Black carbon (BC) is a light-absorbing particle that warms the atmosphere–Earth system. The climate effects of BC are amplified in the Arctic, where its deposition on light surfaces decreases the albedo and causes earlier melt of snow and ice. Despite its suggested significant role in Arctic climate warming, there is little information on BC concentrations and deposition in the past. Here we present results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard glacier between 1700 and 2004. The inner part of a 125 m deep ice core from Holtedahlfonna glacier (79°8' N, 13°16' E, 1150 m a.s.l.) was melted, filtered through a quartz fibre filter and analysed for EC using a thermal–optical method. The EC values started to increase after 1850 and peaked around 1910, similar to ice core records from Greenland. Strikingly, the EC values again increase rapidly between 1970 and 2004 after a temporary low point around 1970, reaching unprecedented values in the 1990s. This rise is not seen in Greenland ice cores, and it seems to contradict atmospheric BC measurements indicating generally decreasing atmospheric BC concentrations since 1989 in the Arctic. For example, changes in scavenging efficiencies, post-depositional processes and differences in the vertical distribution of BC in the atmosphere are discussed for the differences between the Svalbard and Greenland ice core records, as well as the ice core and atmospheric measurements in Svalbard. In addition, the divergent BC trends between Greenland and Svalbard ice cores may be caused by differences in the analytical methods used, including the operational definitions of quantified particles, and detection efficiencies of different-sized BC particles. Regardless of the cause of the increasing EC values between 1970 and 2004, the results have significant implications for the past radiative energy balance at the coring site.

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 δ¹⁸O 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 δ¹⁸O variations at depth due to its higher elevation. During the 2015/2016 El Niño, snow on Quelccaya and Huascarán was isotopically (δ¹⁸O) 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 δ¹⁸O 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.

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 O ₂ in air bubbles (δ ¹⁸ O _atm ), along with annual layer counting and radiocarbon dating. We provide a robust chronology for water isotope records (δ ¹⁸ O _ice and d-excess) from three ice cores from the Guliya ice cap in the NWTP. The measurement of δ ¹⁸ O _atm , 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 (O ₂ ) by micro-organisms in the ice, which fractionates the δ ¹⁸ O of O ₂ 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 δ ¹⁸ O _ice are complex and temporally variable; however, Guliya δ ¹⁸ O _ice values since the mid-20th century are the highest since the beginning of the Holocene and have increased with regional air temperature.

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 (NH₄⁺) 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 NH₄⁺ 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 NH₄⁺ 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.