Wildfires emit large quantities of particles that affect Earth's climate and human health. Black carbon (BC), commonly known as soot, is directly emitted to the atmosphere by wildfires and other processes and can be transported and deposited in remote regions including high‐altitude glaciers and the polar regions. Here, we present a continuous, high‐resolution record of BC and ammonium (NH 4 + ) from 1933 to 2001 extracted from two ice cores retrieved in 2002 from the col between Mt. Bona and Mt. Churchill in the Wrangell‐St. Elias Mountain Range, southeast Alaska. Despite the substantial increase of BC from fossil fuels in the Arctic since the Industrial Revolution, BC at Bona‐Churchill originates primarily from biomass burning and thus provides a record reflecting a fire history for Alaska. The BC record from Bona‐Churchill reveals that high fire activity became more frequent after 1984 in agreement with Alaska fire records. Most years associated with high BC or high NH 4 + before 1984 occurred during El Niño events when precipitation in Alaska was below “normal,” suggesting that precipitation played an important role in modulating fire activity in Alaska prior to the 1980s. Conversely, years with high BC or NH 4 + after 1984 coincided with years with “normal” and low precipitation, but elevated temperatures, strongly suggesting that temperature became a more dominant factor influencing fire activity in Alaska after the 1980s as suggested by other studies. Recent Alaska fire records and temperatures indicate that this trend has continued in the 21st century.

Ice cores from the northwestern Tibetan Plateau (NWTP) contain long records of regional climate variability, but refrozen meltwater and dust in these cores has hampered development of robust timescales. Here, we introduce an approach to dating the ice via the isotopic composition of atmospheric O2 in air bubbles (δ18Oatm), along with annual layer counting and radiocarbon dating. We provide a robust chronology for water isotope records (δ18Oice and d-excess) from three ice cores from the Guliya ice cap in the NWTP. The measurement of δ18Oatm, although common in polar ice core timescales, has rarely been used on ice cores from low-latitude, high-altitude glaciers due to (1) low air pressure, (2) the common presence of refrozen melt that adds dissolved gases and reduces the amount of air available for analysis, and (3) the respiratory consumption of molecular oxygen (O2) by micro-organisms in the ice, which fractionates the δ18O of O2 from the atmospheric value. Here, we make corrections for melt and respiration to address these complications. The resulting records of water isotopes from the Guliya ice cores reveal climatic variations over the last 15,000 y, the timings of which correspond to those observed in independently dated lake and speleothem records and confirm that the Guliya ice cap existed before the Holocene. The millennial-scale drivers of δ18Oice are complex and temporally variable; however, Guliya δ18Oice values since the mid-20th century are the highest since the beginning of the Holocene and have increased with regional air temperature.

Alpine glaciers in the low- and mid-latitudes respond more quickly than large polar ice sheets to changes in temperature, precipitation, cloudiness, humidity, and radiation. Many high-altitude glaciers are monitored by ground observations, aerial photography, and satellite-borne sensors. Regardless of latitude and elevation, nearly all nonpolar glaciers and ice caps are undergoing mass loss, which compromises the records of past climate preserved within them. Almost without exception, the retreat of these ice fields is persistent, and a very important driver is the recent warming of the tropical troposphere and oceans. Here we present data on the decrease in the surface area of four glaciers from low- to mid-latitude mountainous regions: the Andes of Peru and northern Bolivia, equatorial east Africa, equatorial Papua, Indonesia, and the western Tibetan Plateau. Climate records based on oxygen isotopic ratios (delta O-18) measured in ice cores drilled from several glaciers in these regions reveal that the records from elevations below similar to 6000 m above sea level have been substantially modified by seasonal melting and the movement of meltwater through porous upper firn layers. Fortunately, delta O-18 records recovered from higher altitude sites still contain well-preserved seasonal variations to the surface; however, the projected increase in the rate of atmospheric warming implies that climate records from higher elevation glaciers will eventually also be degraded. A long-term ice core collection program on the Quelccaya ice cap in Peru, Earth's largest tropical ice cap, illustrates that the deterioration of its climate record is concomitant with the increase in mid-troposphere temperatures. The melting ice and resulting growth of proglacial lakes presents an imminent hazard to nearby communities. The accelerating melting of glaciers, if sustained, ensures the eventual loss of unique and irreplaceable climate histories, as well as profound economic, agricultural, and cultural impacts on local communities.

Using an assemblage of four ice cores collected around the Pacific basin, one of the first basinwide histories of Pacific climate variability has been created. This ice core–derived index of the interdecadal Pacific oscillation (IPO) incorporates ice core records from South America, the Himalayas, the Antarctic Peninsula, and northwestern North America. The reconstructed IPO is annually resolved and dates to 1450 CE. The IPO index compares well with observations during the instrumental period and with paleo-proxy assimilated datasets throughout the entire record, which indicates a robust and temporally stationary IPO signal for the last ~550 years. Paleoclimate reconstructions from the tropical Pacific region vary greatly during the Little Ice Age (LIA), although the reconstructed IPO index in this study suggests that the LIA was primarily defined by a weak, negative IPO phase and hence more La Niña–like conditions. Although the mean state of the tropical Pacific Ocean during the LIA remains uncertain, the reconstructed IPO reveals some interesting dynamical relationships with the intertropical convergence zone (ITCZ). In the current warm period, a positive (negative) IPO coincides with an expansion (contraction) of the seasonal latitudinal range of the ITCZ. This relationship is not stationary, however, and is virtually absent throughout the LIA, suggesting that external forcing, such as that from volcanoes and/or reduced solar irradiance, could be driving either the ITCZ shifts or the climate dominating the ice core sites used in the IPO reconstruction.

Stable oxygen isotopes (δ18O) in the Bona‐Churchill (B‐C) ice core from southeast Alaska provide a valuable, high‐resolution history of climate variability and sea ice cover in the western Arctic over the last 800 years. Multiple ice cores have been collected from the Wrangell‐St. Elias Mountain Range; however, their δ18O records exhibit little consistency as each core offers a unique view on local, regional, and/or global climate variability. To explore the primary mechanisms influencing the isotopic signature at the B‐C site, we utilize isotope‐enabled model data, reanalysis data, and observations, which all indicate a strong connection between isotopes at the B‐C site and western Arctic climate, likely established by the location of the storm track in this region. Enriched B‐C δ18O reflects increased southerly flow and warmer waters in the Bering Sea, which modulates the heat flux through the Bering Strait and into the Arctic, thereby affecting sea ice cover in the western Arctic. The B‐C δ18O paleorecord shares some remarkable similarities (r = −0.80, p < .001) with the duration of western arctic sea ice cover reconstructed from a Chukchi Sea sediment core. Interestingly, during the Little Ice Age, enriched δ18O and reduced western Arctic sea ice are observed and may be indicative of prolonged periods of the warm Arctic/cold continents pattern and a northwestward shift of the North Pacific storm track.

Records of recent climate from ice cores drilled in 2015 on the Guliya ice cap in the western Kunlun Mountains of the Tibetan Plateau, which with the Himalaya comprises the Third Pole (TP), demonstrate that this region has become warmer and moister since at least the middle of the 19th century. Decadal-scale linkages are suggested between ice core temperature and snowfall proxies, North Atlantic oceanic and atmospheric processes, Arctic temperatures, and Indian summer monsoon intensity. Correlations between annual-scale oxygen isotopic ratios (δ18O) and tropical western Pacific and Indian Ocean sea surface temperatures are also demonstrated. Comparisons of climate records during the last millennium from ice cores acquired throughout the TP illustrate centennial-scale differences between monsoon and westerlies dominated regions. Among these records, Guliya shows the highest rate of warming since the end of the Little Ice Age, but δ18O data over the last millennium from TP ice cores support findings that elevation-dependent warming is most pronounced in the Himalaya. This, along with the decreasing precipitation rates in the Himalaya region, is having detrimental effects on the cryosphere. Although satellite monitoring of glaciers on the TP indicates changes in surface area, only a few have been directly monitored for mass balance and ablation from the surface. This type of ground-based study is essential to obtain a better understanding of the rate of ice shrinkage on the TP.

En los Andes peruanos, el calentamiento de la troposfera media, potenciado por el reciente fuerte El Niño, está destruyendo las señales climáticas preservadas en los campos de hielo y acelerando la retirada de los glaciares. En ninguna parte está mejor documentada la pérdida de los glaciares tropicales y es más importante que en los Andes del Perú. El registro más largo de retirada de glaciares proviene de un estudio de 44 años realizado en el casquete de hielo Quelccaya en el sur de los Andes, que prueba la pérdida de un archivo climático muy importante y la pérdida acelerada de un recurso hídrico que alimenta el río Amazonas y el lago Titicaca. En la Cordillera Blanca, los glaciares por debajo de los 5400 msnm sufren tanto un deshielo estacional como el movimiento del agua de deshielo a través de las capas superiores porosas. Debido a su gran altitud, el nevado Huascarán es uno de los pocos sitios tropicales donde aún se conserva una historia climática prácticamente inalterada, que se extiende hasta la última etapa glacial. Sin embargo, todos los glaciares de Cordillera Blanca documentados por INAIGEM (en prensa) estar en retroceso. Dadas las tasas actuales de calentamiento en los Andes tropicales, solo es cuestión de tiempo para que los registros climáticos del hielo del Huascarán también se pierdan. El retroceso de los glaciares a lo largo de los Andes peruanos está contribuyendo a las crisis emergentes de los recursos hídricos y los peligros ambientales tanto para las poblaciones urbanas como rurales. Aunque actualmente la descarga de la estación seca está aumentando, no se mantendrá así a largo plazo. La mayoría de la población del Perú vive en el desierto de la costa oeste, que depende de los ríos alimentados por los glaciares para la agricultura y los medios de subsistencia. El derretimiento de los glaciares también agrava los peligros geológicos en esta región propensa a terremotos, formando lagunas glaciares con represas de hielo o morrenas, lo que puede dar como resultado estallidos de lagunas e inundaciones y flujos de escombros. Comprender el impacto de esta aceleración de la pérdida de glaciares en los recursos hídricos futuros requiere informaciónsobre los cambios del pasado en el balance de masas de los glaciares de alta elevación.

High-elevation tropical glaciers provide records of past climate from which current changes can be assessed. Comparisons among three ice-core records from tropical mountains on opposite sides of the Pacific Ocean reveal how climatic events are linked through large-scale processes such as El Nino-Southern Oscillation. Two distinctive trans-Pacific events in the mid-fourteenth and late-eighteenth centuries are distinguished by elevated aerosol concentrations in cores from the Peruvian Andes and the Tibetan Himalaya. Today aerosol sources for these areas are enhanced by droughts accompanying El Ninos. In both locations, large-scale atmospheric circulation supports aerosol transport from likely source regions. Oxygen isotopic ratios from the ice cores are significantly linked with tropical Pacific sea-surface temperatures, especially in the NINO3.4 region. The arid periods in the fourteenth and eighteenth centuries reflect droughts that were possibly connected to strong and/or persistent El Nino conditions and Intertropical Convergence Zone migration. These 'black swans' are contemporaneous with climate-related population disruptions. Recent warming, particularly at high elevations, is posing a threat to tropical glaciers, many of which have been retreating at unprecedented rates over the last several thousand years. The diminishing ice in these alpine regions endangers water resources for populations in South Asia and South America.

Data collected between 1974 and 2016 from snow pits and core samples from two Peruvian ice fields demonstrate the effect of the recent warming over the tropical Andes, augmented by El Niño, on the preservation of the climate record. As the 0°C isotherm is approaching the summit of the Quelccaya ice cap in the Andes of southern Peru (5,670 meters above sea level (masl)), the distinctive seasonal δ 18 O oscillations in the fresh snow deposited within each thermal year are attenuated at depth due to melting and percolation through the firn. This has become increasingly pronounced over 43 years. In the Andes of northern Peru, the ice field on the col of Nevado Huascarán (6050 masl) has retained its seasonal δ 18 O variations at depth due to its higher elevation. During the 2015/2016 El Niño, snow on Quelccaya and Huascarán was isotopically (δ 18 O) enriched and the net sum of accumulation over the previous year (NSA) was below the mean for non–El Niño years, particularly on Quelccaya (up to 64% below the mean) which was more pronounced than the NSA decrease during the comparable 1982/1983 El Niño. Interannual large‐scale oceanic and middle to upper‐level atmospheric temperatures influence δ 18 O in precipitation on both ice fields, although the influences are variably affected by strong El Niño–Southern Oscillation events, especially on Quelccaya. The rate of ice wastage along Quelccaya's margin was dramatically higher during 2015/2016 compared with that of the previous 15 years, suggesting that warming from future El Niños may accelerate mass loss on Peruvian glaciers.

Annual net accumulation (A(n)) from the Bruce Plateau (BP) ice core retrieved from the Antarctic Peninsula exhibits a notable relationship with sea ice extent (SIE) in the Bellingshausen Sea. Over the satellite era, both BP A(n) and Bellingshausen SIE are influenced by large-scale climatic factors such as the Amundsen Sea Low, Southern Annular Mode, and Southern Oscillation. In addition to the direct response of BP A(n) to Bellingshausen SIE (e.g., more open water as a moisture source), these large-scale climate phenomena also link the BP and the Bellingshausen Sea indirectly such that they exhibit similar responses (e.g., northerly wind anomalies advect warm, moist air to the Antarctic Peninsula and neighboring Bellingshausen Sea, which reduces SIE and increases A(n)). Comparison with a time series of fast ice at South Orkney Islands reveals a relationship between BP A(n) and sea ice in the northern Weddell Sea that is relatively consistent over the twentieth century, except when it is modulated by atmospheric wave patterns described by the Trans-Polar Index. The trend of increasing accumulation on the Bruce Plateau since similar to 1970 agrees with other climate records and reconstructions in the region and suggests that the current rate of sea ice loss in the Bellingshausen Sea is unrivaled in the twentieth century.

A new ice core drilled in 2010 to bedrock from the Bruce Plateau (BP) on the Antarctic Peninsula (AP) provides a high temporal resolution record of environmental conditions in this region. The extremely high annual accumulation rate at this site facilitates analysis of the relationships between annual net accumulation A(n) on the BP and large-scale atmospheric oscillations. Over the last ~45 years, A(n) on the BP has been positively correlated with both the southern annular mode (SAM) and Southern Oscillation index (SOI). Extending this analysis back to 1900 reveals that these relationships are not temporally stable, and they exhibit major shifts in the late-1940s and the mid-1970s that are contemporaneous with phase changes in the Pacific decadal oscillation (PDO). These varying multidecadal characteristics of the A(n)-oscillation relationships are not apparent when only data from the post-1970s era are employed. Analysis of the longer ice core record reveals that the influence of the SAM on A(n) depends not only on the phase of the SAM and SOI but also on the phase of the PDO. When the SAM's influence on BP A(n) is reduced, such as under negative PDO conditions, BP A(n) is modulated by variability in the tropical and subtropical atmosphere through its impacts on the strength and position of the circumpolar westerlies in the AP region. These results demonstrate the importance of using longer-term ice core-derived proxy records to test conventional views of atmospheric circulation variability in the AP region.

The seasonality of accumulation in west central Greenland is investigated to determine whether a summer bias exists in a multi-century ice core recovered from Crawford Point (CP). Such a bias would negatively affect the ice core's potential for reconstructing the history of winter circulation patterns including the North Atlantic Oscillation. An automatic weather station (AWS) installed at the CP site in 1995 records sub-daily surface heights and affords a unique opportunity to assess the seasonal distribution of accumulation and test the performance of five gridded reanalysis datasets and a regional climate model. Simulated accumulation compares remarkably well with in situ measurements from both the AWS and CP ice core, demonstrating their potential to accurately represent accumulation in this region. Seasonal accumulation exhibits no summer maximum, indicating that any concurrent precipitation maximum is likely offset by melt and/or sublimation effects. The lack of a strong seasonal accumulation bias implies that the CP ice core is well suited for future investigations of the history of winter circulation patterns.