Two equally probable, but vastly different transitions, to a seasonally ice-free Arctic

Implications for global warming communication

Sandrine Trotechaud1, Bruno Tremblay1,2
McGill University, 2Columbia University Lamont-Doherty Earth Observatory


The decline in the minimum sea ice extent (Min SIE) has been the center of attention since a few years. Global climate models project a seasonally ice-free Arctic within the next two/three decades. Of the 40 ensemble members (EM) from the CESM-LE model, two are of interest:

Both EMs however lead to a seasonally ice-free Arctic.

Fig. 1 - Min SIE and 5-year running mean for EM 13 (blue), 27 (green) and observations (red) from (Fetterer et al., 2017). Key periods are identified by shaded areas.

A recovery in the Min SIE can have an impact on the communication of global warming, because it could cast doubts in people's mind about the existence of climate change. Therefore, the objective of the project is to understand the mechanisms responsible for such trends in the Min SIE.



A rapid decline (RD) is defined as being steeper than -0.3 million km 2 per year in 5-year running mean. Gradual declines (GD) identified are less steep, but still important in the study.

Method (continued)

Spatial Domain

The spatial domain of this study consists of the Arctic Ocean. It includes the Barents Sea Opening (BSO), the Fram Strait and the Bering Strait. The continental shelves, characterized by depths shallower than 425 meters, are shown on the figure below as grey shaded area.

Fig. 2 - Spatial domain (Auclair and Tremblay, 2018).

Ocean heat transport defined through a gate:



Results : EM 27

Fig. 3 - Gradual and rapid decline.

The EM 27 has two key periods identified: a gradual decline from 1999 (black) to 2016 (cyan) and a rapid decline from 2016 to 2022 (green).

Results : EM 27 (continued)

Fig. 4 - OHT and Min SIE.

According to a 20-year sliding window correlation of the anomalies:

Results: EM 13

Fig. 5 - First rapid decline.
Fig. 6 - Recovery period.

Results: EM 13 (continued)

Fig. 7 - Second rapid decline.

The EM 13 has three key periods identified: a gradual decline from 2000 (black) to 2014 (green), a recovery period from 2014 to 2020 (pink) followed by a rapid decline from 2020 to 2029 (cyan).

Fig. 8 - OHT and Min SIE.

Shown by the correlation of the anomalies:

Fig. 9 - SW (from May to September), LW (from September to May) heat fluxes and Min SIE.

The SW and LW heat fluxes are significantly anti-correlated with the Min SIE (resp. r=-0.95 and r=-0.75). The LW heat flux undergo a considerable increase during the RD.


From the results and with further investigation, we can note that:

Multiple scenarios are plausible for the future trend in the Min SIE due to great climate variability. A considerable recovery in the Min SIE is possible even at a nearly ice-free Arctic condition through internal variability. However, as we saw in the case of EM 13, it is not sustainable and the EM still projects a seasonal ice-free cover within a few years of EM 27.

Hence, recoveries in the Arctic sea ice cover are possible due to climate variability, even with the presence of climate change.

Sa/ph/m/ari logo