Posted on 01/17/2019 12:42:29 PM PST by ETL
Sea ice cover in Antarctica shrank rapidly to a record low in late 2016 and has remained well below average. But what's behind this dramatic melting and low ice cover since?
Our two articles published earlier this month suggest that a combination of natural variability in the atmosphere and ocean were to blame, though human-induced climate change may also play a role.
What happened to Antarctic sea ice in 2016?
Antarctic sea ice is frozen seawater, usually less than a few metres thick. It differs from ice shelves, which are formed by glaciers, float in the sea, and are up to a kilometre thick.
Sea ice cover in Antarctica is crucial to the global climate and marine ecosystems and satellites have been monitoring it since the late 1970s. In contrast to the Arctic, sea ice around Antarctica had been slowly expanding (see figure below).
However, in late 2016 Antarctic sea ice dramatically and rapidly melted reaching a record low. This piqued the interest of climate scientists because such large, unexpected and rapid changes are rare. Sea ice coverage is still well below average now.
We wanted to know what caused this unprecedented decline of Antarctic sea ice and what changes in the system have sustained those declines. We also wanted to know if this was a temporary shift or the beginning of a longer-term decline, as predicted by climate models. Finally, we wanted to know whether human-induced climate change contributed to these record lows.
Hunting for clues
Sea ice cover around Antarctica varies a lot from one year or decade to the next. In fact, Antarctic sea ice cover had reached a record high as recently as 2014.
That provided a clue. As year-to-year and decade-to-decade sea ice cover varies so much, this can mask longer-term melting of sea ice due to anthropogenic warming.
The next clue was in records broken far away from Antarctica. In the spring of 2016 sea surface temperatures and rainfall in the tropical eastern Indian Ocean were at record highs. This was in association with a strongly negative Indian Ocean Dipole (IOD) event, which brought warmer waters to the northwest of Australia.
While IOD events influence rainfall in south-eastern Australia, we found (using both statistical analysis and climate model experiments) that it promoted a pattern in the winds over the Southern Ocean that was particularly conducive to decreasing sea ice.
These surface winds blowing from the north not only pushed the sea ice back towards the Antarctic continent, they were also warmer, helping to melt the sea ice.
These northerly winds almost perfectly matched the main regions where sea ice declined.
Though previous studies had linked this wind pattern to the sea ice decline, our studies are the first to argue for the dominant role of the tropical eastern Indian Ocean in driving it.
But this wasn't the only factor.
Later in 2016 the typical westerly winds that surround Antarctica weakened to record lows. This caused the ocean surface to warm up, promoting less sea ice cover.
The weaker winds started at the top of the atmosphere over Antarctica, in the region known as the stratospheric polar vortex. We think this sequential occurrence of tropical and then stratospheric influences contributed to the record declines in 2016.
Taken together, the evidence we present supports the idea that the rapid Antarctic sea ice decline in late 2016 was largely due to natural climate variability.
Since then, sea ice has remained mostly well below average in association with warmer upper ocean temperatures around Antarctica.
We argue these are the product of stronger than normal westerly winds in the previous 15 or so years around Antarctica, driven again from the tropics. These stronger westerlies induced a response in the ocean, with warmer subsurface water moving towards the surface over time.
The combination of record tropical sea surface temperatures and weakened westerly winds in 2016 warmed the entire upper 600m of water in most regions of the Southern Ocean around Antarctica. These warmer ocean temperatures have maintained the reduced extent of sea ice.
Antarctic sea ice extent is seeing a record low start to the New Year. It suggests the initial rapid decline seen in late 2016 was not an isolated event and, when combined with the decadal-timescale warming of the upper Southern Ocean, could mean reduced sea ice extent for some time.
We argue what we are seeing so far can be understood in terms of natural variability superimposed on a long-term human-induced warming signal.
This is because the rainfall and ocean temperature records seen in the tropical eastern Indian Ocean that led to the initial sea ice decline in 2016 likely have some climate change contribution.
This warming and the recovery of the Antarctic ozone hole may also impact the surface wind patterns over coming decades.
Such changes could be driving climate change effects that are starting to emerge in the Antarctic region. However the limited data record and large variability indicate it's still too early to tell.
We would like to acknowledge the role of our co-authors S Abhik, Cecilia M Bitz, Christine TY Chung, Alice DuVivier, Harry H Hendon, Marika M Holland, Eun-Pa Lim, LuAnne Thompson, Peter van Rensch and Dongxia Yang in contributing to the research discussed in this article.
Explore further: Record-low 2016 Antarctic sea ice due to 'perfect storm' of tropical, polar conditions
91 volcanoes? Hey progs believe The Guardian.
https://www.theguardian.com/world/2017/aug/12/scientists-discover-91-volcanos-antarctica
No conclusions. Only more questions.
Crab People.
Uh, it’s summer down under currently?
As Arnold always says... “I’ll be back” and so will the ice... The funny part... All this concern about Ice, but planet earth has actually existed for most of it’s life without ice. Completely ice free in fact.
From the internets... “There have been at least five major ice ages in the Earth’s history (the Huronian, Cryogenian, Andean-Saharan, Karoo Ice Age, and the current Quaternary Ice Age). Outside these ages, the Earth seems to have been ice free even in high latitudes.”
My take on that quote... Let’s get rid of the ice.
Maybe global warming is real but is caused by all the hot air being generated by politicians in DC and by all the rabid climate change environmentalist.
Polar bears are eating too many snow cones.
Two miles under the ice are tree stumps.
Same with Greenland (less ice).
The record low amount of ice in Antarctica is: ZERO.
There is no such thing as ‘static climate’. It is always changing. I suspect the recent change is due to the movement of the magnetic north pole.
You gave the truth to the mystery that the Left does not want us to know. I was just going there and you beat me to it. Ice melting from 91 volcanoes will not be fixed with any energy policy.
Do a search of the coming SOLAR MINIMUM...unlike global warming....this is REAL!!!
You’ll notice that the media is ignoring this....another sign of its reality.
Hmmmn.
And, from 1992 through the middle of 2015, the Antarctic sea ice was steadily growing, all during the same period global CO2 levels increased by more than 1/3. Odd that.
In fact, in June 2014, the Antarctic seaa ice anomaly - the daily difference of that day’s sea ice area from its 30 year average, was 2.16 million sq kilometers - an area greater than the entire area of Greenland!
Shortly thereafter, those same researchers from the University of Illinois Cryosphere Center who had been tracking the Antarctic Sea ice were retired out, and replaced by new people. The Antarctic sea ice area reports stopped from Cryosphere stopped after those retirements, and the new values from the “more reliable” federal center at NSIDC Boulder CO dropped 1.5 million sq kilometers. In 2 months.
Funny that.
I've posted tons of stuff on the Sun-climate connection, as it relates to solar activity and galactic cosmic rays.
NASA actually has a piece on it on its SOHO page. But it's deeply buried and very difficult to find. It's in their "Not So Frequently Asked Questions" section. No joke.
From NASA's Solar and Heliospheric Observatory's "Not So Frequently Asked Questions" section:
Q-Does the number of sunspots have any effect on the climate here on Earth?
A-Sunspots are slightly cooler areas on the surface of the Sun, due to the intense magnetic fields, so they radiate a little less energy than the surroundings. However, there are usually nearby areas associated with the sunspots that are a little hotter (called falculae), and they more than compensate. The result is that there is a little bit more radiation coming from the Sun when it has more sunspots, but the effect is so small that it has very little impact on the weather and climate on Earth.
However, there are more important indirect effects: sunspots are associated with what we call "active regions", with large magnetic structures containing very hot material (being held in place by the magnetism). This causes more ultraviolet (or UV) radiation (the rays that give you a suntan or sunburn), and extreme ultraviolet radiation (EUV). These types of radiation have an impact on the chemistry of the upper atmosphere (e.g. producing ozone). Since some of these products act as greenhouse gases, the number of sunspots (through association with active regions) may influence the climate in this way.
Many active regions produce giant outflows of material that are called Coronal Mass Ejections. These ejections drag with them some of the more intense magnetic fields that are found in the active regions. The magnetic fields act as a shield for high-energy particles coming from various sources in our galaxy (outside the solar system). These "cosmic rays" (CRs) cause ionization of molecules in the atmosphere, and thereby can cause clouds to form (because the ionized molecules or dust particle can act as "seeds" for drop formation).
If clouds are formed very high in the atmosphere, the net result is a heating of the Earth - it acts as a "blanket" that keeps warmth in.
If clouds are formed lower down in the atmosphere, they reflect sunlight better than they keep heat inside, so the net result is cooling. Which processes are dominant is still a matter of research.
http://sohowww.nascom.nasa.gov/classroom/notsofaq.html#SUNSPOT_CLIMATE
Uhm... It’s summer in Antarctica... Or, did they miss the memo?
Need to know what “the recovery of the Antarctica ozone hole” means in English.
Is “recovery” meaning the “closing” of the hole or the expansion of it?
Otherwise, an interesting article and the presence of so many undersea/continent volcanoes means that they have to have some type of influence on the underlying rock formations of the continent, possibly inducing warming under the bottom layers of continental ice.
Meanwhile, all my birds packed their travel bags today and headed for Puerto Rico, figuring that if it was good enough for the Democ-Rats, it was good enough for them. Only they are paying their own way.
Lol! They probably mean the 'closing' of the hole.
The ozone hole is not technically a “hole” where no ozone is present, but is actually a region of exceptionally depleted ozone in the stratosphere over the Antarctic that happens at the beginning of Southern Hemisphere spring (August–October).
Satellite instruments provide us with daily images of ozone over the Antarctic region. The ozone hole image below shows the very low values (blue and purple colored area) centered over Antarctica on 4 October 2004. From the historical record we know that total column ozone values of less than 220 Dobson Units were not observed prior to 1979.
From an aircraft field mission over Antarctica we also know that a total column ozone level of less than 220 Dobson Units is a result of catalyzed ozone loss from chlorine and bromine compounds.
For these reasons, we use 220 Dobson Units as the boundary of the region representing ozone loss. Using the daily snapshots of total column ozone, we can calculate the area on the Earth that is enclosed by a line with values of 220 Dobson Units (the white line in the figure below).
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