Projections of an Ice-Free Arctic

Observed Arctic sea ice losses are a sentinel of anthropogenic climate change. These reductions are projected to continue with ongoing warming, ultimately leading to an ice-free Arctic (sea ice area <1 million km2). This transition from a white Arctic Ocean to a blue Arctic Ocean is visual example of anthropogenic climate change, with implications in the Arctic and globally. Based on climate model projections, the earliest ice-free conditions in the monthly September mean could occur as early as the late 2020 or the 2030s under all emission trajectories and are likely to occur by 2050. However, definition differences of what constitutes an ice-free Arctic can introduce differences in ice-free projections by a decade or more. For example, first daily September ice-free conditions are expected approximately 4 years earlier on average, with the possibility of preceding monthly metrics by over 10 years. Consistently ice-free September conditions (frequent occurrences of an ice-free Arctic) are anticipated by mid-century (by 2035–2067), and are reached under all CMIP6 emission scenarios. However, while ice-free conditions will occur under all emission scenarios, how often and for how long the Arctic could be ice free during the later half of the 21st century depends very strongly on future emission choices. Specifically, there is potential for ice-free conditions in May–January under a high-emission scenario, while under a low-emission scenario ice-free conditions will largely be limited to September, with occasional ice-free conditions in August and October.