September 19, 2020

Arctic Sea ice plunges to record low extent for late Winter

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climatereanalyzer_anomaly_GFS33hr_9Z_3.10.15By: Bob Henson From Weather Underground

Instead of easing toward its typical March maximum in coverage, the Arctic’s sea ice appears to be more inclined toward getting a head start on its yearly summer melt-out. As of Sunday, March 8, Arctic sea ice as calculated by Japan’s National Institute of Polar Research extended across 13.65 million square kilometers (Figure 1, red line). This value is more than 450,000 sq km–roughly the size of California–below the record extent for the date.

Figure 1. Arctic sea ice in 2015 (red trace) may have already reached its maximum extent for the year. Image credit: National Institute of Polar Research (Japan).

noaa_ao_3.9.15Even more striking is the consistency of the ice loss over the last couple of weeks. March is often a time of rapid gains and losses in ice cover, as seasonal warming and melting battle it out with quick refreezing when shots of cold air return. This year, the ice extent peaked on February 15 at 13.94 million sq km, and it looks increasingly unlikely that the ice will manage to return to that very early peak over the next couple of weeks. No season in the Japanese database has fallen short of the 14-million mark, so if the February peak stands, it will mark the lowest maximum in the Arctic since satellite monitoring began in 1979.

Using a slightly different formula for calculating extent, the National Snow and Ice Data Center comes up with a similar record low for the date (Figure 2). In an update on March 4, NSIDC stated: “The Arctic maximum is expected to occur in the next two or three weeks. Previous years have seen a surge in Arctic ice extent during March (e.g., in 2012, 2014). However, if the current pattern of below-average extent continues, Arctic sea ice extent may set a new lowest winter maximum.” (As explained by NSIDC, “extent” measures the outer edge of where ice covers most of the ocean surface, with at least 15 percent of ice coverage required in a given grid cell. It’s a bit like measuring the size of a slice of Swiss cheese. “Area” is a more direct index of where ice actually exists–the cheese itself–but it’s also more prone to difficulty in satellite measurement.)

ijis_extentFigure 2. A closer look at Arctic sea ice extent for each year since 2007. Image credit: National Snow and Ice Data Center/Charctic.

Not only is Arctic sea ice essential to many ecosystems: it serves as a powerful tracer of recent warming, and its absence in summer allows open water to absorb much more heat from sunlight. While the ice has seen some modest recovery in recent years, it has failed to fully mend the fabric torn by the record-setting drop of 2007. The overall thickness of the ice, and the fraction that’s survived for multiple years (multiyear ice), have both suffered major losses. A comprehensive survey just published in The Cryosphere found that ice thickness in the central Arctic dropped by 65 percent from 1975 to 2012.

Experts differ strongly on when we might see a summer that melts nearly all of the Arctic’s ice (typically defined as less than a million sq km of extent by the normal September minimum). Computer models suggest this point might not be reached till the 2040s or later, while simple extrapolation from recent years would produce an effectively ice-free September by the 2020s, perhaps even sooner. Sea ice around Antarctica has increased somewhat in recent years, but that ice plays a vastly different role in global and regional climate.

A lot can happen during a particular Arctic warm season to accelerate or mute ice loss. Melt ponds scattered across the ice play a vital role in absorbing sunlight and hastening further melt, and cloud-free, sunny weather–especially near the summer solstice–can make a huge difference. Because of these and other intervening factors, there’s little correlation between the size of the March (or February) maximum and that of the September minimum. Even so, the magnitude of the current record low for the date is jarring, and weather patterns this week could raise eyebrows even further. A string of intense cyclones is now riding the jet stream northward between Greenland and Norway. The flow around these storms is close to ideal for pushing large amounts of ice to their doom through the Fram Strait east of Greenland. Such export of ice is more common when the Arctic Oscillation is positive, as it’s been most of this winter. NOAA’s daily AO index reached an extremely high value over the past weekend, exceeding 5.5.

Figure 3. The daily Arctic Oscillation index was nearly off the charts on the high side during the weekend of March 7-8, 2015. Image credit: NOAA Climate Prediction Center.

nsidc_3.8.15The current weather pattern is also pushing a huge pulse of extremely mild late-winter air across the central Arctic (see Figure 4). Temperatures on Sunday, March 8, reached 15.8°C (60.4°F) in Stockholm. Senior climatologist Sverker Hellström (Swedish Meteorological and Hydrological Institute) observed today in an email forwarded by weather records researcher Maximiliano Herrera that the 15.8°C is the warmest reading prior to March 19 in records at Stockholm that go all the way back to 1756! If there is any major refreezing of Arctic sea ice in the next few days, it’s most likely to occur in the Bering Sea, but the freeze-up there would have to be vast and quick to counterbalance the major ice losses we’ve seen across the Arctic as a whole since February. Even if a new peak is reached this month, it’s unlikely to be enough to keep 2015 from setting the record for the lowest maximum Arctic ice extent.

The Arctic Sea Ice Blog offers extensive coverage of this topic, including an excellent compilation of graphics updated daily. Blogger Jim Hunt examined the current situation in a detailed post on Sunday.

Figure 4. A surge of relatively mild air may send temperatures 35°F or more above average over the central Arctic by Tuesday, March 10. Image credit: ClimateReanalyzer.org.

For more on this story go to: http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2929

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