Increase of the Antarctic Sea Ice Extent is highly significant only in the Ross Sea

Naiming Yuan,Minghu Ding,Josef Ludescher,Armin Bunde

doi:10.1038/srep41096

Abstract

In the context of global warming, the question of why Antarctic sea ice extent (SIE) has increased is one of the most fundamental unsolved mysteries. Although many mechanisms have been proposed, it is still unclear whether the increasing trend is anthropogenically originated or only caused by internal natural variability. In this study, we employ a new method where the underlying natural persistence in the Antarctic SIE can be correctly accounted for. We find that the Antarctic SIE is not simply short-term persistent as assumed in the standard significance analysis, but actually characterized by a combination of both short- and long-term persistence. By generating surrogate data with the same persistence properties, the SIE trends over Antarctica (as well as five sub-regions) are evaluated using Monte-Carlo simulations. It is found that the SIE trends over most sub-regions of Antarctica are not statistically significant. Only the SIE over Ross Sea has experienced a highly significant increasing trend (p = 0.008) which cannot be explained by natural variability. Influenced by the positive SIE trend over Ross Sea, the SIE over the entire Antarctica also increased over the past decades, but the trend is only at the edge of being significant (p = 0.034).

Highlights

Polar sea ice, as an important component of the climate system, can affect the earth system in many ways
In the previous calculations of the trend significance, it has been assumed that the natural part of the Antarctic sea ice extent (SIE) exhibits only short-term persistence, which can be modeled by an auto-regression process of first order (AR(1))
We presented evidence that the temporal evolution of the Antarctic SIE is characterized by a superposition of both, short-term persistent and long-term persistent processes

Summary

OPEN Increase of the Antarctic Sea Ice

Extent is highly significant only in the Ross Sea received: 11 October 2016 accepted: 14 December 2016. In the previous calculations of the trend significance, it has been assumed that the natural part of the Antarctic SIE exhibits only short-term persistence, which can be modeled by an auto-regression process of first order (AR(1)) In this case, the autocorrelation function C(s) decays exponentially with time lag s as C (s) = C(1)s ≡ exp(−s/sx), and the statistical significance of the Antarctic SIE trend can be determined from the classic method developed by[26] (see “Method” section). We suggest that the natural variability of the Antarctic SIE can be described by a superposition of short- and long-term persistence processes, which can be modeled by (see “Method” section). Under the assumption of a purely long-term persistent process (blue line), the trends in the Ross Sea and entire Antarctica are highly significant, with p values below 0.01.

Discussion and Conclusion

Data and Methods

Methods

Findings

Additional Information