Constraining the Date of a Seasonally Ice-Free Arctic Using a Simple Model

• Published in: Geophysical Research Letters
• Main Authors: Bonan, David B., Schneider, Tapio, Eisenman, Ian, Wills, Robert C. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2021
• Subjects: Arctic; Sea ice
• Online Access: https://authors.library.caltech.edu/109164/; https://authors.library.caltech.edu/109164/7/2021GL094309.pdf; https://authors.library.caltech.edu/109164/1/essoar.10507054.1.pdf; https://authors.library.caltech.edu/109164/4/2021gl094309-sup-0001-supporting%20information%20si-s01.pdf; https://resolver.caltech.edu/CaltechAUTHORS:20210518-081155344

State-of-the-art climate models simulate a large spread in the projected decline of Arctic sea-ice area (SIA) over the 21st century. Here we diagnose causes of this intermodel spread using a simple model that approximates future SIA based on present SIA and the sensitivity of SIA to Arctic temperatures. This model accounts for 70%–95% of the intermodel variance, with the majority of the spread arising from present-day biases. The remaining spread arises from intermodel differences in Arctic warming, with some contribution from differences in the local sea-ice sensitivity. Using observations to constrain the projections moves the probability of an ice-free Arctic forward by 10–35 years when compared to unconstrained projections. Under a high-emissions scenario, an ice-free Arctic will likely (urn:x-wiley:00948276:media:grl62946:grl62946-math-000166% probability) occur between 2036 and 2056 in September and between 2050 and 2068 from July to October. Under a medium-emissions scenario, the “likely” date occurs between 2040 and 2062 in September and much later in the 21st century from July to October.