Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
The Arctic, Antarctic, and Greenland
ABSTRACT: Observational evidence suggests that river inflows to the Arctic Ocean have increased over the last 30 years. Continued increases have the potential to alter the freshwater balance in the Arctic and North Atlantic Oceans and hence the thermohaline circulation. Simulations with a macroscale hydrological model and climate change scenarios derived from six climate models and two emissions scenarios suggest increases of up to 31% in river inflows to the Arctic by the 2080s under high emissions and up to 24% under lower emissions, although there are large differences between climate models. Uncertainty analysis suggests low sensitivity to model form and parameterization but higher sensitivity to the input data used to drive the model. The addition of up to 0.048 sverdrup (Sv, 106 m3 s-1 ) is a large proportion of the 0.06–0.15 Sv of additional freshwater that may trigger thermohaline collapse. Changes in the spatial distribution of inflows to the Arctic Ocean may influence circulation patterns within the ocean.
FIRST PARAGRAPH: Observations of warming in the high northern latitudes provide a variety of scientific datasets to better understand the forcings and feedbacks at work in the global climate system. Instrumental data and satellites show that most of the current Arctic warming is the result of large changes in winter temperatures and that, by comparison, changes in summer temperatures have been relatively modest (1). Yet changes in seasonal temperatures are having a profound influence on glaciers, sea ice cover, snow cover, nutrient flux, and vegetation assemblages, causing shifts in both terrestrial and marine ecosystems (2, 3). Profoundly provocative is the suggestion that rapid melt rates now observed at the margins of the Greenland Ice Sheet (GIS) still lag significantly behind recent Northern Hemisphere warming (4).
Cortese, G., A. Abelmann, R. Gersonde (2007). The last five glacial-interglacial transitions: A high-resolution 450,000-year record from the subantarctic Atlantic. Paleoceanography 22 (PA4203): doi:10.1029/2007PA001457
ABSTRACT: A submillennial resolution, radiolarian-based record of summer sea surface temperature (SST) documents the last five glacial to interglacial transitions at the subtropical front, southern Atlantic Ocean. Rapid fluctuations occur both during glacial and interglacial intervals, and sudden cooling episodes at glacial terminations are recurrent. Surface hydrography and global ice volume proxies from the same core suggest that summer SST increases prior to terminations lead global ice-volume decreases by 4.7 ± 3.7 ka (in the eccentricity band), 6.9 ± 2.5 ka (obliquity), and 2.7 ± 0.9 ka (precession). A comparison between SST and benthicd13 C suggests a decoupling in the response of northern subantarctic surface, intermediate, and deep water masses to cold events in the North Atlantic. The matching features between our SST record and the one from core MD97-2120 (southwest Pacific) suggests that the super-regional expression of climatic events is substantially affected by a single climatic agent: the Subtropical Front, amplifier and vehicle for the transfer of climatic change. The direct correlation between warmerDTsite at Vostok and warmer SST at ODP Site 1089 suggests that warmer oceanic/atmospheric conditions imply a more southward placed frontal system, weaker gradients, and therefore stronger Agulhas input to the Atlantic Ocean.
ABSTRACT: Freshwater discharge to high-latitude oceans in 64 Canadian rivers is investigated. The mean annual discharge rate attains 1252 km3 yr-1 for an area of 5.6 × 106 km2 , equating to a sink of 225 mm yr-1 in the surface water budget of northern Canada (excluding the Arctic Archipelago where insufficient data exist). Application of the Mann-Kendall test to the data reveals a 10% decrease (-125 km3 yr-1 or -22 mm yr-1 ) in the total annual river discharge to the Arctic and North Atlantic Oceans from 1964 to 2003. This trend in river runoff is consistent with a 21 mm yr-1 decline in observed precipitation over northern Canada between 1964 and 2000. We find evidence of statistically-significant links between the Arctic Oscillation, El Niño/Southern Oscillation, and the Pacific Decadal Oscillation to the total annual freshwater discharge in northern Canada's rivers at interannual-to-decadal timescales.
D. Fisher, A. Dyke, R. Koerner, J. Bourgeois, C. Kinnard, C. Zdanowicz, A. de Vernal, C. Hillaire-Marcel, J. Savelle, A. Rochon (2006). Natural variability of Arctic sea ice over the Holocene. EOS, Transactions of the American Geophysical Union 87 (28): 3 pp.
ABSTRACT: A consortium of Canadian groups is using ocean cores, ice cores, and mammalian and archeological histories to build a Holocene sea ice history; preliminary results are reported in this article.
ABSTRACT: Abrupt changes in climate, termed Dansgaard-Oeschger and Heinrich events, have punctuated the last glacial period (~100-10 kyr ago) but not the Holocene (the past 10 kyr). Here we use an intermediate-complexity climate model to investigate the stability of glacial climate, and we find that only one mode of Atlantic Ocean circulation is stable: a cold mode with deep water formation in the Atlantic Ocean south of Iceland. However, a 'warm' circulation mode similar to the present-day Atlantic Ocean is only marginally unstable, and temporary transitions to this warm mode can easily be triggered. This leads to abrupt warm events in the model which share many characteristics of the observed Dansgaard-Oeschger events. For a large freshwater input (such as a large release of icebergs), the model's deep water formation is temporarily switched off, causing no strong cooling in Greenland but warming in Antarctica, as is observed for Heinrich events. Our stability analysis provides an explanation why glacial climate is much more variable than Holocene climate.
ABSTRACT: Accurate simulation of ice-sheet surface mass balance requires higher spatial resolution than is afforded by typical atmosphere–ocean general circulation models (AOGCMs), owing, in particular, to the need to resolve the narrow and steep margins where the majority of precipitation and ablation occurs. We have developed a method for calculating mass-balance changes by combining ice-sheet average time-series from AOGCM projections for future centuries, both with information from high-resolution climate models run for short periods and with a 20 km ice-sheet mass-balance model. Antarctica contributes negatively to sea level on account of increased accumulation, while Greenland contributes positively because ablation increases more rapidly. The uncertainty in the results is about 20% for Antarctica and 35% for Greenland. Changes in ice-sheet topography and dynamics are not included, but we discuss their possible effects. For an annual- and area-average warming exceeding 4.5 ± 0.9 K in Greenland and 3.1 ± 0.8 K in the global average, the net surface mass balance of the Greenland ice sheet becomes negative, in which case it is likely that the ice sheet would eventually be eliminated, raising global-average sea level by 7m.
FIRST PARAGRAPH: The Greenland ice-sheet would melt faster in a warmer climate and is likely to be eliminated — except for residual glaciers in the mountains — if the annual average temperature in Greenland increases by more than about 3 °C. This could raise the global average sea-level by 7 metres over a period of 1,000 years or more. We show here that concentrations of greenhouse gases will probably have reached levels before the year 2100 that are sufficient to raise the temperature past this warming threshold.
ABSTRACT: 1] Analysis of new data for eight stations in coastal southern Greenland, 1958–2001, shows a significant cooling (trend-line change -1.29°C for the 44 years), as do sea-surface temperatures in the adjacent part of the Labrador Sea, in contrast to global warming (+0.53°C over the same period). The land and sea temperature series follow similar patterns and are strongly correlated but with no obvious lead/lag either way. This cooling is significantly inversely correlated with an increased phase of the North Atlantic Oscillation (NAO) over the past few decades (r= -0.76), and will probably have significantly affected the mass balance of the Greenland Ice Sheet.
ABSTRACT: An ice age model is proposed in which glacial-interglacial global climatic cycles are controlled by interactions between the cryosphere, hydrosphere, and atmosphere in the Atlantic environment. In the model, climatic change results from instabilities which develop in the snowfields or ice sheets of North America, Europe, and Antarctica. Disintegration of the West Antarctic ice sheet (that portion of the Antarctic ice sheet lying in the western hemisphere) initiates a chain of events which culminates in a global ice age. Ten independent bodies of data can be interpreted as evidence that the West Antarctic ice sheet has been and is disintegrating. The dynamics of the Ross Sea ice drainage system of Antarctica is examined to determine what controls disintegration and recovery of the West Antarctic ice sheet. It is concluded that disintegration is controlled by ice streams which drain the inherently unstable West Antarctic ice sheet and recovery is controlled by outlet glaciers which drain the inherently stable East Antarctic ice sheet. Glacial stability in both cases is determined by the degree of coupling between the ice sheet and its bed. Ice drainage channels develop when this coupling is weakened normal to the margin of an ice sheet and can lead to surges in ice streams or outlet glaciers. Ice shelves develop when this coupling is weakened parallel to the margin of an ice sheet and can lead to a rapid grounding line retreat of floating ice tongues or ice shelves. An inflection maximum on the ice sheet surface migrates inland during a surge and migrates seaward after the surge is spent. A transition zone between the ice sheet and the ice shelf widens during a grounding line retreat inland and narrows during a grounding line advance seaward. Inflection line and grounding line migrations combine to give the ice sheet a concave surface during retreat and a convex surface during advance. A train of surging segments in an ice stream lowers the ice sheet in stages, creating a terraced ice stream surface which causes rapid discontinuous retreats of the grounding line. Rapid glacial recovery following a surge can truncate the advancing ice sheet-ice shelf boundary. Today at least one West Antarctic ice stream is terraced and at least one East Antarctic outlet glacier is truncated in the Ross Sea ice drainage system. If this condition is general, the West Antarctic ice sheet is disintegrating along the Siple Coast as a result of surging ice streams and is recovering along the Transantarctic Mountains as a result of thickening outlet glaciers. The competition between these processes will provide a critical test of the ice age model, which predicts that progressive disintegration of the West Antarctic ice sheet results in progressive growth of adjacent parts of the East Antarctic ice sheet.
ABSTRACT: New calculations were performed to investigate the combined response of the Greenland and Antarctic ice sheets to a range of climatic warming scenarios over the next millennium. Use was made of fully dynamic 3D thermomechanic ice sheet models, which were coupled to a two-dimensional climate model. The experiments were initialized with simulations over the last two glacial cycles to estimate the present evolution and were subsequently forced with temperature scenarios resulting from greenhouse emission scenarios which assume equivalent CO2 increases of two, four, and eight times the present (1990 a.d.) value by the year 2130 a.d. and a stabilization after that. The calculations brought to light that during the next century (short-term effect), the background evolution trend would dominate the response of the Antarctic ice sheet but would be negligible for the Greenland ice sheet. On that timescale, the Greenland and Antarctic ice sheets would roughly balance one another for the middle scenario (similar to the IPCC96 IS92a scenario), with respective contributions to the worldwide sea level stand on the order of about ±10 cm. On the longer term, however, both ice sheets would contribute positively to the worldwide sea level stand and the most important effect would come from melting on the Greenland ice sheet. Sensitivity experiments highlighted the role of ice dynamics and the height–mass-balance feedback on the results. It was found that ice dynamics cannot be neglected for the Greenland ice sheet, not even on a century timescale, but becomes only important for Antarctica on the longer term. The latter is related to an increased outflow of ice into the ice shelves and to the grounding-line retreat of the west Antarctic ice sheet, which are both found to be sensitive to basal melting below ice shelves and the effective viscosity of the ice shelves. Stretching parameters to their limits yielded a combined maximum rate of sea level rise of 85 cm century−1 , of which 60 cm would originate from the Greenland ice sheet alone.
ABSTRACT: Freshwater (FW) leaves the Arctic Ocean through sea-ice export and the outflow of low-salinity upper ocean water. Whereas the variability of the sea-ice export is known to be mainly caused by changes in the local wind and the thickness of the exported sea ice, the mechanisms that regulate the variability of the liquid FW export are still under investigation. To better understand these mechanisms, we present an analysis of the variability of the liquid FW export from the Arctic Ocean for the period 1950–2007, using a simulation from an energy and mass conserving global ocean–sea ice model, coupled to an Energy Moisture Balance Model of the atmosphere, and forced with daily winds from the NCEP reanalysis. Our results show that the simulated liquid FW exports through the Canadian Arctic Archipelago (CAA) and the Fram Strait lag changes in the large-scale atmospheric circulation over the Arctic by 1 and 6 years, respectively. The variability of the liquid FW exports is caused by changes in the cyclonicity of the atmospheric forcing, which cause a FW redistribution in the Arctic through changes in Ekman transport in the Beaufort Gyre. This in turn causes changes in the sea surface height (SSH) and salinity upstream of the CAA and Fram Strait, which affect the velocity and salinity of the outflow. The SSH changes induced by the large-scale atmospheric circulation are found to explain a large part of the variance of the liquid FW export, while the local wind plays a much smaller role. We also show that during periods of increased liquid FW export from the Arctic, the strength of the simulated Atlantic meridional overturning circulation is reduced and the ocean heat transport into the Arctic is increased. These results are particularly relevant in the context of global warming, as climate simulations predict an increase in the liquid FW export from the Arctic during the twenty-first century.
Johannessen, O.M., L. Bengtsson, M.W. Miles, S.I. Kuzmina, V.A. Semenov, G.V. Alekseev, A.P. Nagurnyi, V.F. Zakharov, L.P. Bobylev, L.H. Pettersson, K. Hasselmann, H.P. Cattle (2004). Arctic climate change: observed and modelled temperature and sea-ice variability. Tellus Series A - Dynamic Meteorology and Oceanography 56 (4): 328-341
ABSTRACT: Changes apparent in the arctic climate system in recent years require evaluation in a century-scale perspective in order to assess the Arctic's response to increasing anthropogenic greenhouse-gas forcing. Here, a new set of century- and multidecadal-scale observational data of surface air temperature (SAT) and sea ice is used in combination with ECHAM4 and HadCM3 coupled atmosphere–ice–ocean global model simulations in order to better determine and understand arctic climate variability. We show that two pronounced twentieth-century warming events, both amplified in the Arctic, were linked to sea-ice variability. SAT observations and model simulations indicate that the nature of the arctic warming in the last two decades is distinct from the early twentieth-century warm period. It is suggested strongly that the earlier warming was natural internal climate-system variability, whereas the recent SAT changes are a response to anthropogenic forcing. The area of arctic sea ice is furthermore observed to have decreased ~8 × 105 km2 (7.4%) in the past quarter century, with record-low summer ice coverage in September 2002. A set of model predictions is used to quantify changes in the ice cover through the twenty-first century, with greater reductions expected in summer than winter. In summer, a predominantly sea-ice-free Arctic is predicted for the end of this century.
ABSTRACT: The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.
ABSTRACT: The oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on Earth — the ice sheets and the oceans. Since the latest of these oscillations, the Last Glacial Maximum (between about 30,000 and 19,000 years ago), 50 million cubic kilometres of ice has melted from the land-based ice sheets, raising global sea level by 130 metres. Such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere, oceans, ice sheets and solid earth, all of which have different response timescales. The trigger for the sea-level fluctuations most probably lies with changes in insolation, caused by astronomical forcing, but internal feedback cycles complicate the simple model of causes and effects.
ABSTRACT: A time series of surface melt extent, frequency and onset has been updated to include data from Electrically Scanning Microwave Radiometer (ESMR) (1973, 1974 and 1976), Scanning Multichannel Microwave Radiometer (SMMR) (1979–1987) and the Special Sensor Microwave/Imager (SSM/I) (1987–2007). The seasonal melt departure (SMD), the sum from 1 June to 31 August of the departure from average of each day's melt extent, is a new metric used to describe the amount of melt. Results show a large increase in melt in summer 2007, 60% more than the previous high in 1998. During summer 2007, some locations south of 70°N had as many as 50 more days of melt than average. Melt occurred as much as 30 days earlier than average. The SMD is shown to be significantly related to temperatures at coastal meteorological stations, although 2007 had more melt than might be expected based on the summer temperature record.
J.T. Overpeck, B. L. Otto-Bliesner, G. H. Miller, D. R. Muhs, R. B. Alley, J. T. Kiehl (2006). Paleoclimatic evidence for future ice-sheet instability and rapid sea-level rise. Science 311 (5768): 1747-1750
ABSTRACT: Sea-level rise from melting of polar ice sheets is one of the largest potential threats of future climate change. Polar warming by the year 2100 may reach levels similar to those of 130,000 to 127,000 years ago that were associated with sea levels several meters above modern levels; both the Greenland Ice Sheet and portions of the Antarctic Ice Sheet may be vulnerable. The record of past ice-sheet melting indicates that the rate of future melting and related sea-level rise could be faster than widely thought.
ABSTRACT: Abrupt climatic oscillations around the North Atlantic have been identified recently in Greenland ice cores as well as in North Atlantic marine sediment cores. The good correlation between the"Dansgaard Oeschger events" in the ice and the "Heinrich events" in the ocean suggests climate, in the North Atlantic region, underwent several massive reorganizations in the last glacial period. A characteristic feature seems to be their hierarchical structure. Every 7 to 10-thousand years, when the temperature is close to its minimum, the ice-sheet undergoes a massive iceberg discharge. This Heinrich event is followed by an abrupt warming. then by other oscillations, each lasting between one and two thousand years. These secondary oscillations do not have a clear signature in marine sediments but constitute most of the "Dansgaard-Oeschger events" found in the ice. A simplified model coupling an ice-sheet and an ocean basin, to illustrate how the interactions between these two components can lead to such a hierarchical structure. The ice-sheet model exhibits internal oscillations composed of growing phases and basal ice melting phases that induce massive iceberg discharges. These fresh water inputs in the ocean stop for a moment the thermohaline circulation, enhancing the temperature contrast between low- and high-latitudes. Just after this event, the thermohaline circulation restarts and an abrupt warming of high-latitude regions is observed. For some parameter values, these warmer temperatures have some influence on the ice-sheet, inducing secondary oscillations similar to those found in paleoclimatic records. Although the mechanism presented here may be too grossly simplified. it nevertheless underlines the potential importance of the coupling between ice-sheet dynamics and oceanic thermohaline circulation on the structure of the climatic records during the last glacial period. 33 refs., 14 figs., 1 tab.
ABSTRACT: Recent advances in the determination of the mass balance of polar ice sheets show that the Greenland Ice Sheet is losing mass by near-coastal thinning, and that the West Antarctic Ice Sheet, with thickening in the west and thinning in the north, is probably thinning overall. The mass imbalance of the East Antarctic Ice Sheet is likely to be small, but even its sign cannot yet be determined. Large sectors of ice in southeast Greenland, the Amundsen Sea Embayment of West Antarctica, and the Antarctic Peninsula are changing quite rapidly as a result of processes not yet understood.
ABSTRACT: The oxygen isotope record from the Greenland Ice Sheet Project 2 (GISP2) ice core was reanalyzed in the frequency and time domains. The prominent 1470-year spectral peak, which has been associated with the occurrence of Dansgaard-Oeschger interstadial events, is solely caused by Dansgaard-Oeschger events 5, 6, and 7. This result emphasizes the nonstationary character of the oxygen isotope time series. Nevertheless, a fundamental pacing period of ~1470 years seems to control the timing of the onset of the Dansgaard-Oeschger events. A trapezoidal time series model is introduced which provides a template for the pacing of the Dansgaard-Oeschger events. Statistical analysis indicates only a =3% probability that the number of matches between observed and template-derived onsets of Dansgaard-Oeschger events between 13 and 46 kyr B.P. resulted by chance. During this interval the spacing of the Dansgaard-Oeschger onsets varied by ±20% around the fundamental 1470-year period and multiples thereof. The pacing seems unaffected by variations in the strength of North Atlantic Deep Water formation, suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period.
M. C. Serreze, J. A. Maslanik, T. A. Scambos, F. Fetterer, J. Stroeve, K. Knowles, C. Fowler, S. Drobot, R. G. Barry, T. M. Haran (2003). A record minimum arctic sea ice extent and area in 2002. Geophysical Research Letters 30 (3): doi:10.1029/2002GL016406
ABSTRACT: Arctic sea ice extent and area in September 2002 reached their lowest levels recorded since 1978. These conditions likely resulted from (1) anomalous warm southerly winds in spring, advecting ice poleward from the Siberian coast (2) persistent low pressure and high temperatures over the Arctic Ocean in summer, promoting ice divergence and rapid melt.
ABSTRACT: Changes in Arctic sea ice cover have the potential to impact midlatitude climate. A previous sensitivity study utilizing the National Center for Atmospheric Research’s (NCAR) atmospheric general circulation model [AGCM; Community Climate Model, version 3 (CCM3)] to explore climate sensitivity to declining Arctic sea ice cover suggested that, as Arctic sea ice cover is reduced, precipitation patterns over western North America will shift toward dryer conditions in southwestern North America and wetter conditions in northwestern North America. Here, three complementary lines of research validate and explore the robustness of this possible climate change impact: 1) repetition of the previous sensitivity study (specified constant Arctic sea ice cover and atmospheric CO2 ) with an updated version of the NCAR AGCM [third Community Atmosphere Model (CAM3)], 2) investigation of the climate response to dynamically reduced Arctic sea ice cover (driven by a quadrupling of atmospheric CO2 ) in the coupled NCAR Community Climate System Model (CCSMv3), and 3) analysis of similar results from six other coupled climate system models. Results from the CAM3 sensitivity study are similar to those from the original study with declining Arctic sea ice cover driving up to 25% less mean annual precipitation (MAP) over southwestern North America and up to an 8% increase in MAP over northwestern North America. The seven coupled models also reproduce this same general pattern. At the time of CO2 quadrupling, Arctic sea ice cover is reduced (up to 90% in boreal winter) and MAP over southwestern North America decreases by up to 30% while MAP in northwestern North America increases by up to 40%. These results represent a significant shift in the precipitation pattern over western North America and support the findings of the original sensitivity study in suggesting that, as future reductions in Arctic sea ice cover take place, there will be a substantial impact on water resources in western North America.
ABSTRACT: The present and future state of the Arctic sea ice cover is explored using new observations and a coupled one dimensional air–sea–ice model. Updated satellite observations of Fram Strait ice-area export show an increase over the last four years, with ~37% increase in winter 07–08. Atmospheric poleward energy flux declined since 1990, but advection of oceanic heat has recently increased. Simulations show that the ice area export is a stronger driver of thinning than the estimated ocean heat fluxes of 40 TW. Increased ocean heat transport will raise primarily Atlantic layer temperature. The ‘present 2007’ state of the Arctic ice could be a stable state given the recent high ice area export, but if ocean heat advection and ice export decrease, the ice cover will recover. A 2*CO2 scenario with export and oceanic heat flux remaining strong, forecasts a summer Arctic open ocean area of 95% around 2050.
ABSTRACT: A study of the isotopic and gas composition of the basal silty ice recovered by the Greenland Ice Core Project (GRIP) core indicates that local ice formed in the absence of the Greenland Ice Sheet is still preserved at Summit. Such ice developed most probably within a peat deposit in a permafrost environment. This local ice was subsequently intimately mixed with glacier ice from an advancing ice sheet progressing on the site. This is in agreement with the “highland origin and windward growth” hypothesis for ice sheet development, not for an in situ or regional growth from snowbanks. The basal ice from the GRIP core possibly dates back to the original buildup of the Greenland Ice Sheet 2.4 million years ago.
ABSTRACT: The Antarctic contribution to sea-level rise has long been uncertain. While regional variability in ice dynamics has been revealed, a picture of mass changes throughout the continental ice sheet is lacking. Here, we use satellite radar altimetry to measure the elevation change of 72% of the grounded ice sheet during the period 1992–2003. Depending on the density of the snow giving rise to the observed elevation fluctuations, the ice sheet mass trend falls in the range −5–+85 Gt yr−1 . We find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend—growth of 27±29 Gt yr−1 —is based on an assessment of the expected snowfall variability. Mass gains from accumulating snow, particularly on the Antarctic Peninsula and within East Antarctica, exceed the ice dynamic mass loss from West Antarctica. The result exacerbates the difficulty of explaining twentieth century sea-level rise.
ABSTRACT: The time series of volcanically produced sulfate from the GISP2 ice core is used to develop a continuous record of explosive volcanism over the past 110,000 yr. We identified ~850 volcanic signals (700 of these from 110,000 to 9000 yr ago) with sulfate concentrations greater than that associated with historical eruptions from either equatorial or mid-latitude regions that are known to have perturbed global or Northern Hemisphere climate, respectively. This number is a minimum because decreasing sampling resolution with depth, source volcano location, variable circulation patterns at the time of the eruption, and post-depositional modification of the signal can result in an incomplete record. The largest and most abundant volcanic signals over the past 110,000 yr, even after accounting for lower sampling resolution in the earlier part of the record, occur between 17,000 and 6000 yr ago, during and following the last deglaciation. A second period of enhanced volcanism occurs 35,000–22,000 yr ago, leading up to and during the last glacial maximum. These findings further support a possible climate-forcing component in volcanism. Increased volcanism often occurs during stadial/interstadial transitions within the last glaciation, but this is not consistent over the entire cycle. Ages for some of the largest known eruptions 100,000–9000 yr ago closely correspond to individual sulfate peaks or groups of peaks in our record.