Hemisphere Climate Research Articles

Holocene variability in sea ice and primary productivity in the northeastern Baffin Bay

Arctic sea ice is a critical component of the climate system, known to influence ocean circulation, earth’s albedo, and ocean–atmosphere heat and gas exchange. Current developments in the use of IP25 (a sea ice proxy with 25 carbon atoms only synthesized by Arctic sea ice diatoms) have proven it to be a suitable proxy for paleo-sea ice reconstructions over hundreds of thousands to even millions of years. In the NE Baffin Bay, off NW Greenland, Melville Bugt is a climate-sensitive region characterized by strong seasonal sea ice variability and strong melt-water discharge from the Greenland Ice Sheet (GIS). Here, we present a centennial-scale resolution Holocene sea ice record, based on IP25 and open-water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III) using core GeoB19927-3 (73° 35.26′ N, 58° 05.66′ W). Seasonal to ice-edge conditions near the core site are documented for most of the Holocene period with some significant variability. In the lower-most part, a cold interval characterized by extensive sea ice cover and very low local productivity is succeeded by an interval (~ 9.4–8.5 ka BP) with reduced sea ice cover, enhanced GIS spring melting, and strong influence of the West Greenland Current (WGC). From ~ 8.5 until ~ 7.8 ka BP, a cooling event is recorded by ice algae and phytoplankton biomarkers. They indicate an extended sea ice cover, possibly related to the opening of Nares Strait, which may have led to an increased influx of Polar Water into NE-Baffin Bay. The interval between ~ 7.8 and ~ 3.0 ka BP is characterized by generally reduced sea ice cover with millennial-scale variability of the (late winter/early spring) ice-edge limit, increased open-water conditions (polynya type), and a dominant WGC carrying warm waters at least as far as the Melville Bugt area. During the last ~ 3.0 ka BP, our biomarker records do not reflect the late Holocene ‘Neoglacial cooling’ observed elsewhere in the Northern Hemisphere, possibly due to the persistent influence of the WGC and interactions with the adjacent fjords. Peaks in HBI III at about ~ 2.1 and ~ 1.3 ka BP, interpreted as persistent ice-edge situations, might correlate with the Roman Warm Period (RWP) and Medieval Climate Anomaly (MCA), respectively, in-phase with the North Atlantic Oscillation (NAO) mode. When integrated with marine and terrestrial records from other circum-Baffin Bay areas (Disko Bay, the Canadian Arctic, the Labrador Sea), the Melville Bugt biomarker records point to close ties with high Arctic and Northern Hemispheric climate conditions, driven by solar and oceanic circulation forcings.

Impacts of extremely asymmetrical polar ice sheets on the East Asian summer monsoon during the MIS-13 interglacial

Marine Isotope Stage (MIS) 13 (∼500 ka ago) was a relatively weak interglacial according to the benthic δ18O and Antarctic ice core records. However, proxy records from the Northern Hemisphere indicate that MIS-13 was at least as warm as or even warmer than more recent interglacials, with an extremely strong summer monsoon and possible melting of the Greenland ice sheet. In this study, assuming an asymmetric hemispheric climate, we investigate the response of the East Asian summer monsoon to various Greenland and Antarctic ice sheet sizes using a set of sensitivity experiments with the HadCM3 model through factor separation analysis. Results show that with no Greenland ice sheet and a large Antarctic ice sheet there is an enhancement of summer monsoon precipitation in the East Asian monsoon region of up to ∼7%, in agreement with the direction of change from proxy reconstructions for China. This enhancement is associated with a stronger land–sea thermal contrast, more water vapor transport to East Asia and a northward shift of the Intertropical Convergence Zone. The response to the Greenland ice sheet removal is related to thermodynamic and topographical effects that influence the East Asian monsoon through an orographically induced wave train. The response to the larger Antarctic ice sheet involves stronger upwelling of circumpolar deep water in the Southern Ocean melts the sea ice, leading to a warmer SST. This warming propagates to the North, affecting the East Asian summer monsoon.

A quantitative temperature reconstruction of the ‘Little Ice Age’ in southern China

We present a branched glycerol dialkyl glycerol tetraethers (brGDGTs)–based mean annual temperature reconstruction covering the last millennium from a subtropical lake in Guangxi Province, southern China (23°N). We demonstrate that the pattern and absolute values of mean annual temperatures reconstructed using the eastern African lake brGDGTs calibration based on the methylation of 5-methyl branched tetraethers index provided the most reliable and accurate temperature estimates from the site. The results resemble regional and Northern Hemisphere changes over this period. The pattern shows a general cool period between ca. AD 1450 and 1950, including cooling minima centred at ca. AD 1600, 1750 and 1900, coeval with the ‘Little Ice Age’ temperature fluctuations in the Northern Hemisphere, followed by a warming trend from the mid-20th century to the present. The results suggest that both solar forcing and high-latitude Northern Hemisphere climate fluctuations play a role in influencing the terrestrial temperatures in southern China, possibly on different timescales. In addition, our results support the hypothesis that changes of the East Asian summer monsoon are primarily driven by the land–sea thermal gradient change between terrestrial southern China and the Indo-Pacific Warm Pool regions during the last millennium, owing to external radiative and/or volcanic forcings.

Трансформация пространственной структуры поля приземной температуры Северного полушария

The selection of informative criteria and objective classification methods is the current task of climatology. In this paper we present the results of the clustering algorithm of climate. The temperature signals are classified by the degree of similarity of the phase modulation characteristics. Different time periods were considered. They correspond to the main trends in the global temperature dynamics. Such an approach may be a variant of the objective dynamic classification of the Northern Hemisphere climate. Data from 818 meteorological stations were used. The transformation of the system and changes in the degree of temperature dynamics’ consistency at different intervals of years are revealed. This made it possible to identify the most sensitive areas of the Northern Hemisphere. In these areas the stations changed its structural affiliation depending on global trends. With increasing global temperature, the structure of the regional fields is changing. Coherence of temperature fluctuations varies. There is a transition of many stations of more northern classes to more southern ones. The most sensitive to global climate trends are the territories of Fennoscandia and Central Europe, Greenland, the Russian Arctic and Subarctic, Florida Peninsula, and stations located in a mountainous terrain Eurasian areas and areas of influence of basic centers of atmospheric action.

Born migrators: Historical biogeography of the cosmopolitan family Cannabaceae

AbstractDispersal scenarios have been favored over tectonic vicariance as an explanation for disjunct distributions in many plant taxa during the last two decades. However, this argument has been insufficiently addressed in cosmopolitan groups showing disjunct patterns in both the temperate and tropical regions. In this study, we used the Cannabaceae, an angiosperm family distributed in tropical and temperate regions of both the New World and the Old World, to explore the role of dispersal in shaping disjunct patterns and species diversification of cosmopolitan plants. We reconstructed the phylogenetic relationships of all 10 genera and 75 species of Cannabaceae (ca. 64.1% of recognized species) based on eight DNA regions. Based on fossil calibrations, we estimated the divergence times and net diversification rates. We further inferred the ancestral geographical ranges with several models and compared the fitness of different models. The Cannabaceae and most genera were strongly supported as monophyletic except for the Parasponia being embedded within the Trema. The Celtis were resolved into two strongly supported clades primarily corresponding to temperate and tropical regions. We inferred that the Cannabaceae originated at ca. 93 Ma, and that subsequent rampant and widespread dispersals shaped the intercontinentally disjunct distribution of the Cannabaceae. Dispersal coincides with adaptation to drier and colder climate in the Northern Hemisphere, or humid and warm climate in the tropical regions, followed by rapid species diversification. This study advances our understanding as to the formation of distribution patterns and species diversification of a plant family with tropical to temperate disjunct distributions.

Hydroclimate in the Pamirs Was Driven by Changes in Precipitation‐Evaporation Seasonality Since the Last Glacial Period

AbstractThe Central Asian Pamir Mountains (Pamirs) are a high‐altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial‐interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31‐kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. δD values of terrestrial biomarkers showed insolation‐driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive δD shifts driven by changes in precipitation seasonality were observed at ca. 31–30, 28–26, and 17–14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation‐evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.

Complexity in crisis: The volcanic cold pulse of the 1690s and the consequences of Scotland's failure to cope

Recent work has linked historical crises, both regional and local, with palaeoclimatic estimates of global and hemispheric climate change. Such studies tend to underemphasize the spatiotemporal and socioeconomical disparity of human suffering and adaptive capacity as well as the complexities of past climate change. We focus herein on the effects in Scotland of a severely cold climate episode in the 1690s, associated with major tropical volcanic events including a large unidentified tropical eruption in 1695. A tree-ring based summer temperature reconstruction from the northern Cairngorms region identifies the 1690s as the coldest decade in Scotland for the last 750 years. Archival sources meanwhile reveal the 1690s as likely the worst era of crop failure, food shortage, and mortality ever documented in Scottish history. The connection appears simple - volcanic cooling triggered famine - but the drivers towards famine are far more complex. Although the unusual coldness of the 1690s was near-hemispheric in scale, it had a differential impact across north-western Europe. Within Scotland, both lowlands and highlands experienced dire conditions, but distinct factors exacerbated the suffering in each region. We integrate historical and palaeoclimatic records to explore the influence of the volcanic cold pulse of the 1690s and its consequences in Scotland. We find that while cooling temperatures characterized the regional to larger-scale climate, vulnerability and response potential were diverse and shaped by local circumstances. The Scottish crisis of the 1690s, in the context of the kingdom's failing economy, influenced investors from all parts of society, including the nobility and entire communities, to fund the ill-fated expedition to colonize Darien in modern-day Panama. The climate crisis and the colony's collapse hindered Scotland's already sluggish economy, motivating unification with England soon after.

Potential contribution of winter dominant atmospheric mode over the mid‐latitude Eurasia to the prediction of subsequent spring Arctic Oscillation

AbstractSpring Arctic Oscillation (AO) has been revealed to exert a great impact on the Northern Hemispheric climate; however, its seasonal prediction skill has been limited so far. In this paper, we find that the dominant mode of the winter 500‐hPa geopotential height anomalies over the mid‐latitude Eurasia has a close connection with the succeeding spring AO. The analysis on the physical processes indicates that the troposphere–stratosphere interaction plays an important role in the connection between the two. This predominant atmospheric mode in the mid‐latitude Eurasia during winter can change the vertical wave activity and lead to an anomalous stratospheric polar vortex. Thereafter, the signal of the anomalous stratospheric polar vortex propagates downward to troposphere in the subsequent spring, consequently inducing the anomalous AO pattern in the troposphere. The results in this study imply that this previous winter leading atmospheric mode over the mid‐latitude Eurasia may supply a potential source for a spring AO's prediction.

Climate and ecology of the palaeo-Agulhas Plain from stable carbon and oxygen isotopes in bovid tooth enamel from Nelson Bay Cave, South Africa

We measured δ13Cenamel and δ18Oenamel in 213 archaeological bovid teeth from Nelson Bay Cave (NBC), spanning the last 22 ka. We also recorded dental mesowear (occlusal relief [high versus low] and cusp shape [sharp, round, or blunt]) of all maxillary first and second molars from NBC. We use these values to explore glacial/interglacial shifts in bovid palaeoecology and to reconstruct aspects of the climate and environment of the Palaeo-Agulhas Plain. Our results indicate that at the time of the Last Glacial Maximum (LGM), there was a significantly greater proportion of C3 (winter-rainfall) grasses, although some C4 (summer rainfall) varieties were present. This conclusion is strengthened by correction for lower pCO2 at the LGM, leading to reduced carbon isotope fractionation in C3 photosynthesis. Terminal Pleistocene and Holocene grazers show a stronger C4 signal. Our findings are consistent with an eastwards extension of winter rainfall at the LGM, as proposed by some previous researchers. Beyond the broad distinction between browsers and grazers, δ13C values reflect species-specific dietary preferences. δ18O is more positive in browsers than grazers, probably due to their deriving a significant proportion of their water intake from evaporatively enriched leaf water. δ18O values do not show significant changes through time. The location of Nelson Bay Cave on the present-day interface between temperate and tropical weather systems means that this area is sensitive to past shifts in the relative importance of these systems. These findings therefore contribute to the reconstruction of past Southern Hemisphere climate dynamics on a glacial/interglacial time scale.

Verification and Improvement of the Capability of ENSEMBLES to Predict the Winter Arctic Oscillation

AbstractThe winter Arctic Oscillation (AO) is important for understanding the Northern Hemisphere climate variability and predictability. However, ENSEMBLES models produce inconsistent predictions when applied to the interannual variability of the 1962–2006 winter AO. In this study, the interannual increment of the winter AO index (DY_AOI) during 1962–2006 is first improved by a dynamical‐statistical model with two predictors: the preceding autumn Arctic sea ice and the concurrent winter ENSEMBLES‐predicted sea surface temperature over the North Pacific. Next, the improved final AOI is obtained by adding the improved DY_AOI to the preceding observed AOI. Because the interannual increment approach can amplify prediction signals and takes advantage from the previous observed AOI, this method shows promise for significantly improving the interannual variability prediction capabilities of the winter AO during 1962–2006 in the ENSEMBLES models. Therefore, this study offers important insights for AO predictions, even other climate variables predictions.

Holocene glacier fluctuations on the northern flank of Cordillera Darwin, southernmost South America

Records of past variability afford context for evaluating present-day glacier behavior and for testing hypotheses of climate change. Here, we use 69 radiocarbon dates of wood and other organic materials in association with glacial deposits to document the behavior of Ventisqueros Marinelli and Brooks in Cordillera Darwin over the past ∼17,000 years. Recession from the last glacial maximum was early, with most occurring prior to 17,000 yr BP. Any glacial resurgence during the Antarctic Cold Reversal must have terminated within the bounds of Holocene ice fluctuations. By early Holocene time, Ventisquero Marinelli had retreated such that it was no more extensive than it was in AD 1992. We identify several subsequent glacier readvances, but also note long periods of restricted ice extent, particularly in the mid-Holocene. There were times when Holocene glaciers must have been smaller than at present. Our new record from Marinelli shows similarities to other reconstructions of Holocene glacier variation from southern South America, such as at Mt. Sarmiento and the South Patagonian Icefield, suggesting an underlying climate signal. The overall implication is of substantial early Holocene deglaciation followed by repeated advances interspersed with periods of recession when ice extent was smaller than at present. This general pattern of glacier behavior appears to differ from that of New Zealand's Southern Alps and points to the value of a geographic spread of datasets to elucidate the pattern of Southern Hemisphere climate during the Holocene.

The Linear Sensitivity of the North Atlantic Oscillation and Eddy-Driven Jet to SSTs

Abstract The North Atlantic Oscillation (NAO) and eddy-driven jet contain a forced component arising from sea surface temperature (SST) variations. Due to large amounts of internal variability, it is not trivial to determine where and to what extent SSTs force the NAO and jet. A linear statistical–dynamic method is employed with a large climate ensemble to compute the sensitivities of the winter and summer NAO and jet speed and latitude to the SSTs. Key regions of sensitivity are identified in the Indian and Pacific basins, and the North Atlantic tripole. Using the sensitivity maps and a long observational SST dataset, skillful reconstructions of the NAO and jet time series are made. The ability to skillfully forecast both the winter and summer NAO using only SST anomalies is also demonstrated. The linear approach used here allows precise attribution of model forecast signals to SSTs in particular regions. Skill comes from the Atlantic and Pacific basins on short lead times, while the Indian Ocean SSTs may contribute to the longer-term NAO trend. However, despite the region of high sensitivity in the Indian Ocean, SSTs here do not provide significant skill on interannual time scales, which highlights the limitations of the imposed SST approach. Given the impact of the NAO and jet on Northern Hemisphere weather and climate, these results provide useful information that could be used for improved attribution and forecasting.

Variations in ozone and greenhouse gases as drivers of Southern Hemisphere climate in a medium-complexity global climate model

The climate of the Southern Hemisphere (SH) is being affected not only by the global increase in the concentration of greenhouse gases (GHG) but also by the ongoing recovery of stratospheric ozone. The competing roles of both are usually studied by means of state-of-the-art global climate models (GCM) due to the complexity in the atmospheric processes and interactions involved. The main objective of this paper is to determine whether quantitatively similar results can be achieved using a simpler, medium-complexity GCM. This includes addressing the sensitivity of the medium-complexity model to changes in GHG and ozone concentrations as well as looking into the plausible mechanisms driving such patterns of variations in atmospheric circulation, precipitation and temperature extremes. Two sets of simulations are performed: one with fixed sea surface temperatures (SST) and another one making use of a mixed-layer ocean model coupled to the GCM. Results show that the GCM is highly sensitive to changes in the atmospheric composition, and that the largest differences are found when SST are allowed to vary accordingly, particularly in the case of temperature extremes. Specific analyses are also performed on changes in subtropical precipitation over the continental regions of the SH, with moisture budget decomposition being applied in order to provide explanations for the rainfall changes described in the manuscript.

Climate cycles in the southern Levant and their global climatic connections

The history of Levant paleo-hydrology, which is expressed by the absolute water level record of the Dead Sea over the last 70 kyrs, has been shown to be closely coupled with global climate patterns, and specifically argued to be modulated by northern hemisphere climate systems. Here, this coupling is rigorously tested and the absolute lake level curve is compared with a variety of globally distributed climate archives and used to deconvolve the processes controlling regional climate and hydrology. Considering that different archives are based on different sampling resolutions, and hence might have inherently different recording sensitivities, each of the chosen archives was interpolated and then smoothed at varying temporal resolutions. The synthetic curves, ranging between temporal smoothing resolutions between 10 years and 15 kyrs were compared to the similarly processed lake level record over the last 60 kyrs. The best fit to the Dead Sea lake level was found to be with Antarctica temperatures and atmospheric CO2 levels. Greenland temperatures and proximal archives such as the Soreq Cave and the Dead Sea lithological record, all yielded weaker correlations to the lake level curve.An exception to the strong correlation between Levant climate and atmospheric CO2 concentrations, is observed during Marine Isotope Stage (MIS) 5e, at a time when the Dead Sea watershed was exposed to very weak Mediterranean westerly systems that imposed hyperarid conditions, and a superposition of southern derived systems that delivered short but intense precipitation to the region. At this time, Antarctic temperatures cross a temperature threshold beyond 1 °C above present. It is suggested that this exceptional warming phase induces a reorganization of global and regional climate systems influencing the Levant.These results have two important implications. The first is the understanding that global temperatures and atmospheric CO2 concentrations impose the first order control over Levant climate. The second, is that the Antarctic records can be used as synthetic lake level proxies, extending the absolute lake level curve to ca. 800 ka, compared with its current span of 70 kyrs. Considering the importance of the Dead Sea lake level curve as a regional paleo-climatic-hydrologic recorder, the new synthetic curve provides a prominent proxy of Levant hydro-climate history.

Multimodel Analysis of the Atmospheric Response to Antarctic Sea Ice Loss at Quadrupled CO2

AbstractAntarctic sea ice cover is projected to significantly decrease by the end of the twenty‐first century if greenhouse gas concentrations continue to rise, with potential consequences for Southern Hemisphere weather and climate. Here we examine the atmospheric response to projected Antarctic sea ice loss at quadrupled CO2, inferred from 11 Coupled Model Intercomparison Project phase 5 models. Our study is the first multimodel analysis of the atmospheric response to Antarctic sea ice loss. Projected sea ice loss enhances the negative phase of the Southern Annular Mode, which slightly damps the positive Southern Annular Mode response to increased CO2, particularly in spring. The negative Southern Annular Mode response largely reflects a weakening of the eddy‐driven jet, and to a lesser extent, an equatorward shift of the jet. Sea ice loss induces near‐surface warming over the high‐latitude Southern Ocean, but warming does not penetrate over the Antarctic continent. In spring, we find multimodel evidence for a weakened polar stratospheric vortex in response to sea ice loss.

Radiocarbon and geologic evidence reveal Ilopango volcano as source of the colossal ‘mystery’ eruption of 539/40 CE

Ilopango volcano (El Salvador) erupted violently during the Maya Classic Period (250–900 CE) in a densely-populated and intensively-cultivated region of the southern Maya realm, causing regional abandonment of an area covering more than 20,000 km2. However, neither the regional nor global impacts of the Tierra Blanca Joven (TBJ) eruption in Mesoamerica have been well appraised due to limitations in available volcanological, chronological, and archaeological observations. Here we present new evidence of the age, magnitude and sulfur release of the TBJ eruption, establishing it as one of the two hitherto unidentified volcanic triggers of a period of stratospheric aerosol loading that profoundly impacted Northern Hemisphere climate and society between circa 536 and 550 CE. Our chronology is derived from 100 new radiocarbon measurements performed on three subfossil tree trunks enveloped in proximal TBJ pyroclastic deposits. We also reassess the eruption magnitude using terrestrial (El Salvador, Guatemala, Honduras) and near-shore marine TBJ tephra deposit thickness measurements. Together, our new constraints on the age, eruption size (43.6 km3 Dense Rock Equivalent of magma, magnitude = 7.0) and sulfur yield (∼9–90 Tg), along with Ilopango's latitude (13.7° N), squarely frame the TBJ as the major climate-forcing eruption of 539 or 540 CE identified in bipolar ice cores and sourced to the tropics. In addition to deepening appreciation of the TBJ eruption's impacts in Mesoamerica, linking it to the major Northern Hemisphere climatic downturn of the mid-6th century CE offers another piece in the puzzle of understanding Eurasian history of the period.

Antarctic iceberg impacts on future Southern Hemisphere climate

Future iceberg and meltwater discharge from the Antarctic ice sheet (AIS) could substantially exceed present levels, with strong implications for future climate and sea levels. Recent climate model simulations on the impact of a rapid disintegration of the AIS on climate have applied idealized freshwater forcing scenarios1,2 rather than the more realistic iceberg forcing. Here we use a coupled climate–iceberg model to determine the climatic effects of combined iceberg latent heat of fusion and freshwater forcing. The iceberg forcing is derived from an ensemble of future simulations conducted using the Penn State ice-sheet model3. In agreement with previous studies, the simulated AIS meltwater forcing causes a substantial delay in greenhouse warming in the Southern Hemisphere and activates a transient positive feedback between surface freshening, subsurface warming and ice-sheet/shelf melting, which can last for about 100 years and may contribute to an accelerated ice loss around Antarctica. However, accounting further for the oceanic heat loss due to iceberg melting considerably increases the surface cooling effect and reduces the subsurface temperature feedback amplitude. Our findings document the importance of considering realistic climate–ice sheet–iceberg coupling for future climate and sea-level projections. Climate change will increase meltwater and iceberg discharge from Antarctica, with implications for future climate and sea levels. Iceberg melt will partly offset greenhouse warming in the Southern Ocean and dampen the positive feedback loop between ice-sheet melting and subsurface warming.

Influence of December snow cover over North America on January surface air temperature over the midlatitude Asia

AbstractThe impact of North American (NA) snow cover on the Northern Hemisphere climate has drawn increasing attention in recent years. This study reveals a negative relationship between NA snow cover in December and surface air temperature (SAT) over the midlatitude Asia in the following January. The results show that, in December, the extensive snow cover decreases SAT over NA via local diabatic cooling, which further intensifies the Atlantic jet stream by enlarging the meridional gradient of the 1,000‐ to 300‐hPa layer thickness, especially along 40°N. Meanwhile, we found negative sea surface temperature (SST) anomalies over the Western North Atlantic and enhanced transient eddy activity over the Eastern North Atlantic due to anomalous net energy conversion from the mean flow. In January, a zonally oriented dipole of transient eddy anomalies straddles the North Atlantic, with the negative–positive (west–east) anomaly centres attributing to local oceanic cooling and the persistence of the eddy–mean flow interaction, respectively. Such dipole of transient eddy activity in turn favours the downstream development of the Atlantic jet stream. Besides, the changes in surface turbulent heat flux over the North Atlantic trigger a Rossby wave train that propagates across Europe and towards the Far East. Coincident with the strengthened Siberian High and the accelerated East Asian jet stream in January, SAT decreases over the midlatitude Asia. Hence, our analysis indicates that December NA snow cover could potentially be exploited for subseasonal predictability over Asia.

Modeling the 1783–1784 Laki Eruption in Iceland: 2. Climate Impacts

AbstractThe Laki eruption in Iceland, which began in June 1783, was followed by many of the typical climate responses to volcanic eruptions: suppressed precipitation and drought, crop failure, and surface cooling. In contrast to the observed cooling in 1784–1786, the summer of 1783 was anomalously warm in Western Europe, with July temperatures reaching more than 3 K above the mean. However, the winter of 1783–1784 in Europe was as cold as 3 K below the mean. While climate models generally reproduce the surface cooling and decreased rainfall associated with volcanic eruptions, model studies have failed to reproduce the extreme warming in western Europe that followed the Laki eruption. As a result of the inability to reproduce the anomalous warming, the question remains as to whether this phenomenon was a response to the eruption or merely an example of internal climate variability. Using the Community Earth System Model from the National Center for Atmospheric Research, we investigate the “Laki haze” and its effect on Northern Hemisphere climate in the 12 months following the eruption onset. We find that the warm summer of 1783 was a result of atmospheric blocking over Northern Europe, which in our model cannot be attributed to the eruption. In addition, the extremely cold winter of 1783–1784 was aided by an increased likelihood of an El Niño after the eruption. Understanding the causes of these anomalies is important not only for historical purposes but also for understanding and predicting possible climate responses to future high‐latitude volcanic eruptions.

Asynchronous Variation in the Quaternary East Asian Winter Monsoon Associated With the Tropical Pacific ENSO‐Like System

AbstractQuaternary East Asian winter monsoon (EAWM) evolution has long been attributed to high‐latitude Northern Hemisphere climate change. However, it cannot explain the distinct relationships of the EAWM in the northern and southern East Asian marginal sea in paleoclimatic records. Here we present an EAWM record of the northern East China Sea over the past 300 ka and a transient climate simulation with the Kiel Climate Model through the Holocene. Both proxy record and simulation suggest anticorrelated long‐term EAWM evolution between the northern East China Sea and the South China Sea. We suggest that this spatial discrepancy of EAWM can be interpreted as El Niño–Southern Oscillation (ENSO)‐like controlling, which generates cyclonic/anticyclonic wind anomalies in the northern/southern East Asian marginal sea. This research explains much of the controversy in nonorbital scale variability of Quaternary EAWM records in the East Asian marginal sea and supports a potent role of tropical forcing in East Asian winter climate change.