Sea Ice South (3): The Logical Song
This may be the most complex blog I have ever written. I will try to put together the material from the previous three blogs to expose the basics of sea ice in the Southern Hemisphere. The first in the series examined the Northern Hemisphere, and the amount of accumulated heat that is needed to explain the melting of sea ice in the north. The second in the series looked at the geography of the planet and the characteristics that distinguish the Arctic from the Antarctic. The third in the series looked at some of the basics principles of the Earth’s climate. All of these set the foundation that there is little reason for the behavior of sea ice in the southern hemisphere to mimic the sea ice in the northern hemisphere. And following that, there is no reason that the response of sea ice to a warming planet will be the same in the northern and southern hemispheres.
First some summary facts: Remember that sea ice is made by the sea freezing. Such freezing occurs at high latitudes, where even as the planet warms up, it will still get cold in the winter because the Sun will still go down for a long time. Sea water is salty, and snow and rain and melting ice sheets on the land are fresh water. Salt water freezes at colder temperatures than fresh water – that’s why we salt icy highways. Finally, much of the heat that gets to the poles is by transport of heat from warmer, lower latitudes.
Let’s start with a figure, which is an annotated version of the map from the second blog in the series.
Figure 1: An annotated map of the South Polar Regions.
I drew a little arrow with a “1” in it at the southern tip of Africa. This is to show how the Agulhas Current comes south on the west African coast as a compact current. It then gets swept away towards the west. Therefore, this current does not directly warm the highest latitudes of the ocean. Therefore, this current does not send a concentrated stream of warm water to the pole that can melt ice. (Contrast this with the Gulf Stream in the Northern Hemisphere, which famously warms the North Atlantic and Arctic regions.)
An understanding of the cause of the spread of the Agulhas Current starts with the big green, dashed arrows on the map. These arrows represent atmospheric storms, which start in middle latitudes, propagate south and turn to the east with the Earth’s rotation. Because of the belt of open water that surrounds Antarctica and the high terrain of Antarctica these storms form a belt of high winds. These winds put stress on the ocean and start the surface of the water moving from west to east. As this water moves from west to east it is diverted northwards, again, due to the rotation of the Earth. (For those who do atmospheric and ocean motion, this is the Coriolis force.) The net result of the atmospheric storms in the Antarctic Ocean is a broad surface current from west to east with a northward deflection. Therefore, at its coast, Antarctica is somewhat isolated from the direct effects of warming. (Look at the map closely and you will see that the 1894 cartographer drew it all in.)
What about under the surface? Under the surface of the southern ocean it is warming, and that warm water is propagating towards Antarctica. It is bringing heat to the edge of the continent and to the bottom of the sea ice. Therefore there is the real possibility of the sea ice melting from below, or if not melting, freezing more slowly.
But sea ice is complicated – if nothing else, that is a message from all of my sea ice blogs. If you look at sea ice in the Southern hemisphere it is increasing on average. But it bounces around a lot and in some places it is systematically increasing and other places it is decreasing. Here’s a picture to remind you of what sea ice was doing back in April.
Figure 2: Areal extent of April sea ice in the Southern Hemisphere from 1979 – 2011. (figure from National Snow and Ice Data Center)
This simultaneous occurrence of growth and melting, cooling and warming, should always be suggestive of the oceans and atmosphere mixing hot and cold. That is what weather is always doing - mixing, trying to even it all out. Whenever there is mixing by fluids, and air and water are both fluids in regard to the way they move – whenever there is mixing by fluids, it gets complicated. Slowly drip heavy cream into gently stirred coffee and watch it stretch and mix.
To make it more complex sea ice is made by freezing water with various levels of salt in it. There is snow and rain, fresh water, falling on the sea ice. There is fresh water coming from melting glaciers pouring into the ocean. Fresh water is heavier that salt water, so if fresh water is on top of salt water, it’s happy. But if saltier water is on top of fresher water it sinks, and causes mixing as fresher water comes up to take its place. Of course, it does not stop there, snow is an insulator and if it is on top of ice, it insulates it from both warm and cold extremes of air temperature. And, remember, when it is cold enough to snow, it snows more in a warmer climate. Hence, there is the possibility of growing protective insulation from the warming air. Salt water, fresh water, insulation – what would happen if it got warm enough that it started to rain more instead of snow. What happens when rain falls on snow and ice? It accelerates melting.
Finally, but perhaps not completely, in Antarctica we have the the ozone hole. And ozone is a greenhouse gas, and in the ozone hole there is a huge decrease of ozone. If there is a large decrease of a greenhouse gas, then that would allow the Earth to more easily emit radiation to space, and it would contribute to cooling.
I want to try two more figures. These figures are, in my best tradition, home-grown schematics to get across some of these ideas.
Figure 3: A historical situation where mixing in the upper layer of the ocean, caused by the density differences between fresh and salt water, brings heat from the warmer sub-surface water and the atmosphere to melt sea ice.
Figure 4: A present or future scenario where mixing in the upper layer of the ocean is suppressed because of the presence of more fresh water at the surface. This reduces heat transport from the warmer sub-surface water and the atmosphere.
In the top of the figure we have what might be called a historic situation. There is warm water under the part of the ocean that is well mixed by the stress of the atmospheric storms. There is some snow. There is a pattern of thawing and freezing of sea ice that yields saltier water on top of fresher water. This causes mixing, and with the warmer and warming ocean below, this brings warm water up, and can melt sea ice more quickly. This can also mix in warming air from the atmosphere.
In the bottom figure there is more snow, maybe rain, because the atmosphere is warming and holds more water and precipitates more strongly. The snow insulates the ice from the atmosphere. That snow changes the balance of fresh and salty water at the surface. It ends up with fresher water on the surface. The mixing is decreased; the warmer and warming ocean below is isolated from the surface from the ice and there is decreased melting.
Given all of this it is not only plausible, but perhaps even expected that there will be times and places with more sea ice. Fresh water is worth a couple of degrees of temperature. I am not an expert on this subject, which is why it has taken me a while to put it together. I got started thinking about this because of a conversation with Cecilia Bitz about the work of her student, Clark Kirkman IV. If you look at this paper you see a more detailed study of the mechanisms described above, but you also see that the predictions of climate models are for a “delay” in Antarctica compared with the Arctic. Also, it is seen that some of the models predict regional cooling in the Antarctic. Their work is available here: Kirkman IV and Bitz, 2010. I provide a larger set of references below.
Finally, there are the crabs and maybe the sharks. In the first blog in the series, about the Arctic, I talked about the significance of accumulating heat in the environment. This accumulation of heat over many years is convincing and compelling evidence of systematic warming. Such evidence is expressed in the onset of spring coming earlier, trees species and animals moving to new regions, large pieces of ice on mountains melting.
Figure 5: The Antarctic Peninsula (map from The Traveling Naturalist)
In that part of Antarctica that reaches out towards the tip of South America, the Antarctic Peninsula, the water has been warming. This has led to migration of king crabs, who now find water warm enough to survive. This, of course, leads to massive shifts of the ecosystem. Looking at warming and possible changes to the surface ocean currents, it is within the realm of possibility that species, such as sharks, will migrate more southward.
Sea ice formation and melting is strongly dependent on how low latitude heat is delivered to poles by motions in the oceans and atmosphere. Local conditions of saltiness impact not only the freezing and thawing, but the mixing of heat in the upper layer of the ocean. The energy exchange between the surface of the ice and the rest of the environment is impacted by rain, snow, clouds, sun, greenhouse gases, soot, algae – the list goes on. Large changes in sea ice formation and extent depend on relatively small, 1 watt per square meter, changes in energy. That is a change of 1 out of 100s. There are many paths that can lead to changes of 1, either positive (warming and melting) or negative ( cooling and freezing). But the fact is that the surface of the Earth and the atmosphere is warming. The ocean is accumulating heat. If there are patches of cooling related to local processes, this cooling is vulnerable to the building heat in the environment. It does not represent either a refutation of the basic tenets of predictions of a warming planet or a measure of global self healing.
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Some primary references:
Kirkman IV and Bitz, 2010 / The Effect of the Sea Ice Freshwater Flux on Southern Ocean Temperatures in CCSM3: Deep Ocean Warming and Delayed Surface Warming
Liu and Curry, 2010 / Accelerated warming of the Southern Ocean and its impacts on the hydrological cycle and sea ice
Turner et al. 2009 / Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent
Zhang, 2006 / Increasing Antarctic Sea Ice under Warming Atmospheric and Oceanic Conditions
Some popular references:
Resolving the Paradox of the Antarctic Sea Ice
Global Warming Protects Antarctic Sea Ice — But Not For Long
Increasing Antarctic Sea Ice Extent Linked to Ozone Hole
King Crabs Invade Antarctic Waters
Crab, Shark Invasion May Threaten Antarctic Marine Life
(If you want to see cool movies that show how rotation organizes flow go to MIT and look at these movies.)
Useful links
Recent sea ice trends
Sea ice data
Rood’s Blogs on Ice
Reader Comments
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Ah, Cat, we've been over this before. Labeling a person a "denialist" or an "alarmist", or a "non-believer" or a "believer", or a "skeptic" or a "supporter", is simple and easy shorthand, much like labeling a person a liberal or a conservative. There's a world of difference between that and calling someone, say, a "cottonheaded ninnymuggins" (Elf) or a "neo-maxi zoom dweebie" (Breakfast Club). Most adults know that, I believe.
Folks can claim otherwise all they wish, but experts* know the current warming is primarily due to increasing concentrations of CO2 due to the unimpeded burning of fossil fuels. Period.
* - climate scientists
Sigh...
Nice try, but no. That's the namby-pamby, wishy-washy, can't-we-all-just-get-along approach that works in Disney cartoons, but not so much in real life. You may label yourself a skeptic, and I may label you a denialist; in neither case is that name-calling, nor is it in any way counterproductive. It's simply a handy and well-understood label. Please try not to confuse the two. Thanks!
(BTW, for all the high-fiving below, no one has yet to provide evidence of the name-calling atmo accused me of. Anybody have that yet? Anybody? Anybody? Anybody?)
And, your usual name calling, denialist, refers to someone with denialism and is far more derogatory than you pretend to believe in this discussion (c'mon, tell us how you really feel).
wiki: Denialism is choosing to deny reality as a way to avoid an uncomfortable truth: [it] is the refusal to accept an empirically verifiable reality. It is an essentially irrational action that withholds validation of a historical experience or event.
Now, with the sun having risen yesterday, one that adheres to a negative position of this notion in the face of "empirically verifiable data" is clearly a denialist.
In AGW-land, the roots of the word denialism are just what is debatable. Truth, verifiable, reality. Given that climate forecasting of future conditions will never be "verifiable", debating that part of AGW will never lend itself to the "denialist" label. One that disagrees that the Himalayas will be completely ice free in the next 30 years (see IPCC referencing enviro-fiction), given that there was no science conducted and zero "empirically verifiable data" exists to support such a notion, should not be called a denialist. One that disagrees that an average global temperature has risen between 1979 and now probably should, though maybe not here given the rules.
Finally, my assertion stands that you, sir, are not called equally derogatory terms such as "alarmist" or "warmista" in every other post, and persist with "denialist" quite regularly.
Well, now, you've thrown a lot into your comment. I won't bore everyone by trying to address everything, but I'd like to hit on a few points if I may.
1) If you folks are uncomfortable with the "denialist" label, what would you prefer? Because as often as I write on this subject, I'm going to continue with a relative economy of words and avoid using any variant of the lengthy "person who is unconvinced of, or simply refuses to believe, the science behind the theory of anthropogenic global warming". Dr. Masters uses "contrarian"; will that work? How about "denier", or is that too close to "denialist"? "Unconvinced", as has been suggested, doesn't quite cover it (though "unconvinceable" might). Likewise "skeptic", since most are anything but. Please tell me; I'm all ears, and I really don't want to hurt any tender feelings.
2) Stating that "average global temperatures [have] not risen since 1979" is verifiably untrue, of course. Is that indeed your assertion? Or did I misread that sentence?
3) I appreciate you stating that you never saw my comment #4, though you earlier accused it of being "rife with name-calling". That's probably as close to an apology as I'll ever get from you, so that'll work. ;-)
I use some variant of "AGW theory proponent" often, maybe an equally innocuous antithesis would suffice?
you cant
so shut up, quit denying natural science, and accept erosion with a smile on your face
Tell Basatardi that may happen when this
Show me a glacier that exists for tens of thousands--or hundreds of thousands--of years in a stable state, then melts to nothingness, or near nothingness, over the span of a few decades. Multiply that single glacier by several hundred around the globe. Then come back here and try to make the case that the planet isn't warming.
1) The sun has been at very low levels of activity for a while, yet the atmosphere has stubbornly refused to cool, choosing instead to keep warming, and warming, and warming...
2) When are Bastardi's legions of loyal followers going to realize his repeated cries of, "This year will be the year things start cooling off!" are about as credible as Rev. Harold Camping's repeated predictions of the Rapture?
3) As you may know, a warmer atmosphere holds more moisture, moisture that precipitates out as rain and, yes, snow.
show me it hasn't happend before in history
you cant
because everything you base your knowledge on is 100 years or less in field research
show me the proof the planet's warming is atmospheric and not tectonic
you cant
because no one has stuck thermometers deep in the crust at various zones
all of the angles have not been researched well enough so a conclusion so far in the quest for the truth would be scientifically dumb at best to assume the planet is warming
and heading toward an iceless future with what we understand already
I'm pretty sure you meant "I don't."
Scientific evidence points in one direction...we are contributing to at least some extent. If you wish to follow the logical fallacy (ad populum), then you are still wrong since the majority of climate scientists believe man is responsible to some extent.
Significant Role Played by Oceans in Ancient Global Cooling
ScienceDaily (May 26, 2011) — Thirty-eight million years ago, tropical jungles thrived in what are now the cornfields of the American Midwest and furry marsupials wandered temperate forests in what is now the frozen Antarctic. The temperature differences of that era, known as the late Eocene, between the equator and Antarctica were only half of what they are today. A debate has long been raging in the scientific community on what changes in our global climate system led to such a major shift from the more tropical, greenhouse climate of the Eocene to the modern and much cooler climates of today.
New research published in the journal Science, led by Rensselaer Polytechnic Institute scientist Miriam Katz, is providing some of the strongest evidence to date that the Antarctic Circumpolar Current (ACC) played a key role in the major shift in the global climate that began approximately 38 million years ago. The research provides the first evidence that early ACC formation played a vital role in the formation of the modern ocean structure.
The paper, titled "Impact of Antarctic Circumpolar Current development on late Paleogene ocean structure," is published in the May 27, 2011, issue of Science.
"What we have found is that the evolution of the Antarctic Circumpolar Current influenced global ocean circulation much earlier than previous studies have shown," said Katz, who is assistant professor of earth and environmental science at Rensselaer. "This finding is particularly significant because it places the impact of initial shallow ACC circulation in the same interval when the climate began its long-term shift to cooler temperatures."
There has been a debate over the past 40 years on what role the Antarctic Circumpolar Current had in the underlying cooling trend on Earth. Previous research has placed the development of the deep ACC (greater than 2,000 meters water depth) in the late Oligocene (approximately 23-25 million years ago). This is well after the global cooling pattern had been established. With this research, Katz and her colleagues used information from ocean sediments to place the global impact of the ACC to approximately 30 million years ago, when it was still just a shallow current.
Oceans and global temperatures are closely linked. Warmer ocean waters result in warmer air temperatures and vice versa. In the more tropical environs of the Eocene, ocean circulation was much weaker and currents were more diffuse. As a result, heat was more evenly distributed around the world. This resulted in fairly mild oceans and temperatures worldwide, according to Katz. Today, ocean temperatures vary considerably and redistribute warm and cold water around the globe in significant ways.
"As the global ocean currents were formed and strengthened, the redistribution of heat likely played a significant role in the overall cooling of the Earth," Katz said.
And no current is more significant than the ACC. Often referred to as the "Mixmaster" of the ocean, the ACC thermally isolates Antarctica by preventing warm surface waters from subtropical gyres to pass through its current. The ACC instead redirects some of that warm surface water back up toward the North Atlantic, creating the Antarctic Intermediate Water. This blocking of heat enabled the formation and preservation of the Antarctic ice sheets, according to Katz. And it is this circumpolar circulation that Katz's research concludes was responsible for the development of our modern four-layer ocean current and heat distribution system.
To come to her conclusions, Katz looked at the uptake of different elemental isotopes in the skeletons of small organisms found in ocean sediments. The organisms, known as benthic foraminifera, are found in extremely long cores of sediments drilled from the bottom of the ocean floor.
During their lifetime, foraminifera incorporate certain elements and elemental isotopes depending on environmental conditions. By analyzing the ratios of different isotopes and elements, the researchers are able to reconstruct the past environmental conditions that surrounded the foraminifera during their life. Specifically, they looked at isotopes of oxygen and carbon, along with ratios of magnesium versus calcium. More detailed information on Katz's isotopic analysis methods can be found at http://green.rpi.edu...ils/index.html.
Analysis of these isotopes from sediment cores extracted directly off the North American Atlantic coast showed the earliest evidence for the Antarctic Intermediate Waters, which circulates strictly as a direct consequence of the ACC. This finding is the first evidence of the effects of shallow ACC formation. The findings place development of the ACC's global impact much closer to the time that Antarctica separated from South America. It had previously been thought that the currents moving through this new continental gateway could not be strong enough at such shallow depths to affect global ocean circulation.
Katz points out that the larger cooling trend addressed in the paper has been punctuated by many short, but often significant, episodes of global warming. Such ancient episodes of warming are another significant aspect of her research program, and play an important role in understanding the modern warming of the climate occurring on the planet.
"By reconstructing the climates of the past, we can provide a science-based means to explore or predict possible system responses to the current climate change," Katz said.
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