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.