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1. The impacts of warming on rapidly retreating high-altitude, low-latitude glaciers and ice core-derived climate records

   Thompson, L. G. ; Davis, M. E. ; Mosley-Thompson, E. ; Porter, S. E. ; Corrales, G. V. ; Shuman, C. A. ; Tucker, C. J. ( January 2021 , Global and planetary change)

   null (Ed.)

   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 (δ18O) measured in ice cores drilled from several glaciers in these regions reveal that the records from elevations below ~6000 m above sea level have been substantially modified by seasonal melting and the movement of meltwater through porous upper firn layers. Fortunately, δ18O 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. 

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2. The impacts of warming on rapidly retreating high-altitude, low-latitude glaciers and ice core-derived climate records

   https://doi.org/https://doi.org/10.1016/j.gloplacha.2021.103538  

   Thompson, L. G. ; Davis, M. E. ; Mosley-Thompson, E. ; Porter, S. E. ; Corrales, G. V. ; Shuman, C. A. ; Tucker, C. J. ( January 2021 , Global and planetary change)

   null (Ed.)

   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 (δ18O) measured in ice cores drilled from several glaciers in these regions reveal that the records from elevations below ~6000 m above sea level have been substantially modified by seasonal melting and the movement of meltwater through porous upper firn layers. Fortunately, δ18O 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. 

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3. Expedition 363 Scientific Prospectus: Western Pacific Warm Pool

   https://doi.org/10.14379/iodp.sp.363.2016  

   Rosenthal, Y. ; Holbourn, A. ; Kulhanek, D.K. ( February 2016 , Scientific prospectus)

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   Expedition 363 seeks to document the regional expression of climate variability (e.g., temperature, precipitation, and productivity) in the Western Pacific Warm Pool (WPWP) as it relates to global and regional climate change from the middle Miocene to Late Pleistocene on millennial, orbital, and secular timescales. The WPWP is the largest reservoir of warm surface water on Earth and thus is a major source of heat and moisture to the atmosphere. Variations in sea-surface temperature and the extent of the WPWP influence the location and strength of convection and thus impact oceanic and atmospheric circulation, heat transport, and tropical hydrology. Given its documented importance for modern climatology, changes in the WPWP are assumed to have also played a key role in the past. The proposed drill sites are strategically located at the heart of the WPWP (northern Papua New Guinea and south of Guam) and around its western edge (western margin of Australia to the south and southern Philippine Islands to the north) to capture the most salient features of the WPWP. Combining marginal and open ocean sites will allow us to study these time intervals at different temporal resolutions. The coring program prioritizes seven primary sites and nine alternate sites in 880–3427 m water depth. This depth range will allow the reconstruction of intermediate and deepwater properties through time. 

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4. Modulation of late Pleistocene ENSO strength by the tropical Pacific thermocline

   https://doi.org/10.1038/s41467-020-19161-6  

   Rustic, Gerald T. ; Polissar, Pratigya J. ; Ravelo, Ana Christina ; White, Sarah M. ( October 2020 , Nature Communications)

   The El Niño Southern Oscillation (ENSO) is highly dependent on coupled atmosphere-ocean interactions and feedbacks, suggesting a tight relationship between ENSO strength and background climate conditions. However, the extent to which background climate state determines ENSO behavior remains in question. Here we present reconstructions of total variability and El Niño amplitude from individual foraminifera distributions at discrete time intervals over the past ~285,000 years across varying atmospheric CO₂levels, global ice volume and sea level, and orbital insolation forcing. Our results show a strong correlation between eastern tropical Pacific Ocean mixed-layer thickness and both El Niño amplitude and central Pacific variability. This ENSO-thermocline relationship implicates upwelling feedbacks as the major factor controlling ENSO strength on millennial time scales. The primacy of the upwelling feedback in shaping ENSO behavior across many different background states suggests accurate quantification and modeling of this feedback is essential for predicting ENSO’s behavior under future climate conditions.

    

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5. A probabilistic framework for quantifying the role of anthropogenic climate change in marine-terminating glacier retreats

   https://doi.org/10.5194/tc-16-2725-2022  

   Christian, John Erich ; Robel, Alexander A. ; Catania, Ginny ( January 2022 , The Cryosphere)

   Abstract. Many marine-terminating outlet glaciers have retreated rapidly in recent decades, but these changes have not been formally attributed to anthropogenic climate change. A key challenge for such an attribution assessment is that if glacier termini are sufficiently perturbed from bathymetric highs, ice-dynamic feedbacks can cause rapid retreat even without further climate forcing. In the presence of internal climate variability, attribution thus depends on understanding whether (or how frequently) these rapid retreats could be triggered by climatic noise alone. Our simulations with idealized glaciers show that in a noisy climate, rapid retreat is a stochastic phenomenon. We therefore propose a probabilistic approach to attribution and present a framework for analysis that uses ensembles of many simulations with independent realizations of random climate variability. Synthetic experiments show that century-scale climate trends substantially increase the likelihood of rapid glacier retreat. This effect depends on the timescales over which ice dynamics integrate forcing. For a population of synthetic glaciers with different topographies, we find that external trends increase the number of large retreats triggered within the population, offering a metric for regional attribution. Our analyses suggest that formal attribution studies are tractable and should be further pursued to clarify the human role in recent ice-sheet change. We emphasize that early-industrial-era constraints on glacier and climate state are likely to be crucial for such studies. 

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