue due to anthropogenic climate change and despite a recovering Antarctic ozone hole, impacting regional hydroclimate, ocean circulation and carbon cycling. Despite the importance of the SWW, our understanding of their behaviour on centennial to millennial timescales is limited by the inherently short observational record and limited palaeo-archive agreement on the wind belt's Holocene dynamics. Here we utilise dust flux, Itrax core scanning, rare earth element composition and HYSPLIT particle modelling to present a 8700-year (10,500e170 0 cal yr BP) reconstruction of local SWW intensity from a Falkland Islands (Islas Malvinas) peat sediment core which, along with other reconstructions, we interpret in a regional South Atlantic and hemispheric context. We find increased dust deposition and variability from ca. 5700 cal yr BP, signalling an intensification and possible southwards shift of the SWW, though Patagonia likely remains the primary distal dust source throughout our record. Additionally, we identify asymmetric behaviour in the SWW belt from 3000 to 1700 cal yr BP over southern South America and the southwest Atlantic. In alignment with these findings, we propose a possible eastwards projection of the Amundsen Sea Low (ASL) into the South Atlantic during this period. Two volcanic eruptions, likely from Mt Burney (ca. 9700 cal yr BP) and Mt Hudson (ca. 4100 cal yr BP), are captured as cryptotephra deposits in the record. Our precisely dated, high-resolution multiproxy record of South Atlantic wind-blown transport provides an important new dataset that accurately constrains SWW Holocene variability over the Falkland Islands.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

ABSTRACT The IntCal family of radiocarbon ( 14 C) calibration curves is based on research spanning more than three decades. The IntCal group have collated the 14 C and calendar age data (mostly derived from primary publications with other types of data and meta-data) and, since 2010, made them available for other sorts of analysis through an open-access database. This has ensured transparency in terms of the data used in the construction of the ratified calibration curves. As the IntCal database expands, work is underway to facilitate best practice for new data submissions, make more of the associated metadata available in a structured form, and help those wishing to process the data with programming languages such as R, Python, and MATLAB. The data and metadata are complex because of the range of different types of archives. A restructured interface, based on the “IntChron” open-access data model, includes tools which allow the data to be plotted and compared without the need for export. The intention is to include complementary information which can be used alongside the main 14 C series to provide new insights into the global carbon cycle, as well as facilitating access to the data for other research applications. Overall, this work aims to streamline the generation of new calibration curves.

Interspecific variation in tree growth rate and maximum age is central to understanding and predicting the dynamics offorest ecosystems. While there are abundant sources ofthis information for economically important New Zealand timber species and other common tree species, data for trees from subantarctic environments are almost entirely lacking. Here we present measurements of growth from Auckland and Campbell Islands for three species: Metrosideros umbellata (southern rata; Myrtaceae, n = 1 site), a canopy dominant; Dracophyllum sp. (inaka; Ericaceae, n = 5 sites), a widespread small tree; and Olearia lyallii (tupare, subantarctic tree daisy; Asteraceae, n = 2 sites), a species native to Snares Island that has naturalised on the Auckland Islands. Our data showed large differences in tree growth rates among and within species across islands. Growth rates varied eight-fold (i.e. from 0.34 mm yr-1 to 2.78 mm yr-1), being greatest in Olearia lyallii , least in Dracophyllum sp. and intermediate in Metrosideros umbellata. Comparisons of the five Dracophyllum sites suggest that these trees experience reduced growth rates and reach older ages when in competition with the bigger southern rata (M. umbellata) trees, possibly due to the larger southern rata providing protection from wind-throw. Measurements of resprouted southern rata trees showed a variable juvenile-phase radial growth rate, highlighting the need for caution in extrapolating the likely ages of bigger trees. Remeasured individuals of Olearia lyallii growing among taller southern rata trees showed slow growth rates compared to much faster rates seen in a nearby monospecific stand. Overall, the variability in growth seen by all three species illustrates that tree size cannot be used to indicate age in these subantarctic islands.

<p>Droughts are a natural occurrence in many small Pacific Islands and can have severe impacts on local populations and environments. The El Niño-Southern Oscillation (ENSO) is a well-known driver of drought in the South Pacific, but our understanding of extreme ENSO events and their influence on island hydroclimate is limited by the short instrumental record and the infrequency of ENSO extremes. To address this gap, we present the South Pacific Drought Atlas (SPaDA), a multi-proxy, spatially resolved reconstruction of the November-April Standardised Precipitation Evapotranspiration Index for the southwest Pacific islands. The reconstruction integrates coral proxies, which provide local information on the South Pacific hydroclimate but are limited in number and length, with a network of continental tree-ring chronologies targeting Pacific climate variability through remote teleconnections. The reconstruction demonstrates the benefits of multi-proxy reconstructions incorporating tree rings, which allow for the alignment of other proxy records without chronological error.</p> <p>The SPaDA provides a 350-year, continuous dataset of climate information, which can be used to explore the occurrence of extreme events in the pre-instrumental period. The SPaDA closes the gap between existing paleo-reconstructions of point ENSO indices, and a spatially resolved drought atlas, allowing both the hydroclimate of individual islands and regional patterns of drought to be assessed. The benefit of a spatially resolved dataset to assess climate extremes in small Pacific islands is highlighted in the case of extreme El Niño events, which can have substantially different hydroclimatic impacts than more moderate events.</p> <p>We used an Isolation Forest, an unsupervised machine learning algorithm, to identify anomalous hydroclimatic states in the SPaDA that may indicate the occurrence of an extreme event. Extreme El Niño events characterised by very strong southwest Pacific drought anomalies and a zonal South Pacific Convergence Zone orientation are shown to have occurred semi-regularly throughout the reconstruction interval, providing a valuable baseline to compare to climate model projections. By identifying the spatial patterns of drought resulting from extreme events, we can better understand the impacts these events may have on individual Pacific Islands in the future.</p>

Managing water security and sustaining ecosystem functions under future warming poses substantial challenges for semi-arid regions. The Murray–Darling Basin (MDB) is particularly vulnerable given the considerable demand for water that underpins Australia’s agricultural production and contribution to the national economy. Understanding future drought risk requires a robust assessment of natural variability in drought length, frequency, and magnitude. In the absence of long instrumental records, past drought characteristics can be inferred from paleo-records. We reconstruct over 800 years of Murray River streamflow using a suite of tree-ring chronologies from regions with strong climate teleconnections to the MDB. The reconstruction (1190–2000 CE) captures a broad spectrum of natural climate variability, not fully represented in instrumental records, contributing to an improved understanding of the occurrence rate of multi-year droughts. We found that the Millennium Drought, which occurred in the 2000s, was the most severe (joint duration, magnitude, and peak) during the 800-year reconstruction. The return period of this event is estimated to be ∼2500 years. However, droughts in the early-1200s were of a longer duration and similar magnitude to the Millennium Drought. We used climate models to assess how the occurrence probability of severe droughts might change in the future. Compared to the 800-year baseline, climate models project an increase in future drought severity. While the increase in drought occurrence is within the uncertainty range for most future projections, the driest forecast shows a significant increase in the likelihood of severe droughts compared to natural variability. Our results highlight the need for water management strategies not to rely solely on instrumental data as it may not fully represent current and future risks. Ensuring a resilient MDB under future warming will require a robust water security policy that captures a broader range of natural and anthropogenic variability than currently recognised.

Long-term river discharge records are essential for water resource management, especially in semi-arid regions. However, the short instrumental records in Iran and the limited availability of local paleoclimate proxies to extend these records hinder our understanding of the full range of hydrologic variability. To help overcome these constraints, we have used annually-resolved tree-ring width chronologies from a network of sites spanning the eastern Mediterranean to the Tibetan Plateau to develop the first multi-centennial (similar to 500 years) river discharge reconstruction for the Dez River basin, a catchment that supports substantial water extraction in southwestern Iran. A Hierarchical Bayesian Regression (HBR) model accompanied by parsimonious predictor selection was used to derive the most robust model output. The selection method retained 26 precipitation-sensitive tree-ring width chronologies, mainly from regions with similar hydroclimate features to the Dez River basin. The resulting reconstruction of the most downstream gauging station accounts for 62% of the variance in river discharge observations, closely matching known historical events and other regional reconstructions. Notably, the un-derlying recurrence pattern of extreme flow conditions suggests floods were more frequent than low flow ex-tremes (i.e., droughts) during much of the 18th and early 19th centuries. In contrast, during the early 17th century, droughts were more frequent. Worryingly, the frequency of both floods and droughts has increased simultaneously since the beginning of the twentieth century. Our reconstruction could be used to assess current water allocation strategies under conditions similar to past extended dry periods. When combined with future projections, they can help provide more robust assessment scenarios for water management.

The evolutionarily recent dispersal of anatomically modern humans (AMH) out of Africa (OoA) and across Eurasia provides a unique opportunity to examine the impacts of genetic selection as humans adapted to multiple new environments. Analysis of ancient Eurasian genomic datasets (~1,000 to 45,000 y old) reveals signatures of strong selection, including at least 57 hard sweeps after the initial AMH movement OoA, which have been obscured in modern populations by extensive admixture during the Holocene. The spatiotemporal patterns of these hard sweeps provide a means to reconstruct early AMH population dispersals OoA. We identify a previously unsuspected extended period of genetic adaptation lasting ~30,000 y, potentially in the Arabian Peninsula area, prior to a major Neandertal genetic introgression and subsequent rapid dispersal across Eurasia as far as Australia. Consistent functional targets of selection initiated during this period, which we term the Arabian Standstill, include loci involved in the regulation of fat storage, neural development, skin physiology, and cilia function. Similar adaptive signatures are also evident in introgressed archaic hominin loci and modern Arctic human groups, and we suggest that this signal represents selection for cold adaptation. Surprisingly, many of the candidate selected loci across these groups appear to directly interact and coordinately regulate biological processes, with a number associated with major modern diseases including the ciliopathies, metabolic syndrome, and neurodegenerative disorders. This expands the potential for ancestral human adaptation to directly impact modern diseases, providing a platform for evolutionary medicine.