Abstract
Arctic sea ice has been retreating at an accelerating pace over the past decades. Model projections show that the Arctic Ocean could be almost ice free in summer by the middle of this century. However, the uncertainties related to these projections are relatively large. Here we use 33 global climate models from the Coupled Model Intercomparison Project 6 (CMIP6) and select models that best capture the observed Arctic sea-ice area and volume and northward ocean heat transport to refine model projections of Arctic sea ice. This model selection leads to lower Arctic sea-ice area and volume relative to the multi-model mean without model selection and summer ice-free conditions could occur as early as around 2035. These results highlight a potential underestimation of future Arctic sea-ice loss when including all CMIP6 models.
Highlights
Arctic sea ice has been retreating at an accelerating pace over the past decades
Averaged over 33 Coupled Model Intercomparison Project 6 (CMIP6) models, the multi-model mean March Arctic sea-ice area and volume are reduced by 45% and 78%, respectively, in 2096–2100, compared to 2015–2019, in the high-emission scenario (Fig. 1a and Supplementary Fig. 1a)
Note that first ice-free conditions are reached about 10 years earlier in a previous CMIP6 study[24] that did not include two models that have a high mean state bias and used only the first member of each model
Summary
Arctic sea ice has been retreating at an accelerating pace over the past decades. Model projections show that the Arctic Ocean could be almost ice free in summer by the middle of this century. The observed sensitivity of sea-ice changes to cumulative greenhouse gas emissions has been used to provide an estimate of the future Arctic sea-ice area[11] This simple linear extrapolation neglects non-linearities in the climate system and oceanice-atmosphere interactions and feedbacks[12,13,14], resulting in large short- and long-term deviations from the ongoing negative trend in sea-ice area and volume[15,16,17,18]. Global climate models coupling the atmosphere, ocean and sea ice are well suited to make such projections[21,22,23,24] The inclusion of these models in the different Coupled Model Intercomparison Project (CMIP) phases[25,26,27] allows for estimates of Arctic sea-ice area and volume projections in the decades to centuries. We find that summer ice-free Arctic conditions could occur as early as around 2035 in the selection case, compared to 2061 in the no-selection case
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