The IPCC Assessment Report 6 (AR6) Working Group I (WGI) had a strong focus on the Cryosphere, polar regions and glaciology. Chapter 9, “Ocean, Cryosphere and Sea Level Change” ensured a detailed analysis of the changes in polar and high mountain regions, reviewing systematically ocean heat and salinity, ocean circulation, sea ice, sea level, ice sheets, glaciers, permafrost and snow. It followed on from the IPCC AR6 Special Report on Oceans and the Cryosphere (2019). The lead and contributing author lists of these reports provide a veritable who’s-who in polar and cryospheric science, sea level rise and oceanography.
What is happening in the IPCC AR7? The chapter outlines and the author list have just been announced. The author list includes some very experienced IPCC authors, as coordinating lead authors, lead authors and review editors, and a series of authors new to the IPCC process.
For this report, the IPCC is taking a different tack. Working Group I, The Physical Science Basis, is divided into 10 chapters. Instead of a dedicated chapter on the Cryosphere, it is sprinkled throughout the chapter outlines. What does this mean for the Cryosphere and is it diminishing in importance in the IPCC?
Cryosphere in IPCC AR7 WGI
The structure of the IPCC AR7 report was decided at the IPCC Scoping Meeting in Kuala Lumpur in December 2024. The Scoping Meeting includes the Working Group co-chairs, and 240 experts (60 from each working group) nominated by their respective national focal points. As such, the Scoping Meeting includes important community involvement, and means that the structure of the IPCC reports reflects the community. Government representatives then tweak and sign off the intended report structure. This scoping meeting identified several cross-cutting topics for study in the IPCC AR7.
The cryosphere remains fundamentally important within the planned IPCC AR7 WGI, building on the IPCC Special Report on Oceans and Cryosphere (2019) and the 2021 IPCC AR6 Chapter 9: Ocean, Cryosphere and Sea Level Change. However, unlike the previous report, the chapters are less distinct thematically, and contain multiple cross-cutting themes and concepts. Disciplines are shown together, rather than separately. The Cryosphere and sea level rise remain emphasised throughout the IPCC, and academics may need to be better at reading the whole report, rather than simply referencing one chapter. As interdisciplinarity is increasingly acknowledged as fundamental to scientific progress and innovation, this is an interesting development that will foster a greater understanding of concepts adjacent to experts specialisms.
I think it is also important for the IPCC to reframe its reports for continued novelty and impact; a simple repeat of previous reports likely does not have the same transformative impact on both science and policy. The reports also need to be policy relevant – and reflect the changing nature of the geopolitical and scientific space.
IPCC AR7 structure
Chapter 1: Framing, methods and knowledge sources
Chapter 1, lead by experienced authors including Antarctic ice-core scientist Nerilie Abram, will provide the framing, narrative and context for AR7, summarise the key findings and gaps in AR6, identify knowledge sources, and explore methodologies, emerging topics, models and tools.
Chapter 2: Large-scale changes in the climate system and their causes
Chapter 2 will include an analysis of the natural and anthropogenic radiative forcing and Earth energy imbalance, indicators of climate change , observed changes across the Earth system and their recent and longer-term context, changes in modes of climate variability and monsoons, assessment of model-simulated past changes (including in the Cryosphere) and attribution of large-scale changes.
This is the chapter that I am involved with. The ‘observed changes’ will here include changes in the ocean and sea level and cryosphere.
Chapter 3: Changes in regional climate and extremes, and their causes
This chapter will study past changes, and include regions and spatial scales of analysis (including polar and mountain regions), disparities in regional information availability (including Indigenous People’s knowledge) and palaeoarchives. It will include advances and limitations in assessment of regional climate change and extremes, and emerging regional and local process understanding. It will include attribution of regional and local changes.
Chapter 4: Advances in process understanding of Earth system changes
This chapter will include biogechemical cycle processes and budgets, Earth-system energy budgets, Cryosphere processes (high mountain and polar), ocean processes (sea level rise and acidification), atmospheric processes, land-surface processes and land-atmosphere-ocean interactions, Earth-system feedbacks and model process evaluation. For the Quaternary scientists, it will include model process evaluation, including palaeoclimate constraints.
This chapter includes several notable cryospheric scientists, including experienced IPCC author Regine Hock, glaciologist William Colgan, arctic ecologist Susan Natali and mountain climatologist Nikolina Ban. With Cryosphere processes having its own bullet point, expect this to feature highly in this chapter.
Chapter 5: Scenarios and Projected future global temperatures
Chapter 5 will include a description of the scenarios, use and evaluation of models, Global Earth System and climate sensitivity metrics and properties, global temperature projections, global warming levels and timeframes, and carbon budgets.
Chapter 6: Global Projections of Earth System responses across timescales
This is another chapter where the cryosphere may be important. The first bullet highlights “Projected changes across the Earth System, its components and their ecosystems, including long-term changes in cryosphere and sea-level rise”.
This chapter is led by experienced IPCC author and climate scientist / Antarctic scientist Tamsin Edwards, with glaciologist Alfonso Fernandez, sea-ice expert Michael Sigmond and IPCC AR6 lead author and sea-level scientist Aimee Slangen also chapter authors. Gerhard Krinner, lead author of the IPCC AR6 chapter 9, is a review editor. Expect a strong focus on the Cryosphere in this chapter.
Chapter 7: Projections of regional climate and extremes
Chapter 7 assesses projected changes, linked with the assessment of past changes in Chapter 3. The projected regional and local changes will include sea level and the cryosphere.
Chapter 8: Abrupt changes, low-likelihood high impact events and critical thresholds, including tipping points, in the Earth system
Chapter 8 is a new feature of the IPCC WGI, with a specific chapter on tipping points. It includes several notable authors involved in the tipping points literature, including Tim Lenton and Robert Kopp, and polar / cryosphere scientists Ricarda Winkelmann, experienced IPCC author Cunde Xiao, and Shuting Yang. Expect the classic tipping point of the West Antarctic Ice Sheet and marine ice sheet instability to feature in this chapter.
Chapter 9: Earth system responses under pathways towards temperature stabilisation, including overshoot pathways
This chapter includes global and regional Earth system responses to pathways towards temperature stabilisation, including net zero. This will likely include glaciers and ice sheets, with glaciologist Henry Zekollari and polar biogeochemist Angela Gallego Sala on the author team. Interestingly, this chapter will also examine irreversibility and carbon removal.
Chapter 10: Climate information and services
This chapter will explore the usage of climate information, advances in climate information for climate services, methodologies to develop climate information, and case studies.
Summary
The Cryosphere, including sea ice, glaciers, ice sheets, permafrost, snow, and its impacts, including sea level rise and changes in water resources, remains fundamental to the assessment of climate change within the IPCC AR7. The observed past changes in this sphere are examined in Chapter 2, with a regional focus in Chapter 3. Processes of change will be examined in Chapter 4. Chapter 6, with a slew of glaciologists / polar scientists / sea level experts, will examine the projected changes in the Cryosphere. Chapter 8 will examine thresholds, abrupt change and tipping points in the Earth system, including ice sheets and glaciers, exploring perhaps the worst-case scenarios. Chapter 9, perhaps a more hopeful chapter, will examine the response of the cryosphere to projected climate change under net zero and temperature stabilisation.
Placing the Cryosphere alongside other Earth systems will enhance interdisciplinarity and emphasises the cross-cutting nature of the planned report. It is well supported by cryosphere and polar scientists in these key chapters, and promises to be an interesting report when it is published in a few years time.
As a naïve and new IPCC author, I am looking forward to learning more about the process in the coming few years.