- The sixth Assessment Report released by the Intergovernmental Panel on Climate Change (IPCC AR6) projects rapidly shrinking sea-ice cover for the Arctic in the summer months, with an ice-free Arctic already very likely toward the middle of the century.
- The underlying climate scenarios used for the AR6 are based on a combination of socioeconomic fundamentals and the greenhouse-gas emissions derived from them and are described by what are referred to as Shared Socioeconomic Pathways (SSPs).
- The climate simulations cover two historical periods (1975 – 1994 and 1995 – 2014). For the climate projections, the scenarios SSP1-2.6, SSP2-4.5 and SSP5-8.5 are evaluated for the periods 2021 – 2040, 2041 – 2060 and 2081 – 2100 respectively.
In addition to the global Coupled Model Intercomparison Project CMIP5 (Phase 5, 2010 – 2014) in connection with the Fifth Assessment Report released by the Intergovernmental Panel on Climate Change (IPCC AR5), the sea-ice projections from the Sixth Assessment Report (IPCC AR6) have now also been evaluated and visualised. The Coupled Model Intercomparison Project Phase 6 (CMIP6) is a major international initiative for climate research and provided an essential basis for the IPCC’s Sixth Assessment Report (IPCC AR6, 2021). It is intended to improve our grasp of the climate system and yield prognoses for future climatic developments. “CMIP6 is based on the successes of previous phases and offers an updated collection of climate model-based simulations, together with a new generation of climate models developed at research centres around the globe,” explains Dr Tido Semmler, a climate scientist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). Tido Semmler himself was involved with the AWI-CM and AWI-ESM climate models developed at the AWI. “The majority of the CMIP6 models project rapidly shrinking sea-ice cover for the Arctic, with an ice-free Arctic already very likely toward the middle of the century. This can only be avoided through a rapid and ambitious reduction in CO2 emissions worldwide,” says Tido Semmler, explaining the results.
The CMIP6 simulations encompass a broad range of climate variables and processes, including temperature, precipitation, sea ice, ocean circulation, cloud formation and much more. The models are used to draw comparisons between past, present and future climatic conditions, under both natural and anthropogenic influences.
The simulations are based on nine climate scenarios that combine socioeconomic base conditions and corresponding greenhouse-gas emission and concentration paths. These Shared Socioeconomic Pathways (SSPs) primarily consist of five scenarios: SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. The first part of the name (SSP1 etc.) refers to the socioeconomic development scenario; the second (1.9 etc.) to the increase in radiative forcing from the preindustrial era to the end of the century in W/m2. Whereas the scenario SSP5-8.5 comes close to the high-emissions scenarios from previous CMIPs, the more moderate SSP1-2.6 represents the goal of limiting global warming by the end of the century to roughly 1.5 degrees Celsius (mean value for all ensembles).
Description of the models / number of models
CMIP6 is a major model comparison study, bringing together 39 modelling groups from every corner of the world – a significant improvement on the roughly two dozen groups that took part in CMIP5.
The models vary in terms of their resolution, the processes and components depicted, and their origins from modelling centres around the globe. Applying multiple models is intended to improve our grasp of the uncertainties involved and the range of possible climatic developments.
Of the 39 CMIP6 models, it was possible to assess 34 in terms of their simulated sea-ice concentration. All model results were presented using their own specific modelling grid and analysed in terms of the ice extent / ice area. The time periods covered are 1975 – 1994 and 1995 – 2014. For the climate projections, the scenarios SSP1-2.6, SSP2-4.5 and SSP5-8.5 were analysed in the periods 2021 – 2040, 2041 – 2060 and 2081 – 2100.
CMIP6 sea-ice concentration maps (PNG format)
The data provided here offers insights into the sea-ice concentration according to simulations from CMIP6 (Fig. 1).
Each map provides information on the respective model, the time interval for the prognosis, and the sea-ice extent and area. In addition, the number of individual ensemble members included in the simulation is provided. The observed climatological border of the sea-ice extent (15%) for the period 1981 to 2010 (NSIDC) is shown in turquoise. This allows the modelled conditions to be directly, visually compared with the current sea-ice conditions. The 15% contour line for the modelled sea-ice extent is also shown on the maps (in red).
The models vary in both their complexity and their spatial resolution. Accordingly, their outcomes sometimes differ substantially. Nevertheless, all models predict an ice-free Arctic in September for the SSP5-8.5 scenario. The majority of the maps represent ensemble mean values for the respective SSP scenarios.
The new CMIP6 overview page on modeled sea ice concentration in the Arctic and Antarctic can be found here.
Contact
Dr. Tido Semmler (AWI, Met Éireann: Irish Meteorological Service)
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