This special issue is prepared on the occasion of the 100th anniversary of the publication in Paris of Milutin Milankovic’s book "Théorie Mathématique des Phénomènes Thermiques Produits par la Radiation Solaire" (Mathematical Theory of Heat Phenomena Caused by Solar Radiation).
More precisely, it is related, but not limited, to the international conference held in Belgrade and online on 17–18 November 2020 "One Hundred Years of Milankovic’s Theory of Climate Changes: synergy of the achievements and challenges of the next century".

Volcanic eruptions can inject large amounts of material into the atmosphere, which impacts climate and societies on regional to global scales. The Volcanic Impacts on Climate and Society (VICS) working group, part of the Past Global Changes (PAGES) project, supports research focused on reconstructing the history of past volcanism, and its impact on the climate system and societies. This special issue provides authoritative statements on the state-of-the-art knowledge of historically and scientifically important eruptions from an interdisciplinary perspective and set an agenda for future research into links between volcanism, climate and society. These studies will provide updates on well-known events, as well as expanding the focus to include eruptions and time periods which have so far received less attention. Studies will integrate interdisciplinary evidence and explore the rich narrative circumstances and uncertainties unique to each event or period. As a collection, the special issue will highlight both the commonalities between eruptive events, as well as the variance in responses to different eruptions.

Personal documents, narrative sources, archival materials, and early instrumental observations play a vital role in reconstructing past climates and their historical consequences. However, evaluation of these “archives of societies” and their climate and weather information requires specialized training in local languages and history. The special issue aims to promote communication among researchers in historical climatology in different world regions by clarifying and comparing approaches. To this end, we invite global reviews and analyses of methods, sources, and results in historical climatology, as well as original research in regional and national historical climatology that explains its sources and methods for an international audience. We especially encourage contributions that facilitate international comparisons in different areas of historical climatology research, including (1) different national or regional source materials, such as the types of records available, their recording style, their temporal and spatial distribution, and the philosophical or cultural elements essential to their interpretation; (2) different methods of quantification and of calibration and verification of data in the archives of societies for the reconstruction of climate parameters, including the use of ice- and plant-phenological proxies and the indexing of qualitative descriptions; (3) the reporting of extreme weather and natural disasters in different national or regional contexts, including literary elements and political and religious biases in historical descriptions; and (4) methods of attributing societal impacts to climate variability in different national or regional contexts, including the availability and use of historical harvest, price, wage, and migration data. The broader goals of this SI include further collaboration among international researchers in historical climatology; dissemination of best practices in historical climatology; foundations for transcontinental climate reconstructions that incorporate the archives of societies; and more accurate cross-cultural comparative analyses of climate and weather impacts, adaptation, and resilience during past centuries.

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.

The Paleoclimate Modelling Intercomparison Project (PMIP) has been set up to provide a mechanism for coordinating paleoclimate modelling and model evaluation activities, to understand the mechanisms of climate change and the role of climate feedbacks in these changes. PMIP is now in its fourth phase: PMIP4. Five PMIP4 experiments have been proposed within the framework of the CMIP6 exercise. Other periods and sensitivity experiments are also planned to assess climate sensitivity, changes in hydrology, long-term trends and interannual to millennium variability. This special issue is devoted to the description of the design of the PMIP4 experiments, of data syntheses to which model results can be compared, and to papers analysing single or multi-model results from PMIP4 and CMIP6 experiments. Papers can either be submitted to GMD (model and simulation descriptions, data syntheses in support of the experimental design or of model-data comparisons) or CP (in-depth analyses, multi-model analyses, model-data comparisons).

The Pliocene Model Intercomparison Project (PlioMIP) Phase 2 is a strategic international climate modelling initiative that compares model predictions and uses climate models and geological proxy data together to better understand climate and environments of the late Pliocene. PlioMIP2 is also exploring the relevance of the Pliocene in the context of future climate change. We welcome submissions from registered participants that document the results of climate model simulations for the Pliocene using the PlioMIP2 protocols. These simulations will facilitate analyses of the dynamics of Pliocene climate and compare climate model results with each other. In addition comparisons of climate model results with proxy data will be presented.

Sea ice is a critical component of the Earth system in that it regulates heat and gas exchange between the atmosphere and polar oceans; it modulates Southern Ocean upper and lower overturning cells and global ocean circulation; it influences surface ocean stratification, ocean productivity, and nutrient and carbon cycling; and it interacts with ice sheets and ice shelves. As Antarctic sea-ice cover is predicted to decrease in the next decades, it is essential for our Earth system models to be able to simulate the effects of this waning. However, currently both modern and paleo data–model intercomparisons display large differences in sea-ice extent and trends. This affects the ability of these models to project the effects of sea-ice changes on the atmosphere, deep-ocean circulation, and nutrient cycling. Reconstructions of changes in sea-ice concentrations are pivotal to understand how Antarctic sea ice changed in the past and how it influenced these physical and biogeochemical processes. Most previous paleoclimate reconstructions of Southern Ocean sea ice have focused on the Last Glacial Maximum time slice (CLIMAP, MARGO projects) or the Holocene and last interglacial periods (PAGES working group Sea Ice Proxies (SIP)).

This special issue arises from the efforts of an international PAGES working group called Cycles of Sea-Ice Dynamics in the Earth System (C-SIDE), which aims to (a) reconstruct sea-ice conditions in the Southern Ocean over the last 130 000 years, (b) compare these reconstructions with complementary paleo-environmental data documenting changes in the Southern Ocean, and (c) use these data along with model simulations to improve our understanding of Earth system processes. The C-SIDE working group has chosen the last glacial–interglacial cycle (or last 130 000 years) as a focus because this timescale allows us to evaluate the role of sea ice on major climate transitions including glacial inception, when carbon was sequestered in the ocean, and deglaciation, when ocean carbon reserves were released to the atmosphere. The time frame also encompasses the penultimate interglacial when Antarctica was c. 2 °C warmer than today – a useful “process” analogue for future warming scenarios. At this time, the working group has held two workshops (October 2018 in Vancouver, Canada, and August/September 2019 in Sydney, Australia) to achieve these goals.

This special issue invites papers on the topics of (a) new sea-ice reconstructions in the Southern Ocean using new and established proxies of changes in sea ice; (b) regional compilations of changes in sea-ice distributions during the last glacial–interglacial cycle; (c) studies comparing (new and published) sea-ice records with complementary records of changes in circulation, temperature, and nutrient or carbon cycling; and (d) model analysis and model–data comparison papers that provide insights into the key processes linking Southern Ocean sea-ice changes with ice sheet, atmosphere, and ocean dynamics, as well as biogeochemical cycling in the ocean. We strongly encourage submissions that focus on at least one full glacial–interglacial cycle but encourage submissions from other time spans as well.

This special issue is prepared on the occasion of the 100th anniversary of the publication in Paris of Milutin Milankovic’s book "Théorie Mathématique des Phénomènes Thermiques Produits par la Radiation Solaire" (Mathematical Theory of Heat Phenomena Caused by Solar Radiation).
More precisely, it is related, but not limited, to the international conference held in Belgrade and online on 17–18 November 2020 "One Hundred Years of Milankovic’s Theory of Climate Changes: synergy of the achievements and challenges of the next century".

Sea ice is a critical component of the Earth system in that it regulates heat and gas exchange between the atmosphere and polar oceans; it modulates Southern Ocean upper and lower overturning cells and global ocean circulation; it influences surface ocean stratification, ocean productivity, and nutrient and carbon cycling; and it interacts with ice sheets and ice shelves. As Antarctic sea-ice cover is predicted to decrease in the next decades, it is essential for our Earth system models to be able to simulate the effects of this waning. However, currently both modern and paleo data–model intercomparisons display large differences in sea-ice extent and trends. This affects the ability of these models to project the effects of sea-ice changes on the atmosphere, deep-ocean circulation, and nutrient cycling. Reconstructions of changes in sea-ice concentrations are pivotal to understand how Antarctic sea ice changed in the past and how it influenced these physical and biogeochemical processes. Most previous paleoclimate reconstructions of Southern Ocean sea ice have focused on the Last Glacial Maximum time slice (CLIMAP, MARGO projects) or the Holocene and last interglacial periods (PAGES working group Sea Ice Proxies (SIP)).

This special issue arises from the efforts of an international PAGES working group called Cycles of Sea-Ice Dynamics in the Earth System (C-SIDE), which aims to (a) reconstruct sea-ice conditions in the Southern Ocean over the last 130 000 years, (b) compare these reconstructions with complementary paleo-environmental data documenting changes in the Southern Ocean, and (c) use these data along with model simulations to improve our understanding of Earth system processes. The C-SIDE working group has chosen the last glacial–interglacial cycle (or last 130 000 years) as a focus because this timescale allows us to evaluate the role of sea ice on major climate transitions including glacial inception, when carbon was sequestered in the ocean, and deglaciation, when ocean carbon reserves were released to the atmosphere. The time frame also encompasses the penultimate interglacial when Antarctica was c. 2 °C warmer than today – a useful “process” analogue for future warming scenarios. At this time, the working group has held two workshops (October 2018 in Vancouver, Canada, and August/September 2019 in Sydney, Australia) to achieve these goals.

This special issue invites papers on the topics of (a) new sea-ice reconstructions in the Southern Ocean using new and established proxies of changes in sea ice; (b) regional compilations of changes in sea-ice distributions during the last glacial–interglacial cycle; (c) studies comparing (new and published) sea-ice records with complementary records of changes in circulation, temperature, and nutrient or carbon cycling; and (d) model analysis and model–data comparison papers that provide insights into the key processes linking Southern Ocean sea-ice changes with ice sheet, atmosphere, and ocean dynamics, as well as biogeochemical cycling in the ocean. We strongly encourage submissions that focus on at least one full glacial–interglacial cycle but encourage submissions from other time spans as well.

Personal documents, narrative sources, archival materials, and early instrumental observations play a vital role in reconstructing past climates and their historical consequences. However, evaluation of these “archives of societies” and their climate and weather information requires specialized training in local languages and history. The special issue aims to promote communication among researchers in historical climatology in different world regions by clarifying and comparing approaches. To this end, we invite global reviews and analyses of methods, sources, and results in historical climatology, as well as original research in regional and national historical climatology that explains its sources and methods for an international audience. We especially encourage contributions that facilitate international comparisons in different areas of historical climatology research, including (1) different national or regional source materials, such as the types of records available, their recording style, their temporal and spatial distribution, and the philosophical or cultural elements essential to their interpretation; (2) different methods of quantification and of calibration and verification of data in the archives of societies for the reconstruction of climate parameters, including the use of ice- and plant-phenological proxies and the indexing of qualitative descriptions; (3) the reporting of extreme weather and natural disasters in different national or regional contexts, including literary elements and political and religious biases in historical descriptions; and (4) methods of attributing societal impacts to climate variability in different national or regional contexts, including the availability and use of historical harvest, price, wage, and migration data. The broader goals of this SI include further collaboration among international researchers in historical climatology; dissemination of best practices in historical climatology; foundations for transcontinental climate reconstructions that incorporate the archives of societies; and more accurate cross-cultural comparative analyses of climate and weather impacts, adaptation, and resilience during past centuries.

Volcanic eruptions can inject large amounts of material into the atmosphere, which impacts climate and societies on regional to global scales. The Volcanic Impacts on Climate and Society (VICS) working group, part of the Past Global Changes (PAGES) project, supports research focused on reconstructing the history of past volcanism, and its impact on the climate system and societies. This special issue provides authoritative statements on the state-of-the-art knowledge of historically and scientifically important eruptions from an interdisciplinary perspective and set an agenda for future research into links between volcanism, climate and society. These studies will provide updates on well-known events, as well as expanding the focus to include eruptions and time periods which have so far received less attention. Studies will integrate interdisciplinary evidence and explore the rich narrative circumstances and uncertainties unique to each event or period. As a collection, the special issue will highlight both the commonalities between eruptive events, as well as the variance in responses to different eruptions.

The Paleoclimate Modelling Intercomparison Project (PMIP) has been set up to provide a mechanism for coordinating paleoclimate modelling and model evaluation activities, to understand the mechanisms of climate change and the role of climate feedbacks in these changes. PMIP is now in its fourth phase: PMIP4. Five PMIP4 experiments have been proposed within the framework of the CMIP6 exercise. Other periods and sensitivity experiments are also planned to assess climate sensitivity, changes in hydrology, long-term trends and interannual to millennium variability. This special issue is devoted to the description of the design of the PMIP4 experiments, of data syntheses to which model results can be compared, and to papers analysing single or multi-model results from PMIP4 and CMIP6 experiments. Papers can either be submitted to GMD (model and simulation descriptions, data syntheses in support of the experimental design or of model-data comparisons) or CP (in-depth analyses, multi-model analyses, model-data comparisons).

The Pliocene Model Intercomparison Project (PlioMIP) Phase 2 is a strategic international climate modelling initiative that compares model predictions and uses climate models and geological proxy data together to better understand climate and environments of the late Pliocene. PlioMIP2 is also exploring the relevance of the Pliocene in the context of future climate change. We welcome submissions from registered participants that document the results of climate model simulations for the Pliocene using the PlioMIP2 protocols. These simulations will facilitate analyses of the dynamics of Pliocene climate and compare climate model results with each other. In addition comparisons of climate model results with proxy data will be presented.

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.