The 852/3 CE eruption of Mount Churchill, Alaska, was one of the largest first-millennium volcanic events, with a magnitude of 6.7 (VEI 6) and a tephra volume of 39.4–61.9 km 3 (95 % confidence). The spatial extent of the ash fallout from this event is considerable and the cryptotephra (White River Ash east; WRAe) extends as far as Finland and Poland. Proximal ecosystem and societal disturbances have been linked with this eruption; however, wider eruption impacts on climate and society are unknown. Greenland ice core records show that the eruption occurred in winter 852/3 ± 1 CE and that the eruption is associated with a relatively moderate sulfate aerosol loading but large abundances of volcanic ash and chlorine. Here we assess the potential broader impact of this eruption using palaeoenvironmental reconstructions, historical records and climate model simulations. We also use the fortuitous timing of the 852/3 CE Churchill eruption and its extensively widespread tephra deposition of the White River Ash (east) (WRAe) to examine the climatic expression of the warm Medieval Climate Anomaly period (MCA; ca. 950–1250 CE) from precisely linked peatlands in the North Atlantic region. The reconstructed climate forcing potential of the 852/3 CE Churchill eruption is moderate compared with the eruption magnitude, but tree-ring-inferred temperatures report a significant atmospheric cooling of 0.8 ∘ C in summer 853 CE. Modelled climate scenarios also show a cooling in 853 CE, although t

Current warming and human activity have negatively impacted the hydrological budget of some of the larger lakes in the Balkan region. To explore potential climatic analogues for the recent climatic period we investigated a speleothem record from Golubarnica Cave in North Macedonia focusing on hydrological changes occurring during the Medieval Climatic Anomaly (MCA). The δ18O record and petrography identify a period of drier conditions between ca. 800 and 1250 CE, chronologically consistent with the MCA. This is broadly consistent with lake lowstands in lakes Prespa and Dojran obtained by geomorphological, sedimentological and diatom data, as well as increasing evaporation at lakes Prespa and Ohrid inferred by δ18O of endogenic lacustrine calcite. Taken together, these observations point to an extensive effect of the MCA-related hydrological anomaly over the Balkan region, which occurred during a period of persistent positive North Atlantic Oscillation (NAO). Our results offer an important analog for comparing the regional response under the ongoing pressure of global warming.

Within the last Millennium the transition between the Medieval Climate Anomaly (MCA; ca. 1000–1300 CE) and the Little Ice Age (LIA; ca. 1400–1800 CE) has been recorded in a global array of climatic and oceanographic proxies. In this study we review proxy evidence for two alternative hypotheses for the effects of this shift in the North Atlantic region. One hypothesis postulates that the MCA/LIA transition included a weakening of the Atlantic Meridional Overturning Circulation (AMOC) and a transi

Abstract A decadally resolved diatom record from a sediment core collected from Disko Bay, central West Greenland, reveals variations in hydrological conditions for the late Holocene. The diatom flora record two clear trends in surface water temperatures: a pronounced cooling of surface waters during the Medieval Climate Anomaly (MCA) and a progressive warming in surface waters during the Little Ice Age (LIA), previously identified in North Atlantic studies. Our data support the existence of a previously identified anti-phase relationship between surface water temperatures off West Greenland and climate events recorded in the north-east Atlantic. The diatom assemblages show relatively cool surface water conditions during warmer climatic intervals, e.g. 3.6–2.7 cal. ka BP, the MCA, while relatively warm surface water conditions during colder climatic periods, e.g. the Dark Ages (DA) and the LIA. The exception to this is the Roman Warm Period (RWP), which in West Greenland shows warmer surface waters and climatic conditions. Our data also show the existence of anti-phase relationship between surface and sub-surface water temperatures in Disko Bay during the interval 3.6–2.7 cal. ka BP (cooler surface with warmer subsurface waters) and towards the end of the LIA (warmer surface and cooler sub-surface waters). These anti-phases patterns are possibly linked to: 1) the local spring–summer hydrological conditions (e.g. warmer climatic intervals), such as meltwater flux from sea ice/

The Medieval Climate Anomaly (MCA; ca. 950–1250 CE) and the Little Ice Age (LIA; ca. 1450–1850 CE) were periods generally characterized by respectively higher and lower temperatures in many regions. However, they have also been associated with drier and wetter conditions in areas around the Intertropical Convergence Zone (ITCZ) and the Asian Monsoon region and in areas impacted by large-scale climatic modes like the Northern Annular Mode and Southern Annular Mode (NAM and SAM respectively). To analyze coordinated changes in large-scale hydroclimate patterns and whether similar changes also extend to other periods of the Last Millennium (LM) outside the MCA and the LIA, reconstruction-based products have been analyzed. This includes the collection of tree-ring-based drought atlases (DAs), the Paleo Hydrodynamics Data Assimilation product (PHYDA) and the Last Millennium Reanalysis (LMR). These analyses have shown coherent changes in the hydroclimate of tropical and extratropical regions, such as northern and central South America, East Africa, western North America, western Europe, the Middle East, Southeast Asia, and the Indo-Pacific, during the MCA, the LIA and other periods of the LM. Comparisons with model simulations from the Community Earth System Model – Last Millennium Ensemble (CESM-LME) and phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) show that both external forcing and internal variability contributed to these changes, with the contri

time period. Records show that the world's average temperature remained colder for at least a century afterwards. The Medieval Warm Period from 950 to 1250 In world history, post-classical history refers to the period from about 500 CE to about 1450 or 1500 CE, roughly corresponding to the European Middle Ages following the decline of the western Roman Empire. The post-classical period is characterized by the expansion of certain civilizations geographically, by ongoing wars fought over land, resources and religion, and by the development of trade ne There are shorter climate periods that could be said roughly to account for large scale climate trends in the post-classical period. These include the Late Antique Little Ice Age, the Medieval Warm Period and the Little Ice Age. The extreme weather events of 536–537 were likely initiated by the eruption of the Lake Ilopango caldera in El Salvador. Sulfate emitted into the air initiated global cooling, migrations and crop failures worldwide, possibly intensifying an already cooler time period. Records show that the world's average temperature remained colder for at least a century afterwards. The Medieval Warm Period from 950 to 1250 occurred mostly in the Northern…

Instrumental observations of subsurface ocean warming imply that ocean heat uptake has slowed 20th-century surface warming. We present high-resolution records from subpolar North Atlantic sediments that are consistent with instrumental observations of surface and deep warming/freshening and in addition reconstruct the surface-deep relation of the last 1200 years. Sites from ~1300 meters and deeper suggest an ~0.5 degrees celsius cooling across the Medieval Climate Anomaly to Little Ice Age transition that began ~1350 ± 50 common era (CE), whereas surface records suggest asynchronous cooling onset spanning ~600 years. These data suggest that ocean circulation integrates surface variability that is transmitted rapidly to depth by the Atlantic Meridional Ocean Circulation, implying that the ocean moderated Earth's surface temperature throughout the last millennium as it does today.

The High Arctic plays a vital role in Earth's climate system, and its ecosystems are highly sensitive to global climate change. High Arctic lakes are valuable sentinels of climate change, as their sediments integrate long-term natural climatic fluctuations and anthropogenic influences. Here, we present a high-resolution ∼5000 year-reconstruction of NE Greenland climate variability from Aucella Lake (74°N, 20°E) based on physical, chemical, and biological properties of lake sediments. We use CT-scans, hyperspectral imaging, organic matter, XRD, and diatom analyses to show that changing air temperatures were controlled by a mix of regional climatic changes and local landscape feedbacks. The latest Mid-Holocene (∼5.0-3.8 cal. ka BP) was characterized by relatively warmer conditions, while the onset of the Late-Holocene was marked by abrupt temperature decreases that coincided with the beginning of glacial advances elsewhere (∼3.8-3.4 cal. ka BP). From ∼3.4-2.4 cal. ka BP, the sedimentary record indicated progressive warming, with temperature peaking during the Medieval Climate Anomaly, although temperature rises were punctuated by abrupt, short-lived cold periods. From ∼1.1-0.05 cal. ka BP, the influence of landscape factors over the system diminished. Sedimentary indicators suggested a transition towards a colder, more humid climate, coinciding with the beginning of the Little Ice Age, that was characterized by a marked decrease in air temperature that reached minimum values at the end of this period. The last 50 years at Aucella Lake were marked by abrupt temperature rises, consistent with recently observed anthropogenic global warming. Our results illustrate the importance of high-resolution multiproxy studies for accurately characterizing lake linkages to their environment and climate.