Permafrost is a widespread phenomenon in the cold regions of the globe and is clearly under-represented in global monitoring networks. Studies of permafrost dynamics are typically conducted through boreholes, which are invasive, expensive, and rarely representative at the field level. Geophysical techniques such as electrical, electromagnetic, and seismic methods have demonstrated their potential as useful non-invasive tools for detecting, mapping, and characterizing permafrost with a spatial and temporal resolution which cannot be achieved using only borehole data. Moreover geophysical surveys are flexible and can be easily adapted to different field conditions and investigation targets. Today, electrical methods such as electrical resistivity tomography (ERT) have been established as standard techniques to gain a general understanding of the subsurface structure at permafrost sites. In addition, there is a growing interest in the development of emerging technologies such as induced polarization methods and environmental seismology as well as joint inversion approaches of multiple datasets to gain a better interpretation of geophysical signatures at permafrost sites. Given their high sensitivity to changes in the ice and water content of the subsurface, repeated surveys, as well as continuous monitoring of geophysical properties, have become popular for monitoring permafrost degradation in both polar and mountain permafrost environments. A dedicated action group of the International Permafrost Association (IPA) has recently been formed to advance an international database for electrical survey data on permafrost (Towards an International Database of Geoelectrical Surveys on Permafrost, IDGSP).

This special issue aims for an overview of current challenges and recent advances in detecting, characterizing, and monitoring the geophysical properties of frozen ground, including advances in survey design and monitoring set‐up, processing and inversion of collected time series, laboratory experiments, and quantification of temporal changes in ground ice content. We welcome applied and theoretical contributions based on all relevant geophysical techniques from polar and mountain permafrost environments as well as laboratory investigations.

The loss of mass from glaciers, ice caps, and polar ice sheets has accelerated over the last 3 decades as a result of climate change. This has made land ice the major contributor to sea level rise and the main cause of its acceleration. However, the evolution of the land-based cryosphere over the course of the 21st century and beyond adds considerable uncertainties to sea level rise projections, particularly if instability mechanisms are triggered, leading to rapid retreat of marine basins in Antarctica. Critical knowledge gaps pose challenges for predicting the land ice response to the evolution of climate and the resulting impact on sea level, from cryospheric process understanding, ice sheet and glacier modelling, and coupling with the atmosphere and ocean to bridging the gap with sea level and coastal-impact sciences. This special issue includes contributions related to the following:

• Earth observations that help to constrain glacier and ice sheet surface conditions, dynamics, or mass loss;
• theoretical or numerical modelling of cryospheric processes or coupling with the ocean and atmosphere;
• standalone or coupled projections of ice surface mass balance;
• Arctic and Antarctic ocean conditions promoting and/or responding to ice sheet loss;
• glacier or ice sheet dynamics and mass balance;
• approaches to analysing multi-model ensembles or computing global and regional sea level rise projections;
• coastal impacts of sea level rise and climate change, adaptation needs, and related climate services.

High-latitude regions are experiencing amplified anthropogenic global warming. Cryospheric changes (e.g. permafrost thaw, snow and ice accumulation, and melt) are strongly coupled with the hydrologic cycle and severely impact the amount and seasonality of groundwater recharge and streamflow generation and associated biogeochemical cycling. These widespread changes, in turn, affect ecological and human systems, with impacts evident even in the ocean. This special issue aims to foster knowledge exchange across communities to gain a better understanding of coupled processes between the cryosphere, hydrology, ecosystems, and humans. We welcome all contributions on topics related to cold-region hydrology with a focus on inter- and transdisciplinary approaches and particularly invite contributions targeting the following aspects:

• climate-change-induced cryospheric alterations and impacts on the water cycle in northern environments, e.g. changes in the snowpack, glacier recession, permafrost thaw, stream discharge, lake size, and wildfires;
• interdisciplinary research that furthers our understanding of the nexus between hydrological, biogeochemical, and ecosystem processes in cold-region environments;
• the impacts of current (e.g. mining, logging, dam building) and past (e.g. peatland drainage/restoration) land-use changes in high-latitude regions;
• transdisciplinary research, including knowledge of Indigenous communities and other interested parties, ideally aimed at sustainable co-development of climate change adaptation and mitigation strategies;
• studies providing open tools for the development and testing of transposable models in cold-region environments;
• studies providing information on or presenting new tools for the improvement and standardization of measurement techniques and network design in northern regions.

The glacial–interglacial cyclicity of the climate system varied in the past, most notably during the transition from a 40 ka to a 100 ka world in the mid-Pleistocene. Gases trapped in Antarctic ice are the most direct access available to investigate the composition of the paleo-atmosphere of that age and processes related to climate variability. The International Partnerships in Ice Core Sciences (IPICS) Oldest Ice endeavour aims at obtaining an undisturbed ice-core record older than 1 Ma. In addition to ice cores, time slices of paleo-records, available, for example, in Antarctic blue-ice fields, provide further valuable information, which complements continuous time series based on ice cores. This special issue will assemble contributions dedicated to the preparatory phase of this global effort to obtain ice samples and time series older than 700 000 years. This includes a consideration of glaciogical and geophysical settings which allow the presence of old ice, results from pre-site surveys and modelling studies, aspects of ice-core and other sampling techniques and analyses, and requirements for drilling and core handling.

Two closely coordinated groups (one from the USA and the other from Europe) are revisiting the Camp Century sub-ice sediment and the silty ice zone just above it using a wide variety of analytical techniques to make inferences about ice sheet behaviour, palaeo-climate, and palaeo-ecology as well as sediment transport and sourcing. The paper that kicked this off was in Proceedings of the National Academy of Sciences (PNAS) 2 years ago: "A multi-million-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century" (Christ et al., 2021).

Talking among the 20+ lead investigators, we decided that the papers coming out of multiple, coordinated investigations of this historic (and still unique) ice core would be very useful to the broader community if they could be gathered into a special issue. Having these papers together would increase their impact and accessibility. Because of the wide variety of investigations being conducted on the core materials, a combined special issue including papers from both The Cryosphere and Climate of the Past will generate the most contributions and the largest readership.

Reference:

Christ, A. J., Bieman, P. R., Schaefer, J. M., Dahl-Jensen, D., Steffensen, J. P, Corbett, L. B., Peteet, D. M., Thomas, E. K., Steig, E. J., Rittenour, T. M., Tison, J.-L., Blard, P.-H., Perdrial, N., Dethier, D. P., Lini, A., Hidy, A. J., Caffee, M. W., and Southon, J.: A multi-million-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century, P. Natl. Acad. Sci. USA, 118, e2021442118, https://doi.org/10.1073/pnas.2021442118, 2021.

Permafrost is a widespread phenomenon in the cold regions of the globe and is clearly under-represented in global monitoring networks. Studies of permafrost dynamics are typically conducted through boreholes, which are invasive, expensive, and rarely representative at the field level. Geophysical techniques such as electrical, electromagnetic, and seismic methods have demonstrated their potential as useful non-invasive tools for detecting, mapping, and characterizing permafrost with a spatial and temporal resolution which cannot be achieved using only borehole data. Moreover geophysical surveys are flexible and can be easily adapted to different field conditions and investigation targets. Today, electrical methods such as electrical resistivity tomography (ERT) have been established as standard techniques to gain a general understanding of the subsurface structure at permafrost sites. In addition, there is a growing interest in the development of emerging technologies such as induced polarization methods and environmental seismology as well as joint inversion approaches of multiple datasets to gain a better interpretation of geophysical signatures at permafrost sites. Given their high sensitivity to changes in the ice and water content of the subsurface, repeated surveys, as well as continuous monitoring of geophysical properties, have become popular for monitoring permafrost degradation in both polar and mountain permafrost environments. A dedicated action group of the International Permafrost Association (IPA) has recently been formed to advance an international database for electrical survey data on permafrost (Towards an International Database of Geoelectrical Surveys on Permafrost, IDGSP).

This special issue aims for an overview of current challenges and recent advances in detecting, characterizing, and monitoring the geophysical properties of frozen ground, including advances in survey design and monitoring set‐up, processing and inversion of collected time series, laboratory experiments, and quantification of temporal changes in ground ice content. We welcome applied and theoretical contributions based on all relevant geophysical techniques from polar and mountain permafrost environments as well as laboratory investigations.

High-latitude regions are experiencing amplified anthropogenic global warming. Cryospheric changes (e.g. permafrost thaw, snow and ice accumulation, and melt) are strongly coupled with the hydrologic cycle and severely impact the amount and seasonality of groundwater recharge and streamflow generation and associated biogeochemical cycling. These widespread changes, in turn, affect ecological and human systems, with impacts evident even in the ocean. This special issue aims to foster knowledge exchange across communities to gain a better understanding of coupled processes between the cryosphere, hydrology, ecosystems, and humans. We welcome all contributions on topics related to cold-region hydrology with a focus on inter- and transdisciplinary approaches and particularly invite contributions targeting the following aspects:

• climate-change-induced cryospheric alterations and impacts on the water cycle in northern environments, e.g. changes in the snowpack, glacier recession, permafrost thaw, stream discharge, lake size, and wildfires;
• interdisciplinary research that furthers our understanding of the nexus between hydrological, biogeochemical, and ecosystem processes in cold-region environments;
• the impacts of current (e.g. mining, logging, dam building) and past (e.g. peatland drainage/restoration) land-use changes in high-latitude regions;
• transdisciplinary research, including knowledge of Indigenous communities and other interested parties, ideally aimed at sustainable co-development of climate change adaptation and mitigation strategies;
• studies providing open tools for the development and testing of transposable models in cold-region environments;
• studies providing information on or presenting new tools for the improvement and standardization of measurement techniques and network design in northern regions.

Two closely coordinated groups (one from the USA and the other from Europe) are revisiting the Camp Century sub-ice sediment and the silty ice zone just above it using a wide variety of analytical techniques to make inferences about ice sheet behaviour, palaeo-climate, and palaeo-ecology as well as sediment transport and sourcing. The paper that kicked this off was in Proceedings of the National Academy of Sciences (PNAS) 2 years ago: "A multi-million-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century" (Christ et al., 2021).

Talking among the 20+ lead investigators, we decided that the papers coming out of multiple, coordinated investigations of this historic (and still unique) ice core would be very useful to the broader community if they could be gathered into a special issue. Having these papers together would increase their impact and accessibility. Because of the wide variety of investigations being conducted on the core materials, a combined special issue including papers from both The Cryosphere and Climate of the Past will generate the most contributions and the largest readership.

Reference:

Christ, A. J., Bieman, P. R., Schaefer, J. M., Dahl-Jensen, D., Steffensen, J. P, Corbett, L. B., Peteet, D. M., Thomas, E. K., Steig, E. J., Rittenour, T. M., Tison, J.-L., Blard, P.-H., Perdrial, N., Dethier, D. P., Lini, A., Hidy, A. J., Caffee, M. W., and Southon, J.: A multi-million-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century, P. Natl. Acad. Sci. USA, 118, e2021442118, https://doi.org/10.1073/pnas.2021442118, 2021.

The loss of mass from glaciers, ice caps, and polar ice sheets has accelerated over the last 3 decades as a result of climate change. This has made land ice the major contributor to sea level rise and the main cause of its acceleration. However, the evolution of the land-based cryosphere over the course of the 21st century and beyond adds considerable uncertainties to sea level rise projections, particularly if instability mechanisms are triggered, leading to rapid retreat of marine basins in Antarctica. Critical knowledge gaps pose challenges for predicting the land ice response to the evolution of climate and the resulting impact on sea level, from cryospheric process understanding, ice sheet and glacier modelling, and coupling with the atmosphere and ocean to bridging the gap with sea level and coastal-impact sciences. This special issue includes contributions related to the following:

• Earth observations that help to constrain glacier and ice sheet surface conditions, dynamics, or mass loss;
• theoretical or numerical modelling of cryospheric processes or coupling with the ocean and atmosphere;
• standalone or coupled projections of ice surface mass balance;
• Arctic and Antarctic ocean conditions promoting and/or responding to ice sheet loss;
• glacier or ice sheet dynamics and mass balance;
• approaches to analysing multi-model ensembles or computing global and regional sea level rise projections;
• coastal impacts of sea level rise and climate change, adaptation needs, and related climate services.

The glacial–interglacial cyclicity of the climate system varied in the past, most notably during the transition from a 40 ka to a 100 ka world in the mid-Pleistocene. Gases trapped in Antarctic ice are the most direct access available to investigate the composition of the paleo-atmosphere of that age and processes related to climate variability. The International Partnerships in Ice Core Sciences (IPICS) Oldest Ice endeavour aims at obtaining an undisturbed ice-core record older than 1 Ma. In addition to ice cores, time slices of paleo-records, available, for example, in Antarctic blue-ice fields, provide further valuable information, which complements continuous time series based on ice cores. This special issue will assemble contributions dedicated to the preparatory phase of this global effort to obtain ice samples and time series older than 700 000 years. This includes a consideration of glaciogical and geophysical settings which allow the presence of old ice, results from pre-site surveys and modelling studies, aspects of ice-core and other sampling techniques and analyses, and requirements for drilling and core handling.