Antarctic sea ice is declining dramatically

A 40-y document reveals gradual Antarctic sea ice will increase adopted by decreases at charges far exceeding the charges seen within the Arctic

Claire L. Parkinson

PNAS first printed July 1, 2019 https://doi.org/10.1073/pnas.1906556116

Contributed by Claire L. Parkinson, Might 24, 2019 (despatched for evaluate April 16, 2019; reviewed by Will Hobbs and Douglas G. Martinson)

Significance

A newly accomplished 40-y document of satellite tv for pc observations is used to quantify modifications in Antarctic sea ice protection because the late 1970s. Sea ice spreads over huge areas and has main impacts on the remainder of the local weather system, reflecting photo voltaic radiation and limiting ocean/ambiance exchanges. The satellite tv for pc document reveals gradual, decades-long total improve in Antarctic sea ice extents reversed in 2014, with subsequent charges of lower in 2014–2017 far exceeding the extra extensively publicized decay charges skilled within the Arctic. The speedy decreases decreased the Antarctic sea ice extents to their lowest values within the 40-y document, each on a yearly common foundation (document low in 2017) and on a month-to-month foundation (document low in February 2017).

Summary

Following over three a long time of gradual however uneven will increase in sea ice protection, the yearly common Antarctic sea ice extents reached a document excessive of 12.eight × 106 km2 in 2014, adopted by a decline so precipitous that they reached their lowest worth within the 40-y 1979–2018 satellite tv for pc multichannel passive-microwave document, 10.7 × 106 km2, in 2017. In distinction, it took the Arctic sea ice cowl a full three a long time to register a loss that nice in yearly common ice extents. Nonetheless, when contemplating the 40-y document as a complete, the Antarctic sea ice continues to have a constructive total pattern in yearly common ice extents, though at 11,300 ± 5,300 km2⋅y−1, this pattern is barely 50% of the pattern for 1979–2014, earlier than the precipitous decline. 4 of the 5 sectors into which the Antarctic sea ice cowl is split all even have 40-y constructive traits which are properly decreased from their 2014–2017 values. The one anomalous sector on this regard, the Bellingshausen/Amundsen Seas, has a 40-y unfavourable pattern, with the yearly common ice extents lowering total within the first three a long time, reaching a minimal in 2007, and exhibiting an total upward pattern since 2007 (i.e., reflecting a reversal in the wrong way from the opposite four sectors and the Antarctic sea ice cowl as a complete).

For the reason that late 1990s, it has been clear that the Arctic sea ice cowl has been lowering in extent over the course of the multichannel passive-microwave satellite tv for pc document begun in late 1978 (1⇓–three). The decreases have accelerated because the 1990s and have been a part of a constant suite of modifications within the Arctic, together with rising atmospheric temperatures, melting land ice, thawing permafrost, longer rising seasons, elevated coastal erosion, and warming oceans (four, 5). General, it has been a constant image solidly consistent with the expectations of the warming local weather predicted from will increase in greenhouse gases. Specifically, modeled sea ice predictions confirmed marked Arctic sea ice decreases, and the precise decreases even exceeded what the fashions predicted (6).

The Antarctic scenario has been fairly completely different, with sea ice extent rising total for a lot of the interval since 1978 (7⇓⇓⇓–11). These will increase have been much more puzzling than the Arctic sea ice decreases and have led to a wide range of steered explanations, from ties to the ozone gap (12, 13; rejected in refs. 14, 15); to ties to the El Niño–Southern Oscillation (ENSO) (16), the Interdecadal Pacific Oscillation (17), and/or the Amundsen Sea Low (10, 13, 17); to ties to basal meltwater from the ice cabinets (18; rejected in ref. 19). None of those has but yielded a consensus view of why the long-term Antarctic sea ice will increase occurred.

Within the meantime, whereas the sudden, decades-long total will increase in Antarctic sea ice extent are nonetheless being puzzled out, the ocean ice extent has taken a dramatic flip from comparatively gradual will increase to speedy decreases. On a yearly common foundation, the height sea ice extent since 1978 got here in 2014. Since then, the decreases have been so nice that the yearly averages for 2017 and 2018 are the bottom in your entire 1979–2018 document, basically wiping out the 35 y of total ice extent will increase in just some years. This dramatic reversal within the modifications occurring within the Antarctic sea ice will present useful additional data to check earlier steered explanations of the long-term Antarctic sea ice will increase. We now have a 40-y multichannel passive-microwave satellite tv for pc document of the Antarctic sea ice cowl, all of which resides within the Southern Ocean. The aim of this paper is to current that document each for the Southern Ocean as a complete (labeled “Southern Hemisphere” within the figures, to emphasise the inclusion of your entire hemispheric sea ice cowl) and for the breakdown of the Southern Ocean into the 5 sectors recognized in Fig. 1.

Fig. 1. Identification of the 5 sectors used within the regional analyses. These are an identical to the sectors utilized in earlier research (7, eight).

Full paper right here. Not paywalled.

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