Abstract
The shrinking of Arctic-wide September sea ice extent is often cited as an indicator of modern climate change; however, the timing of seasonal sea ice retreat/advance and the length of the open-water period are often more relevant to stakeholders working at regional and local scales. Here we highlight changes in regional open-water periods at multiple warming thresholds. We show that, in the latest generation of models from the Coupled Model Intercomparison Project (CMIP6), the open-water period lengthens by 63 days on average with 2 °C of global warming above the 1850-1900 average, and by over 90 days in several Arctic seas. Nearly the entire Arctic, including the Transpolar Sea Route, has at least 3 months of open water per year with 3.5 °C warming, and at least 6 months with 5 °C warming. Model bias compared to satellite data suggests that even such dramatic projections may be conservative.
Highlights
The shrinking of Arctic-wide September sea ice extent is often cited as an indicator of modern climate change; the timing of seasonal sea ice retreat/advance and the length of the open-water period are often more relevant to stakeholders working at regional and local scales
Sea ice retreat day is defined as the last time sea ice concentration (SIC) falls below 15% before reaching its minimum annual value
Advance day is the first time after the minimum that SIC rises above 15%
Summary
The shrinking of Arctic-wide September sea ice extent is often cited as an indicator of modern climate change; the timing of seasonal sea ice retreat/advance and the length of the open-water period are often more relevant to stakeholders working at regional and local scales. A few studies have examined future projections of open-water periods using a previous intercomparison of global climate models (CMIP5), but only under a high-emissions scenario (RCP8.5) These simulations show that the lengthening of the projected pan-Arctic open-water period through 2200 is dominated by later ice advance[30]. The open-water period is assessed in terms of both time and global temperature anomalies (e.g., 1.5 and 2 °C) using output from CMIP6 models forced by low, medium and high emissions scenarios (SSP126, SSP245, and SSP585) This assessment aims to provide guidance and future projections of the open-water period (and the timing of sea ice retreat and advance) at multiple spatial scales and temperature thresholds. If and when we reach those thresholds depends on the choices that we make today
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