Hemisphere Climate Change Research Articles

Low-high latitude forcing on the East Asian winter monsoon evolution since the last glacial maximum

Abstract The East Asian winter monsoon (EAWM) has a profound effect on the winter climate in East Asia. The modern EAWM variability is tightly linked to the high-latitude Northern Hemisphere climate change through the Siberian High and can also be regulated by the low-latitude El Niño-Southern Oscillation through oceanic or atmospheric teleconnections. However, the Quaternary EAWM evolution has long been only attributed to the high-latitude climate change, resulting in the uncertainty in interpreting the out-of-phased EAWM variation recording in the East Asian continent and marginal seas. Here we presented a sediment record at Integrated Ocean Drilling Program Site U1427 in the southern Japan Sea to reconstruct the EAWM evolution since the last glacial maximum. By combining our record with previous reconstructions and simulations, we found the synchronous relationship between winter monsoon in northern and southern regions of East Asia from ∼24 to 8 ka, but anti-correlated relationship since ∼8 ka. We proposed the winter insolation and Atlantic meridional overturning circulation were the main drivers from last glacial to early Holocene, and then ENSO became a dominant factor in controlling the regional heterogeneity of EAWM evolution in the middle and late Holocene. This research explains much of the controversy in the Quaternary EAWM records and highlights the low-high latitude interaction in East Asian winter climate change.

Spatial and temporal variability in Holocene trough-fill sediments, King Haakon Trough System, sub-Antarctic South Georgia

The climate in the South Atlantic sector of the sub-Antarctic, and therefore on and around the island of South Georgia, is dependent on the Southern Hemisphere Westerlies (SHW) and the Antarctic Circumpolar Current (ACC). The SHW and the ACC, in turn, are strongly controlled by climate variability in the Southern Hemisphere. Accordingly, thick sediment sequences in the troughs across South Georgia's continental shelf serve as valuable archives for past climate variations in the Southern Ocean. Since Holocene climate fluctuations led to only minimal oscillations in glacier margin positions within the fjords, the entire shelf was exposed to dynamic ocean currents since at least 10 ka BP. Its depositional systems are therefore a suitable target for the reconstruction of Holocene dynamics of both the SHW and the ACC. Sub-bottom profiler data and radiocarbon ages from four gravity cores from the south-western South Georgia continental shelf provide evidence for a complex interplay between island run-off and ocean currents intruding into a unique cross-shelf trough system during the last ∼10 ka. The data reveal several prominent changes in sediment and Holocene climate dynamics, the most significant occurring between 8 and 7.7 cal ka BP and between 2.6 and 2.2 cal ka BP. Both of these time periods represent transitions from warmer to cooler and windier conditions in South Georgia and the Southern Hemisphere. Our record from the King Haakon Trough System is the first highly resolved Holocene archive from the marine realm on the south-western South Georgia continental shelf and suggests several large-scale Southern Hemisphere climate changes during the mid-to late Holocene.

Prescribing stratospheric chemistry overestimates southern hemisphere climate change during austral spring in response to quadrupled CO2

The interaction of stratospheric chemistry with a changing climate from an abrupt CO2 quadrupling is assessed using the coupled atmosphere–ocean Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). Two abrupt 4 × CO2 experiments were performed, one with interactive stratospheric chemistry and the other with a prescribed stratospheric chemistry that does not simulate stratospheric ozone response to 4 × CO2. The interactive and prescribed chemistry experiments simulate similar global mean surface temperature change. Nevertheless, interactive chemistry is critical to capture the Southern Hemisphere tropospheric midlatitude jet response to 4 × CO2. When stratospheric ozone response to 4 × CO2 is neglected, GEOSCCM overestimates Southern Hemisphere tropospheric circulation change. This stratospheric chemistry-induced climate impact has large seasonal variability. During the austral spring season September–October–November (SON), prescribed chemistry yields a stronger poleward shift and intensification of the Southern Hemisphere midlatitude tropospheric jet, surface wind stress, and the Southern Ocean meridional overturning circulation than occurs with interactive chemistry. In other seasons interactive and prescribed chemistry have similar effects on the Southern Hemisphere circulation. The seasonality of stratospheric chemistry-induced climate impact is related to the seasonality of Antarctic lower stratospheric ozone response to 4 × CO2. In contrast to this stratospheric ozone response to 4 × CO2, stratospheric ozone recovery from decline of the ozone depleting substances has its largest impact on the Southern Hemisphere tropospheric circulation in austral summer (December–January–February), but no effects in SON. It is found that the different seasonality for these two stratospheric ozone layer change scenarios is related to the different seasonality of tropopause meridional temperature gradient response.

Australian–Indonesian monsoon rainfall responses to the northern hemisphere climatic changes prior to the Last Glacial Maximum: an early indication

The evidences of Australian-Indonesian monsoon (AIM) rainfall response to the northern hemisphere climatic changes from both marine and terrestrial proxies are well established for the Last Glacial Maximum (LGM) – Deglaciation time interval but not in the previous time interval. Sediment cores from off south Sumba (ST10) and off north Sumba (Sumba strait) (ST14) were analyzed using X-Ray Fluorescence method to obtain elemental proxies. Elemental ratios which reflect terrigenous input (Ti/Ca and K/Ca) are used to infer the AIM rainfall changes since ~42 ka BP. AIM rainfall changes indicate a clear response to the Heinrich Events prior to the LGM (H2, H3, and H4). H2 and H3 are corroborated with the AIM rainfall increases in off south Sumba (~24 – 26 ka BP and ~30 – 31 ka BP) while the AIM rainfall increase (~39 – 41 ka BP) in the Sumba strait indicates a response to H4. The cooler temperature during the Heinrich Events could enhance the Northern Hemisphere (NH) cold surges which eventually pushed the Austral summer Intertropical Convergence Zone (ITCZ) southward in a similar fashion to the Last Deglaciation period (~18 – 11 ka BP). The southward movement of Austral summer ITCZ should increase the research area’s exposure time to the Tropical Rain Belt (TRB) during the Australian – Indonesian summer monsoon (AISM) which eventually triggers the AIM rainfall increase. The Sumba strait AIM rainfall unresponsiveness to H2 and H3 could be related to the constant exposure time to the TRB which indicates that the southern limit of Austral summer ITCZ during its northernmost shift didn’t reach the latitude of Sumba Strait. Comparison with other proxies from the same site and other rainfall proxies from southern Indonesia and the northern Australia regions is needed to confirm the spatial extend of those responses.

Separating the Influences of Low-Latitude Warming and Sea Ice Loss on Northern Hemisphere Climate Change

AbstractAnalyzing a multimodel ensemble of coupled climate model simulations forced with Arctic sea ice loss using a two-parameter pattern-scaling technique to remove the cross-coupling between low- and high-latitude responses, the sensitivity to high-latitude sea ice loss is isolated and contrasted to the sensitivity to low-latitude warming. Despite some differences in experimental design, the Northern Hemisphere near-surface atmospheric sensitivity to sea ice loss is found to be robust across models in the cold season; however, a larger intermodel spread is found at the surface in boreal summer, and in the free tropospheric circulation. In contrast, the sensitivity to low-latitude warming is most robust in the free troposphere and in the warm season, with more intermodel spread in the surface ocean and surface heat flux over the Northern Hemisphere. The robust signals associated with sea ice loss include upward turbulent and longwave heat fluxes where sea ice is lost, warming and freshening of the Arctic Ocean, warming of the eastern North Pacific Ocean relative to the western North Pacific with upward turbulent heat fluxes in the Kuroshio Extension, and salinification of the shallow shelf seas of the Arctic Ocean alongside freshening in the subpolar North Atlantic Ocean. In contrast, the robust signals associated with low-latitude warming include intensified ocean warming and upward latent heat fluxes near the western boundary currents, freshening of the Pacific Ocean, salinification of the North Atlantic, and downward sensible and longwave fluxes over the ocean.

Influence of Ozone Forcing on 21st Century Southern Hemisphere Surface Westerlies in CMIP6 Models

AbstractThe tropospheric westerly jet is a key feature of Southern Hemisphere climate. In recent decades the jet strengthened in austral summer (December–February [DJF]) and moved poleward owing to the Antarctic ozone hole. Future jet trends will be influenced by recovery of the Antarctic ozone hole and greenhouse gas (GHG) forcing. Here, we examine 21st century projections of ozone, temperature and winds in the sixth Coupled Model Intercomparison Project models with (CHEM) and without (NOCHEM) interactive chemistry. NOCHEM models use an ozone data set that was produced with GHG forcings inconsistent with those used by CHEM models, leading to less ozone recovery in the Antarctic springtime lower stratosphere. This propagates to different stratospheric temperature projections and DJF westerly winds: NOCHEM models project a 78 ± 52% stronger increase in DJF westerly wind speeds than CHEM models under the high GHG emissions scenario SSP585. Our results show the importance of simulating stratospheric ozone accurately for Southern Hemisphere climate change projections.

Spring Phenological Sensitivity to Climate Change in the Northern Hemisphere: Comprehensive Evaluation and Driving Force Analysis

Plant phenology depends largely on temperature, but temperature alone cannot explain the Northern Hemisphere shifts in the start of the growing season (SOS). The spatio–temporal distribution of SOS sensitivity to climate variability has also changed in recent years. We applied the partial least squares regression (PLSR) method to construct a standardized SOS sensitivity evaluation index and analyzed the combined effects of air temperature (Tem), water balance (Wbi), radiation (Srad), and previous year’s phenology on SOS. The spatial and temporal distributions of SOS sensitivity to Northern Hemisphere climate change from 1982 to 2014 were analyzed using time windows of 33 and 15 years; the dominant biological and environmental drivers were also assessed. The results showed that the combined sensitivity of SOS to climate change (SCom) is most influenced by preseason temperature sensitivity. However, because of the asymmetric response of SOS to daytime/night temperature (Tmax/Tmin) and non-negligible moderating of Wbi and Srad on SOS, SCom was more effective in expressing the effect of climate change on SOS than any single climatic factor. Vegetation cover (or type) was the dominant factor influencing the spatial pattern of SOS sensitivity, followed by spring temperature (Tmin > Tmax), and the weakest was water balance. Forests had the highest SCom absolute values. A significant decrease in the sensitivity of some vegetation (22.2%) led to a decreasing trend in sensitivity in the Northern Hemisphere. Although temperature remains the main climatic factor driving temporal changes in SCom, the temperature effects were asymmetric between spring and winter (Tems/Temw). More moisture might mitigate the asymmetric response of SCom to spring/winter warming. Vegetation adaptation has a greater influence on the temporal variability of SOS sensitivity relative to each climatic factor (Tems, Temw, Wbi, Srad). More moisture might mitigate the asymmetric response of SCom to spring/winter warming. This study provides a basis for vegetation phenology sensitivity assessment and prediction.

Multiple glacial maxima of similar extent at ∼20–45 ka on Mt. Usborne, East Falkland, South Atlantic region

The pattern, timing, and origin of Southern Hemisphere climate change during the last glaciation remains a pressing problem, with implications for the role of orbital forcing in ice-age cycles. Here, we present geomorphological and cosmogenic exposure age data from East Falkland in the South Atlantic region that show onset of glacial conditions by marine isotope stage 4 (∼60–70 ka), with expansion of ice to its maximum extent of the last glaciation. At least seven geomorphological units marked by multiple crests on composite moraines indicate glacier expansion on Mt. Usborne, the highest peak of East Falkland. From ∼20 to 45 ka, glaciers fluctuated on a millennial timescale with near-maximum conditions being reached repeatedly. Overall ice extent appears to have shrunk slightly through time, with evidence of glaciation at ∼20 ka preserved only in the highest-elevation cirques. This long glacial maximum is inconsistent both with local orbital control and orbital forcing as expressed in the traditional Milankovitch hypothesis. The timing of millennial glacier expansions occurred between Northern Hemisphere Heinrich Stadials and resembles that documented for New Zealand glaciers, suggesting at least a trans-Pacific expression. We postulate that periodic recessions corresponded with southward expansion of the southern westerlies during Heinrich Stadials and warming air and ocean temperatures over the South Atlantic region.

Sensitivity of the Atlantic Meridional Overturning Circulation to Model Resolution in CMIP6 HighResMIP Simulations and Implications for Future Changes

AbstractA multimodel, multiresolution ensemble using Coupled Model Intercomparison Project Phase 6 (CMIP6) High Resolution Model Intercomparison Project (HighResMIP) coupled experiments is used to assess the performance of key aspects of the North Atlantic circulation. The Atlantic Meridional Overturning Circulation (AMOC), and related heat transport, tends to become stronger as ocean model resolution is enhanced, better agreeing with observations at 26.5°N. However, for most models the circulation remains too shallow compared to observations and has a smaller temperature contrast between the northward and southward limbs of the AMOC. These biases cause the northward heat transport to be systematically too low for a given overturning strength. The higher‐resolution models also tend to have too much deep mixing in the subpolar gyre. In the period 2015–2050 the overturning circulation tends to decline more rapidly in the higher‐resolution models, which is related to both the mean state and to the subpolar gyre contribution to deep water formation. The main part of the decline comes from the Florida Current component of the circulation. Such large declines in AMOC are not seen in the models with resolutions more typically used for climate studies, suggesting an enhanced risk for Northern Hemisphere climate change. However, only a small number of different ocean models are included in the study.

Reconstruction of monsoon evolution in southernmost Sumatra over the past 35 kyr and its response to northern hemisphere climate changes

Reconstruction of monsoon evolution in the tropical Indian Ocean and evaluation of its influence on large-scale ocean circulation and sea-air interaction processes can help us understand climate driving mechanisms. Herein, we used a gravity core SO184-10043 to present the marine sedimentary record from the southernmost Sumatra, spanning the past 35 kyr. The age model is well constrained by 12 accelerator mass spectrometry (AMS) radiocarbon dates determined in mixed planktic foraminifera. We also measured sediment grain size and major and trace elements to reconstruct the variations in hydrodynamic conditions and chemical weathering intensity. These data were then used to reveal the evolution of the northwest (Indonesian) monsoon system over the past 35 kyr. The results showed that both monsoon current and chemical weathering coincided with summer insolation in the Northern Hemisphere and responded to glacial-interglacial climate changes in the northern Atlantic. Higher grain-size values of sensitive components, increased chemical index of alteration (CIA), and Ba/Sr ratios, together with lower CaO/MgO ratios, reflect a stronger monsoon current and chemical weathering during the late marine isotope stage 3 and Holocene. Higher intensity of chemical weathering might be attributed to a stronger northwest monsoon carrying warm and moist air from the Asian continent to Indonesian waters. Lower values of sensitive components, CIA, and Ba/Sr, along with higher CaO/MgO values, reveal a weaker monsoon current and lower intensity of chemical weathering during the last glaciation-deglaciation phase, which was controlled by a weaker monsoon system. At a millennial timescale, cold events occurred during the following intervals: 30–26 ka BP, Heinrich Stadial 1 (HS1; 18–15 ka BP), Last Glacial Maximum (LGM; 23–18 ka BP), Younger Dryas (YD; 11–10 ka BP), and 8.2 ka BP. The same cold events were identified from core SO184-10043, indicating a perfect match with climatic cooling in the Northern Hemisphere. We also observed periodicities of ~ 7.9 ka, 3.0–3.1 ka, 2.2–2.3 ka, and ~ 1.0 ka in our core records. These periodicities are coincident with solar-induced climate changes and support the hypothesis that monsoon evolution in the tropical Indian Ocean during the late Pleistocene coincided with the climate change in the Northern Hemisphere.

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.

The Early to late Middle Miocene mammalian assemblages from the Cura-Mallín Formation, at Lonquimay, southern Central Andes, Chile (~38°S): Biogeographical and paleoenvironmental implications

The Cura-Mallín Formation consists of a series of upper Oligocene to Upper Miocene volcanic and sedimentary rocks deposited in continental settings that crop out in the Andean Cordillera in Chile and Argentina between ~37° and 39°S. Since the 1990s few fossil mammals have been recovered from this unit in the surroundings of Lonquimay, south-central Chile (38.5°S), and all of them were assigned to the Early Miocene. After a reassessment of the taxonomic affinities of the fauna so far recovered from the Cura-Mallín Formation in the Lonquimay area, and based on the radioisotopic ages of the fossil-bearing localities, here we recognized two chronological distinctive mammalian assemblages: one of Early Miocene age (probably Colhuehuapian–Santacrucian SALMA), which includes Nesodon imbricatus and Parastrapotherium sp.; and a second one of late Middle Miocene age (12.8–11.6 Ma; Serravallian; Mayoan SALMA), which includes glyptodonts (Glyptodontidae indeterminate), armadillos (Eutatini indeterminate), macraucheniids (Theosodon sp.), a new interatheriid species (Protypotherium concepcionensis sp. nov.), and a likely platyrrhine monkey. Therefore, in contrast with previous interpretations, the fauna from Lonquimay is not uniquely restricted to the Early Miocene. The fossil mammals and plants recognized from the area indicate the persistence of mostly temperate and forested habitats with permanent bodies of water during the Early to latest Middle Miocene. This suggests that this part of the Andean Cordillera (38°‒39°S) did not reach enough paleoaltitudes (>1000 m) to cause an important orographic rain shadow effect in the foreland basins at least after the late Middle Miocene (c. 12 Ma). However, the role of Neogene South Hemisphere climatic changes in triggering, or reinforcing, the foreland desertification along the south-central Andes is an additional factor that cannot be discarded.

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.

Abrupt ice-age shifts in southern westerly winds and Antarctic climate forced from the north.

The mid-latitude westerly winds of the Southern Hemisphere play a central role in the global climate system via Southern Ocean upwelling1, carbon exchange with the deep ocean2, Agulhas leakage (transport of Indian Ocean waters into the Atlantic)3 and possibly Antarctic ice-sheet stability4. Meridional shifts of the Southern Hemisphere westerly winds have been hypothesized to occur5,6 in parallel with the well-documented shifts of the intertropical convergence zone7 in response to Dansgaard-Oeschger (DO) events- abrupt North Atlantic climate change events of the last ice age. Shifting moisture pathways to West Antarctica8 are consistent with this view but may represent a Pacific teleconnection pattern forced from the tropics9. The full response of the Southern Hemisphere atmospheric circulation to the DO cycle and its impact on Antarctic temperature remain unclear10. Here we use five ice cores synchronized via volcanic markers to show that the Antarctic temperature response to the DO cycle can be understood as the superposition of two modes: a spatially homogeneous oceanic 'bipolar seesaw' mode that lags behind Northern Hemisphere climate by about 200 years, and a spatially heterogeneous atmospheric mode that is synchronous with abrupt events in the Northern Hemisphere. Temperature anomalies of the atmospheric mode are similar to those associated with present-day Southern Annular Mode variability, rather than the Pacific-South American pattern. Moreover, deuterium-excess records suggest a zonally coherent migration of the Southern Hemisphere westerly winds over all ocean basins in phase with Northern Hemisphere climate. Our work provides a simple conceptual framework for understanding circum-Antarctic temperature variations forced by abrupt Northern Hemisphere climate change. We provide observational evidence of abrupt shifts in the Southern Hemisphere westerly winds, which have previously documented1-3 ramifications for global ocean circulation and atmospheric carbon dioxide. These coupled changes highlight the necessity of a global, rather than a purely North Atlantic, perspective on the DO cycle.

Hydrological variability in the western tropical Pacific over the past 700 kyr and its linkage to Northern Hemisphere climatic change

El Niño/Southern Oscillation (ENSO) events and latitudinal shifts of the Intertropical Convergence Zone (ITCZ) cause large scale hydrologic changes in the western tropical Pacific (WTP). However, there is still a debate on the role of ENSO and ITCZ shifts on the hydroclimate in the WTP and their linkage to Northern Hemisphere climate change on glacial-interglacial timescales. For that reason, we present ice volume-corrected seawater δ18O (δ18Osw-ice, a proxy for salinity) and sea surface temperature (SST) records from IMAGES Core MD06-3047B recovered from the northern WTP to investigate the hydroclimate in the WTP during the last 700kyr. Planktic foraminifera Globigerinoides ruber based Mg/Ca-SST and δ18Osw-ice records reveal distinct glacial-interglacial variations. The δ18Osw-ice record shows that our study site is characterized by fresher conditions and thus higher precipitation during glacials than during interglacials. Our results are in good agreement with numerical model simulations, which also suggest a glacial freshening in the northern WTP. A glacial freshening of the WTP is most likely related to a substantial weakening of the Atlantic Meridional Overturning Circulation (AMOC) and/or exposure of the Maritime Continent due to sea level changes which resulted in an enhanced Pacific Walker circulation and/or southward shift of the ITCZ. In addition, SST records from the WTP and the eastern tropical Pacific (ETP) suggest an enhanced tropical Pacific zonal SST gradient and thus La Niña-like conditions, which may have contributed to fresher conditions in the WTP during glacial periods. Besides, our rainfall record is in antiphase to the Chinese speleothem δ18O records, supporting the idea of an opposing trend in precipitation changes between the WTP and East Asia on orbital timescales.

Bay of Bengal Exhibits Warming Trend During the Younger Dryas: Implications of AMOC

AbstractA sharp decline in temperature during the Younger Dryas (YD) preceding the current warmer Holocene is well documented in climate archives from the Northern Hemisphere high latitudes. Although the magnitude of YD cooling varied spatially, the response of YD cooling was well documented in the Atlantic and Pacific Oceans but not in the Indian Ocean. Here we investigate whether the modern remote forcing of tropical Indian Ocean sea surface temperature (SST) by Northern Hemisphere climate changes holds true for events such as the YD. Our SST reconstruction from the western Bay of Bengal exhibits an overall warming of ∼1.8°C during the YD. We further compared our data with other existing Mg/Ca‐based SST records from the Northern Indian Ocean and found no significant negative SST anomalies in both the Arabian Sea and the Bay of Bengal compared to pre‐ and post‐YD, suggesting that no apparent cooling occurred during the YD in the Northern Indian Ocean. In contrast, most part of the YD exhibits positive SST anomalies in the Northern Indian Ocean that coincide with the slowdown of the Atlantic Meridional Overturning Circulation during this period.

The sustainability of water resources in High Mountain Asia in the context of recent and future glacier change

Abstract High Mountain Asia contains the largest volume of glacier ice outside the polar regions, and contain the headwaters of some of the largest rivers in central Asia. These glaciers are losing mass at a mean rate of between –0.18 and –0.5 m water equivalent per year. While glaciers in the Himalaya are generally shrinking, those in the Karakoram have experienced a slight mass gain. Both changes have occurred in response to rising air temperatures due to Northern Hemisphere climate change. In the westerly influenced Indus catchment, glacier meltwater makes up a large proportion of the hydrological budget, and loss of glacier mass will ultimately lead to a decrease in water supplies. In the monsoon-influenced Ganges and Brahmaputra catchments, the contribution of glacial meltwater is relatively small compared to the Indus, and the decrease in annual water supplies will be less dramatic. Therefore, enhanced glacier melt will increase river flows until the middle of the twenty-first century, but in the longer term, into the latter part of this century, river flows will decline as glaciers shrink. Declining meltwater supplies may be compensated by increases in precipitation, but this could exacerbate the risk of flooding.

The impact of Last Glacial climate variability in west-European loess revealed by radiocarbon dating of fossil earthworm granules

The characterization of Last Glacial millennial-timescale warming phases, known as interstadials or Dansgaard-Oeschger events, requires precise chronologies for the study of paleoclimate records. On the European continent, such chronologies are only available for several Last Glacial pollen and rare speleothem archives principally located in the Mediterranean domain. Farther north, in continental lowlands, numerous high-resolution records of loess and paleosols sequences show a consistent environmental response to stadial-interstadial cycles. However, the limited precision and accuracy of luminescence dating methods commonly used in loess deposits preclude exact correlations of paleosol horizons with Greenland interstadials. To overcome this problem, a radiocarbon dating protocol has been developed to date earthworm calcite granules from the reference loess sequence of Nussloch (Germany). Its application yields a consistent radiocarbon chronology of all soil horizons formed between 47 and 20 ka and unambiguously shows the correlation of every Greenland interstadial identified in isotope records with specific soil horizons. Furthermore, eight additional minor soil horizons dated between 27.5 and 21 ka only correlate with minor decreases in Greenland dust records. This dating strategy reveals the high sensitivity of loess paleoenvironments to Northern Hemisphere climate changes. A connection between loess sedimentation rate, Fennoscandian ice sheet dynamics, and sea level changes is proposed. The chronological improvements enabled by the radiocarbon "earthworm clock" thus strongly enhance our understanding of loess records to a better perception of the impact of Last Glacial climate changes on European paleoenvironments.

Glacial terminations and the Last Interglacial in the Okhotsk Sea; Their implication to global climatic changes

Paleoclimate data from the Okhotsk Sea (OS) over Terminations II and I (TII, TI), and the Last and Present Interglacial (LIG, PIG) periods were compiled in order to examine Northern Hemisphere climate and sea level changes. Based on records of four AMS 14C-dated OS cores over TI-PIG, it is argued that the OS productivity/climate, IRD (ice-rafted debris), and benthic foraminiferal oxygen isotope (δ18Obf) proxies provide representative and in-phase evidence of the Northern Hemisphere climate and continental ice sheet changes consistent with the LR 04 δ18Obf curve. Chronologies for two central OS cores over TII-LIG-cooling event 23 (C23) were constructed by correlating OS productivity proxies with well-dated δ18O records of Chinese speleothems because OS environment is modulated by East Asian Monsoon; and, as well as correlating measured magnetic paleointensity excursions with those in the dated PISO-1500 paleointensity stack. Results show several OS climatic and environment states, including TII coeval with Asian Weak Monsoon Interval (WMI) II since 136ka, LIG with a sharp two-step transition (130.2–129ka) and demise at С25 (116.5ka), and last glaciation with coolings at C24 (111ka) and C23. The OS productivity and IRD records demonstrate certain climate amelioration in the middle of WMI-II, and two insignificant cooling events inside the LIG marked by C27 (126ka) and C26 (120.6ka). OS δ18Obf records of both cores demonstrate a gradual trend of lighter values since around 131.5kaBP, continuing from the onset of LIG (129ka) to minimum values at 126kaBP (C27), then nearly constant values until 121.5ka, followed by a slight increase up to 120.6ka (C26), and a subsequent strong increase up to 116.5ka (C25). The magnitude of OS δ18Obf oscillations is 1.35‰, which is less than those in the N. Atlantic. It may therefore be suggested that this OS index probably tracks changes in continental ice sheet volume and sea level.

Ice core and climate reanalysis analogs to predict Antarctic and Southern Hemisphere climate changes

A primary goal of the SCAR (Scientific Committee for Antarctic Research) initiated AntClim21 (Antarctic Climate in the 21st Century) Scientific Research Programme is to develop analogs for understanding past, present and future climates for the Antarctic and Southern Hemisphere. In this contribution to AntClim21 we provide a framework for achieving this goal that includes: a description of basic climate parameters; comparison of existing climate reanalyses; and ice core sodium records as proxies for the frequencies of marine air mass intrusion spanning the past ∼2000 years. The resulting analog examples include: natural variability, a continuation of the current trend in Antarctic and Southern Ocean climate characterized by some regions of warming and some cooling at the surface of the Southern Ocean, Antarctic ozone healing, a generally warming climate and separate increases in the meridional and zonal winds. We emphasize changes in atmospheric circulation because the atmosphere rapidly transports heat, moisture, momentum, and pollutants, throughout the middle to high latitudes. In addition, atmospheric circulation interacts with temporal variations (synoptic to monthly scales, inter-annual, decadal, etc.) of sea ice extent and concentration. We also investigate associations between Antarctic atmospheric circulation features, notably the Amundsen Sea Low (ASL), and primary climate teleconnections including the SAM (Southern Annular Mode), ENSO (El Nino Southern Oscillation), the Pacific Decadal Oscillation (PDO), the AMO (Atlantic Multidecadal Oscillation), and solar irradiance variations.