Antarctic Refrigerator Effect & Climate Sensitivity

Antarctic Refrigerator Effect, Climate Sensitivity & Deformation professionnelle: 

Lessons from Past Climate Change - Part 2

For the past 55 million years the global surface temperature has declined by more than 10°C from a “hot house” condition into an “ice house” with increasing temperature variability as depicted in Figure 1 (Mya = millions of years ago). During the Cretaceous and Early Cenozoic, glaciers and ice caps were absent from both Antarctica and Greenland. Antarctica was covered in para-tropical vegetation and Greenland was home to crocodiles. More importantly for millions of years the oceans had been storing enormous amounts of heat. In contrast to near freezing temperatures today, Antarctic bottom waters averaged about 11°C, suggesting Antarctic coastal temperatures never dropped below 11°C even during the long polar nights.  Amazingly the equator to pole surface temperature difference averaged just 10°C compared to the 30°C gradient measured today. Of particular interest, changes in carbon dioxide fail to explain the greatest proportion of these ancient temperatures.

Figure 1  Cenozoic Evolution of Global Temperatures

For decades the consensus had been that ocean heat transport had ultimately maintained the polar regions’ ancient tropical conditions. Models had demonstrated without heat transport from the tropics, the poles would be 110°C colder than the tropics (Gill 1982, Lozier 2012). It was commonly believed, and is still believed by most, that as plate tectonics rearranged the continents, the Antarctic Circumpolar Current (ACC) formed and strengthened. Models now simulate that as drifting continents opened “gateways” and allowed for uninterrupted circumpolar flow, surface temperatures began cooling significantly (Bijl 2013). A strengthening ACC created a barrier inhibiting intrusions of warm tropical waters and minimizing both oceanic and atmospheric heat transport resulting in the Refrigerator Effect. The Refrigeration Effect radically cooled the southern ocean and altered the vertical temperature structure of all the earth’s oceans. (As discussed here, the ACC barrier to ocean heat transport is a major reason why Antarctic sea ice has currently increased in contrast to decreasing Arctic sea ice.)

However a few climate modelers began arguing CO2, not heat transport, was the ultimate climate control knob. They argued that high CO2 concentrations explained the polar warmth and the decline in CO2 explained the advent of polar ice caps and the 55 million year trend towards our icehouse climate. This debate between heat transport and greenhouse effects not only reveals a lack of climate consensus; it also reveals the subjectivity that influences how climate sensitivity is estimated. Proxy evidence increasingly suggests that ancient CO2 levels were far lower than what climate models require to simulate ancient warmth. In stark contrast to current research that is increasingly suggesting lower climate sensitivity to CO2 (i.e. Lewis & Curry 2014, and a growing list here and here), paleoclimate researchers who argue CO2 controls climate change, are forced to suggest climate sensitivity must have been much, much greater than anyone currently believes.

In contrast, researchers examining the Paleocene‑Eocene maximum temperatures concluded, “At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration, this rise in CO2 can explain only between 1 and 3.5°C of the [5-9°C] warming inferred from proxy records. We conclude that in addition to direct CO2 forcing, other processes and/or feedbacks that are hitherto unknown must have caused a substantial portion of the warming during the Paleocene–Eocene Thermal Maximum. Once these processes have been identified, their potential effect on future climate change needs to be taken into account.” [Emphasis added]  Zeebe (2009). 

However if “unknown feedbacks” and other forcings can explain an even greater proportion of past temperature changes, then researchers would be forced to suggest climate sensitivity to CO2 is much lower. The Antarctic Refrigerator Effect is such an effect and parsimoniously explains Cenozoic global cooling without invoking a CO2 contribution.

The Case Against a CO2 Climate “Control Knob

By creating a well‑mixed global “blanket”, the carbon dioxide greenhouse effect should act on a global scale. However as illustrated in Figure 1, initiation of Antarctic glaciation happened 35 million years ago, more than 30 millions years before Arctic glaciation ever began. Clearly Antarctic glaciation was not part of a global event, but a regional one. Although this gross time difference does not rule out a limited contribution from diminishing CO2 concentrations, the evidence most assuredly demands a different and more regional explanation for the drivers of Antarctica’s observed climate change.

Furthermore, in order for a CO2 greenhouse effect to have created the near‑tropical conditions observed in Antarctica’s fossil evidence, it requires CO2 concentrations far greater than what the growing number of paleo‑proxies are suggesting. Huber (2011) argued that their models could simulate tropical warmth in polar regions  if  CO2 reached 4480 ppm, an 11‑fold increase above today’s concentrations. However Huber 2011 also admitted their estimate of CO2 concentrations should not be taken literally. Instead it was his approach “equivalent to “tuning” climate sensitivity to a higher value, but is much simpler in practice.” They argued that the  “4480 ppm CO2 concentration used here should not be construed literally: it is merely a means to increase global mean warmth.”

Huber 2011 was wise to admit CO2 concentrations of 4480 are unrealistic. Based on growing proxy evidence, CO2 concentrations during the past 350 million years have not exceeded 1000 ppm (Franks 2014). However Huber 2011’s suggestion of greater CO2 climate sensitivity proves to be equally inappropriate and most likely a case of déformation professionnelle.

Deformation professionnelle is a French term referencing how one’s profession narrows and distorts one’s viewpoint and thus biases conclusions. For example if researchers whose funding and status has been driven by a paradigm that CO2 drives all climate change, any contrary evidence will be reinterpreted to maintain that viewpoint.

One major avenue of research strives to determine climate sensitivity by comparing varying CO2 concentrations with past climate change. Although Franks 2014 determined past CO2 variations only accounted for 20% of what Huber’s models required, they too felt obligated to suggest there must be a much greater climate sensitivity to the smaller changes in CO2. But they obviously ignore much more parsimonious inferences. Very simply, there are other dynamics that drive climate change, and current models driven by CO2 have failed to incorporate additional and alternative explanations. Similarly CO2 variations are insufficient to explain the Dansgaard‑Oeschger extreme warming events of the last Ice Age. But as discussed here, changes in ocean heat storage and ventilation offer a superior explanation. Likewise Antarctica’s Refrigerator Effect completely altered ocean heat storage and ventilation and can parsimoniously accounts for Cenozoic global cooling.

Unfortunately evaluations of CO2 climate sensitivity typically only compare varying CO2 concentrations with other estimated radiative effects to explain fluctuations in global mean surface temperatures (GMST).  However there are other powerful non-radiative effects that also contribute to a varying GMST as well as the increasing equator to pole temperature gradient.  For example examining changes in Cenozoic climate  Thomas (2014) concluded, “Stronger vertical mixing within the oceans potentially reconciles several long-standing greenhouse paleoclimate problems. Stronger vertical mixing invigorates the MOC [Meridonal Overturning Circulation] by an order of magnitude, increases ocean heat transport by 50–100%, reduces the zonal mean equator-to-pole temperature gradients by up to 6°C, lowers tropical peak terrestrial temperatures by up to 6°C, and warms high-latitude oceans by up to 10°C.”

Given that just the upper 3.5 meters of the oceans hold more heat than our entire atmosphere. And that average depth of the oceans is an order of 3 magnitudes greater, about 3600 meters; changes in ocean heat storage and ventilation have humongous impacts on global climate. Research that ignores contributions to GMST from ocean heat storage, ventilation and vertical mixing, CO2, will greatly exaggerate climate sensitivity to CO2. Today we witness global warming from heat ventilation during an El Nino and global cooling due to increased upwelling of cooler waters during La Ninas.  On time scales varying from a few years to millions of years, storage and ventilation of ocean heat has been the earth’s true climate control knob.

The Antarctic Refrigeration Effect

Our modern freezer and refrigerator appliances are all based on 2 simple principles. 1) A compressor‑refrigerant apparatus pumps heat out of the refrigerator’s interior. 2) The refrigerator is insulated to minimize any heat transfer into the refrigerator from the outside.

The Antarctic analogy to a refrigerant/compressor apparatus has been ever present. Due to the earth’s spherical shape and orbital effects, annual incoming solar radiation at the poles is so low, polar regions always radiate more heat back to space than is ever absorbed locally. Without a constant flow of heat from the tropics, polar regions would naturally descend into permanent ice house climates. Forcing by CO2 is not a significant factor, if a factor at all. Thus variations in Antarctica’s climate are governed by changes in heat transport versus the steady radiation of heat back to space.  Although Antarctica sat over the South Pole for hundreds of millions of years, it remained ice free for most of the Mesozoic and early Cenozoic because the “refrigerator door” was left open. However as continents began to shift and opened “ocean gateways”, the Antarctic Circumpolar Current (ACC) formed and intensified. The ACC closed the refrigerator door and resisted poleward heat transport from the tropics.  The ACC also generated more intense westerly winds and invigorated upwelling that increased vertical mixing. Most importantly as the ACC shut the refrigerator door, sea ice began forming in the southern seas. That initiated deep ocean cooling and a total reconfiguration of the global ocean’s vertical heat structure.

Before the ACC formed, Antarctic bottom waters were about 11°C. Bottom waters formed from competing regions. In shallow seas that dominated subtropical regions, warm salty water became dense enough to sink to the bottom. Elsewhere warm salty subtropical waters that were transported poleward cooled and sank.  In contrast, once the Antarctic refrigerator was established, cold salty brine was now extruded during sea ice formation. The sinking of cold brine either penetrated to the abyss forming near freezing bottom water, or slowly cooled the subsurface waters as the brine was turbulently mixed with its surroundings. Thus global oceans began a 35 million year cooling trend starting from the ocean abyss and working its way to the surface.

In Figure 13 below (from Kennett 1990), the bottom frame labeled Proteus, illustrates a simplified vertical structure of the Atlantic Ocean around 60 million years ago. Warm Salty Deep Water (WSDW) dominated the ocean depths. Much of that warm bottom water is believed to have been generated in shallow equatorial seas, like the Tethys, where evaporation exceeded precipitation.  Our modern Mediterranean Sea is a remnant of the Tethys, and still contributes warm salty water to the Atlantic.

The surface waters around Antarctica were much fresher because cooler polar regions experience greater precipitation relative to evaporation. Antarctic Intermediate Water (AAIW) forms as upwelling bottom waters mixed with fresher surface waters. Subsequently, climate change has been greatly affected as Antarctic Intermediate Water have cooled and exerted a tremendous effect on tropical sea surface temperatures for millions of years via “ocean tunneling”.

The middle frame of Figure 13, labeled Proto-Oceanus, illustrates how the ocean’s vertical structure evolved over the next 10+ million years after the formation of a strong Antarctic Circumpolar Current. Due to the refrigerator effect, cold saline Antarctic Bottom Water (proto‑AABW) began to dominate the ocean floor. Contributions of Warm Saline Deep Water (WSDW) diminished, and the influential Antarctic Intermediate Water (AAIW) was increasingly cooled by much colder Antarctic Bottom Water. As the colder AAIW flows back towards the equator it modulates the global temperature by cooling subsurface waters that would potentially reach tropical surfaces via upwelling.

 

65 million year Evolution of Ocean Vertical Heat Structure

The upper frame labeled Oceanus, represents a simplified illustration of the Atlantic’s modern vertical structure. Due to the Antarctic Refrigerator Effect, the deep oceans continued to cool, and the thermocline that separates warm surface water from cooler deep waters became increasingly more shallow.

Between 2 and 3 million years ago the cooling of the deep oceans reached a tipping point, and modern upwelling regions ogf cold deep water off the coast of Peru, California and the west coast of Africa were established. There had always been upwelling along those coasts along with the associated increases in marine productivity. But now upwelled subsurface waters were cooler by 4 to 9°C. (Dekens 2007), corresponding to the cooling by Antarctic Bottom waters and its effect on subsurface waters. Analogous to the drop in global temperatures during La Nina events caused by upwelling of colder waters, upwelling of colder waters 2 to 3 million years ago also cooled global temperature to the point it initiated Arctic ice cap and glacier formation. The cooler Arctic then promoted formation of North Atlantic Deep Water (NADW in the upper frame of Figure 13) as salty Atlantic waters transported poleward cooled and brine rejection increased as more Arctic sea ice formed.

Declining CO2: A Result Not A Cause.

The Cretaceous Period (145 to 65 million years ago) was named for huge widespread chalk deposits that developed during that time period, especially in the Tethys Sea. Those chalk deposits were the result of sinking plankton that produced calcium carbonate shells like foraminifera and coccolithophorids, As discussed in Natural Cycles of Ocean Acidification, the creation of calcium carbonate shells pumps alkalinity to depth but produces CO2 at the surface thus adding to higher concentrations of atmospheric CO2.  More enlightening and contrary to catastrophic CO2 assertions that rising CO2 will decimate calcium carbonate shell producers, the greatest proliferation of calcium carbonate shell producers occurred during this period with the high temperatures and high concentrations of atmospheric CO2. Quite likely, high CO2 concentrations did not produce detrimental acidification, and were the result of coccolithophorids and foraminifera pumping CO2 to the surface.

The development of the Antarctic Circumpolar Current forever altered the carbon biological pump by increasing upwelling in the southern oceans, and later along continental west coasts by cooling upwelled waters. When the ACC caused upwelling in southern oceans to intensify, a more reliable supply of nutrients supported the evolution and proliferation of diatoms. As discussed in Natural Cycles of Ocean Acidification, diatoms are large, produce siliceous shells, and more rapidly shuttle CO2 from the surface to ocean depths. As evolving diatom populations expanded, a more efficient biological pump buried more CO2 at depth that is now detected as siliceous ooze or as biogenic opal deposits. In contrast CO2 emitting coccolithophorid populations and their chalk deposits dwindled. Changes in the biological pump contributed to observed declines in atmospheric CO2. Diatoms are also associated with explosive increases in ocean productivity, so it should be no surprise that the earliest appearance and evolution of whales also coincides with increased ACC upwelling and the evolution of diatoms.

In summary, due to continental drift, the formation of the Antarctic Circumpolar Current blocked intrusions of warm tropical waters that warmed Antarctic and initiated the Antarctic Refrigerator Effect. Cold polar regions are a natural result of inadequate solar radiation. Reduced forcing from diminished levels of CO2 is not required to explain global cooling. The resulting formation of Antarctic sea ice expelled colder, salty waters that filled the abyss and began cooling the deep oceans. After 30+ million years of cooling, 2 to 3 million years ago, colder ocean waters eventually upwelled in the mid latitudes along the west coasts of major continents as well as along the equator. The resulting global cooling, allowed the growth of Arctic ice caps, glaciers and sea ice. The Antarctic Circumpolar Current also increased global upwelling and the efficiency of the biological pump. Decreases in atmospheric CO2 are associated with reductions in populations of CO2 producing coccolithophorids along with increasing populations of diatoms that pumped CO2 to depth. If the Antarctic Refrigeration Effect can account for the changes in global temperatures, it suggests the global sensitivity to varying levels of CO2 is relatively insignificant.

Natural Cycles of Polar Sea Ice: The Arctic Iris Effect

The Arctic Iris Effect, Dansgaard-Oeschger Events, 

and Climate Model Shortcomings. 

Lesson from Climate Past - part 1.

Dansgaard Oeschger Events and the Arctic Iris Effect

During the last Ice Age, Greenland’s average temperatures dramatically rose on average every 1500 years by 10°C +/- 5°C in a just matter of one or two decades, and then more gradually cooled as illustrated in Figure 1 below (8 of the 25 D-O events are numbered in red on upper graph; from Ahn 2008). These extreme temperature fluctuations between cold “stadials” that lasted about a thousand years and warm “interstadials” lasting decades are dubbed Dansgaard-Oeschger events (D-O events). These rapid temperature fluctuations not only rivaled the 100,000‑year fluctuations between maximum glacial cold and warm interglacial temperatures but D‑O warm events coincided with expanding Eurasian forests (Sánchez Goñi 2008, Jimenez-Moreno 2009), northward shifts of subtropical currents along the California coast (Hendy 2000), and shifts in belts of precipitation in northern South America (Peterson 2001).

Dansgaard Oeschger Events

Just 25 years ago most climate researchers were hesitant to accept initial Greenland ice core evidence suggesting such abrupt D‑O warming events (Dansgaard 1985). But as other Greenland ice cores verified their reality, it was clear that the only mechanism realistically capable of producing such abrupt warming was the sudden removal of insulating sea ice that allowed ventilation of heat previously stored in the Arctic as Dansgaard (1985) had first proposed. Still that begged the question ‘what caused the sudden loss of insulating sea ice’?

Changes in CO2 concentration are unlikely to have had much impact on D‑O events (3^rd graph from the top in Figure 1). CO2 concentrations did fluctuate by about 20 ppm during a third of the D-O events (red numbers), but could contribute directly to no more than 0.4°C to only 30% of the largest warming events.  In contrast during 68% of the other D-O events (not numbered), abrupt warming occurred while CO2 was declining.  Thus rapid warming and cooling seems independent of any CO2 forcing.

Abrupt D‑O warming and cooling suggested to researchers (Broecker 1985) that the Atlantic Meridonal Overturning Circulation (AMOC) turned “on” and “off”. Based on the misleading belief in the existence of a simplistic “ocean conveyor belt” (Wunsch 2007), researchers incorrectly interpreted a lack of deep-water formation as evidence of a lack of warm water flowing into the Arctic. However based on increasing proxy evidence (Rasmussen 2004, Ezat 2014), it is now understood that the inflow of warm Atlantic Waters never “shut off” but continued to enter the Arctic and warmed the subsurface layers. As seen in Figure 2  (from Itkin 2015) the upper layer of fresh water and the halocline insulate the warm Atlantic water from the overlying ice.  Together the thick sea ice and polar mixed layer simply “turn off“ any heat flux from the ocean to the air, thus maintaining cold stadial air temperatures. Furthermore if the salty Atlantic Water cannot be cooled by the cold Arctic air, then North Atlantic Deep Water is shut off as well.

Basic Vertical Structure of Arctic Ocean

Although climate models have failed to simulate D‑O events, models were manipulated to shut off poleward heat transport by prescribing ad hoc floods of freshwater. As long as freshwater “hosing” was applied, the models prevented the cooling and sinking of North Atlantic waters, which shutoff the deep water formation and thus “ocean conveyor belt” resulting in contrived cooling.  That interpretation became the reigning paradigm and researchers began searching for evidence of a flood of freshwater, while nearly every model engaged in “hosing” experiments to explain abrupt climate change. But evidence of the required freshwater flooding has yet to be found and a growing wealth of proxy evidence suggested there was as much freshwater during stadials as there was during interstadials. Even the notion of freshwater floods from an armada of melting icebergs was not consistent with the timing of D‑O events (Barker 2015). Freshwater shutdown of the Atlantic Meridonal Overturning Circulation is most likely just a figment of the models’ configuration.

Other researchers suggested drivers of past and present rapid temperature change were likely to be very similar (Bond 2001, 2005), and recent findings are now supporting that notion. More recent explanatory hypotheses for D‑O events are gaining widespread critical acceptance and do not require any massive floods of freshwater nor a shutdown of the AMOC (Rasmussen 2004, Li 2010, Peterson 2013, Dokken 2013, Hewitt 2015). When sea ice prevents heat ventilation, the inflow of warm and dense Atlantic Waters continues to store heat in the subsurface layers. As heat accumulated, the warm Atlantic Waters became more buoyant, upwelled and melted the insulating ice cover. The loss of an insulating ice cover “turns on” the heat flux causing a dramatic rise in surface temperatures to begin the D‑O interstadial.  Although details of hypothesized D‑O mechanisms vary slightly, they all agree on the ability of growing and shrinking sea ice to affect the heating and cooling of the northern hemisphere. I refer to this sea ice control of heat ventilation the Arctic Iris Effect.

The signature of an Arctic Iris Effect is the opposing temperature trends in the ocean versus atmosphere: when ice is removed, warmer air temperatures coincide with cooler ocean temperatures. When ice returns cooler air temperatures coincide with a warmer ocean. The thicker the sea ice, as during the last Ice Age, the longer the period between ventilations such as the D‑O events. Thick sea ice is less sensitive to small changes in insolation and/or natural variations of inflowing Atlantic Waters. As discussed in Hewitt 2015 decreases in the freshwater layer that separates sea ice from the warm Atlantic Waters are also likely critical contributors to D‑O events. For example as the Laurentide Ice Sheet grew, sea levels fell shutting of the inflow of fresher Pacific water through the Bering Strait, coinciding with an increased frequency between D‑O events from 8 thousand to 1.5 thousand years.

Peterson 2013 suggested that in addition to thick multiyear sea ice, ice shelves were critical for maintaining the longer cold stadials by better resisting small oscillations of increased inflow of Atlantic Water. Likewise with the current reduction of Arctic ice shelves and reduced multiyear sea ice during our present interglacial, much smaller changes in insolation and/or Atlantic inflow could more easily initiate ventilation events. With smaller time spans between each ventilation event, less heat accumulates and warm spikes are more muted (1°C to 2°C) compared to 10°C +/- 5°C during the D‑O interstadials. Over the past 6000 years, decades of rapid ice loss resulted in 2°C to 6°C air temperatures warmer than today quickly followed by centuries of colder temperatures and more sea ice (Mudie 2005).

The 20^th century ventilation events produced only a 1°C to 2°C increase yet the signature of the Arctic Iris Effect is still observed.  In 2001, Dr. Vinje of the Norwegian Polar Institute reported on the opposing temperature effects as ice retreated in the Nordic Seas. Between 1850 and 1900 there was a rapid warming of 0.5°C ocean temperatures between 1850 and 1900 with very little change in atmospheric temperature. Then they reported, “The warming event during the first decades of this century is characterized by a significant decrease in the Nordic Seas’ April ice extent, an increase of ~3°C in the Arctic surface winter temperature, averaged over the circumpolar zone between 72.5° and 87.5°N, and an increase in the Spitsbergen mean winter temperature of as much ~9°C. During this warming event the temperature in the ocean was lower than normal.

An increasing preponderance of positive ice extent anomalies, with an optimum in the 1960s, is observed during the period 1949–66, concurrent with a cooling in the circumpolar zone of ~1°C, a fall in the Spitsbergen mean winter temperature of ~3°C, and an increase in the mean winter air pressure in the western Barents Sea of ~6 hPa. During this cooling event the temperature in the ocean was higher than normal.” [Emphasis Added]

Similarly the most recent Arctic warming again reveals the fingerprint of the Arctic Iris Effect. There was no atmospheric warming in Arctic when there was an insulating cover of multiyear sea ice. Measurements between 1950 and 1990 reported a cooling Arctic atmosphere prompting researchers to publish, “Absence Of Evidence For Greenhouse Warming Over The Arctic Ocean In The Past 40 Years”.  They concluded, “This discrepancy suggests that present climate models do not adequately incorporate the physical processes that affect the Polar Regions.”

Abruptly rapid Arctic warming began in the 1990s with an initial loss and thinning of Arctic sea ice when the Arctic Oscillation’s shifted wind directions and below‑freezing winds from Siberia pushed multiyear ice out of the Arctic. Rigor 2002 correctly pointed out, “One could ask, did the warming of SAT [Surface Air Temperatures] act to thin and decrease the area of sea ice, or did the thinner and less expansive area of sea ice allow more heat to flux from the ocean to warm the atmosphere?” They concluded, “Intuitively, one might have expected the warming trends in SAT to cause the thinning of sea ice, but the results presented in this study imply the inverse causality; that is, that the thinning ice has warmed SAT by increasing the heat flux from the ocean.” [Emphasis Added] That conclusion has been further supported by recent analyses of ocean heat content by Wunsch and Heimbach 2014, two of the world’s premiere ocean scientists from Harvard and MIT. They reported the deep oceans are cooling suggesting the oceans and atmosphere are still not in equilibrium and oceans are still ventilating heat from below 2000 meters that was stored long ago.  Also in their map illustrating changes in the upper 700 meters of the world’s oceans (their Figure shown below), we see the entire Arctic Ocean has cooled between 1993 and 2011, as would be expected from the Arctic Iris Effect. Keep in mind that the warm layer of Atlantic water on average occupies the depths between 100 and 900 meters.

Change in upper 700  meters Ocean Heat Content 1993 t0 2011

The Earth’s Energy Budget

The Earth’s energy budget depends on a balance between absorbed solar radiation and outgoing infrared radiation. While some atmospheric scientists have focused on a possible energy imbalance created by 2 watts/m² generated by rising CO2, widespread regions of the ocean absorb and ventilate over 200 watts/m² of heat each year. As illustrated in Figure 3 (from Liang 2015), the oceans absorb heat (blue shades, in watts/m2) along the equator and over the upwelling zones along the continents’ west coast. Intense tropical insolation and evaporation creates warm dense salty waters that sink below the surface storing heat at depth. Changes in insolation, tropical cloud cover, and ocean oscillations like El Nino affect how much heat the oceans absorb or ventilate. Excess heat absorbed in the tropics is transported poleward. To gain a proper perspective on the importance of heat transport from the tropics to the poles, currently Polar Regions average 30°C colder than the equator. If there was no heat transport, the poles would be 110°C colder than the tropics (Gill 1982, Lozier 2012).

On average, the greatest ventilation of ocean heat happens where heat transportation is most concentrated: along the east coast of Asia over the Kuroshio Current and along east coast of North America along the Gulf Stream. Additionally large amounts of heat are also ventilated over Arctic’s Nordic Seas region, a focal point of the Arctic Iris Effect. A comparison of the temperature changes at varying ice core locations from southeast to northwest Greenland, points to this North Atlantic region as the main source of heat ventilated during each D‑O event (Buizert 2014). Likewise modeling work (Li 2010) shows that reduced ice extent in this region exerts the greatest impact on Greenland temperatures and snow accumulation rates. And it is in this same region that Vinje 2001 reports the greatest reduction in ice cover coinciding with the rapid changes in Greenland’s instrumental data. While CO2 warming would predict the greatest rate of Greenland warming in the most recent decades, the Arctic Iris effect would predict a greater rate of warming in the 1920s because thick sea ice from the Little Ice Age would have caused a greater accumulation of heat. Indeed Chylek 2005 reported, “the rate of warming in 1920–1930 was about 50% higher than that in 1995–2005.”

 

Global Ocean Heat Flux (blue: heat enters ocean, red heat exits ocean) Liang 2015

Climate Model Shortcomings

In 2008 leading climate scientists at the University of East Anglia’s Climatic Research Unit published Attribution Of Polar Warming To Human Influence.  As seen in their graph below, their models completely failed to account for the 2°C Arctic warming event observed from 1920 to the 1940s, (illustrated by the black line labeled “Obs” for observed).  This was a warming event that climate scientists called “the most spectacular event of the century” (Bengtsson 2004). Their modeled results of natural climate change grossly underestimated the 40s peak warming by ~0.8° C, and simulated a flat temperature trend throughout the 20^th century as illustrated by the blue line labeled “NAT” for natural. More striking when the models added CO2 and sulfates, the modeled results (red line labeled all) cooled the observed warming event further. Despite their failure to model natural events they concluded, “We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone, and are directly attributable to human influence.”

However their results only demonstrated that their models failed to account for natural climate change, the Arctic Iris Effect and ventilation of ocean heat during the 1930s and 40s. By all accounts the recent warming of the 1990s and 2000 was likewise a ventilation event that also cooled the upper layers of the Arctic Ocean. The failure to model ventilated heat events led to incorrectly attributing that warming to increasing concentrations of CO2.  That failed modeling further led to explanations that reduced albedo effect allowed greater absorption of summer insolation, warming the Arctic Ocean and amplifying temperatures. But observations show the ocean has cooled.  Like the 40s peak, it is likely 1990s/2000s ventilation similarly contributed a minimum of ~0.8° C to the recent rise in Arctic temperatures, and probably much more as the greater reduction in sea ice extent has allowed for much more ventilation.

Failed Climate Model and Warm Arctic Events

If climates models are correctly configured, they should be able to reproduce both D‑O events and the 1940s ventilation events. We don’t expect model perfection, but turning a massive warming event into a below average cool period is unacceptable.  When the modeling community simulates the Arctic Iris Effect more accurately, only then will their attribution of polar warming to human vs. natural factors be trustworthy! Until then all the natural factors - lower insolation with reduced Atlantic inflow, cooler oceans, negative North Atlantic Oscillation, and increasing multiyear ice – all suggest the current ventilation event will soon come to a close. But the return to cooler surface temperatures and more sea ice has always been much slower than the abrupt warming. When sea ice is reduced, the winds are suddenly able to mix the ocean’s fresher upper layer with the saltier lower Atlantic Waters disrupting the halocline. But once the halocline and upper layers of freshwater are restored, the cooling is rapid.  

In contrast, those who attribute Arctic warming to rising CO2 predict a continued sea ice death spiral. And those who also suggest global warming is slowing down the poleward flow of Atlantic Water, also argue CO2 warming will offset any cooling effects of that slowdown (Rhamstorf and Mann 2015). Within the next 2 decades, nature should demonstrate how well these competing models and competing interpretations extrapolate into the future. Good scientists always embrace 2 or more working hypotheses. But with the politicization of science, I sincerely doubt President Obama is travelling to the Arctic to advise the world to be good scientists!