Wednesday, October 30th 2019, 7:40 pm - Arctic Sea Ice extent has been at very low levels for 2019
On September 18, Arctic sea ice reached its minimum summer extent for 2019.
Since 1979, this minimum extent, at just 4.153 million square kilometres, was the second lowest on record. Only 2012 definitively saw a lower extent than this.
This map shows the September 18, 2019 Arctic Sea Ice extent (blue-white), compared to the 1981-2010 average minimum extent (red line). Credit: NASA Goddard
Arctic sea ice extent has already been very low for this year. It spent the first three months of the year at the third lowest extent or better. It then dipped to record lows three times - for the entire month of April, then again for a few days in mid-June, and once again from July 8 through August 13 - before it reached the second-lowest minimum extent in mid-September.
Even as the extent began to grow towards the end of September and through October, it once again slipped to the lowest extent on record for the entire second half of this month.
Arctic sea ice extent from July through November, for 2012 (the current record lowest extent), 2016 and 2019. Credit: NSIDC
A warmer Arctic means a weakened and more erratic jet stream - and perhaps somewhat paradoxically, the possibility of more frequent winter outbreaks of periodic extreme cold at lower latitudes. Just because it is cold at your location doesn't mean it is cold everywhere!Kyle Brittain on Twitter
As Kyle Brittain mentioned on Twitter, there's an impact this can have on the weather.
Less bright ice covering the Arctic ocean means there's more dark water surface. This results in more solar radiation being absorbed by that dark water, when it would normally (in the case where the ice extent was at more normal levels) be reflected back into space by bright ice. As more solar radiation is absorbed, more heat is emitted by the water as it slowly freezes, and this raises air temperatures in the Arctic.
Research is showing us that this can have a dramatic effect on winters for Canada and the United States, due to the impacts these warmer temperatures have on the polar vortex. The polar vortex is a natural counter-clockwise flow of air high in the stratosphere above the Arctic, which is linked to the polar jet stream, a meandering ribbon of strong winds that flows close to the top of the troposphere (where most of Earth's weather takes place).
The polar vortex circles the Arctic, with the polar jet extending L.S. Gardiner/UCAR, CC BY-ND
A strong polar vortex means that the winds in the polar jet stream tend to flow faster, and this tightens up the flow of the jet stream so that any bumps and wiggles in the ribbon are usually small. This is the case when there is a large difference in temperature between the equator and the north pole.
If the temperature difference between the equator and the pole gets smaller, though, as the Arctic warms at a faster rate than the equator, the polar vortex weakens. This slows down the jet stream flow, and allows larger bumps and wiggles to develop in the ribbon. These larger meanderings of the jet stream not only extend farther south, but they move along at a slower pace. This can lead to prolonged outbreaks of extremely frigid winter conditions across regions that are simply not used to that kind of weather.
This was seen most dramatically in the winter of 2013-2014.
The normal, stronger polar vortex is shown to the left, with a fairly stable polar jet stream. On the right, the weaker polar vortex in early 2014 leads to a wavier jet stream and a detached low pressure system over the United States. Credit: NASA
What kind of effect will this have for the coming winter? We will have to see exactly how quickly the sea ice extent grows from here on.
This does point to the continuing trend of sea ice loss for the Arctic, though. In 2012, we saw the lowest summer minimum extent for Arctic sea ice since record keeping began in 1979. As of now, however, 2016 holds the record for lowest yearly Arctic average extent.
With sea ice extent in 2019 tracking at below 2016 levels for more than a third of the year so far, it's possible we could see a new lowest yearly average extent in the record books for the Arctic once the year is over. Also, at the other end of the Earth, with 2016-2019 Antarctic sea ice extents tracking at or near their lowest levels on record, this could add up to a global annual average extent for 2019 that beats out 2017 for the lowest so far, as well.