You think that they would get it
already. The principle driver of climate change over the long term is the
geometry of the continents and the resultant current systems and polar ice
caps.
I also allow short term events
such as a pass through Sirius every 200,000 years or so which drives a major
warming over two millennia or so.
We presently live in a world
managed by one Ice Cap, an Atlantic positioned to drive equatorial waters into
the Arctic and a resultant climate that is the
best for several millions of years and will last for millions of years or even
hundreds of millions of years in fine order.
The Atlantic is opening and the
Antarctic is going nowhere. That means
that until the Pacific closes, things will be good. This one additional reason I suspect that the
Pleistocene nonconformity was deliberate.
Next time we pass through Sirius
we will see the Antarctic Ice sheet hugely melt out and the global climate
become broadly tropical even into the Arctic . What will really happen is that the tropical
zone will simply expand hugely and displace the temperate zones.
We will survive it handily
although we will need to get used to 100 F and a hundred percent humidity. It obviously can be done.
Oceans played critical role in ancient global cooling
by Staff Writers
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 sedimentsto
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 theAntarctic 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 here.
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 thecurrent climate change,"
Katz said.
Katz is joined in the research by Benjamin Cramer of Theiss Research;
J.R. Toggweiler of Geophysical Fluid Dynamics Lab/NOAA; Chengjie Liu of
ExxonMobil Exploration Co.; Bridget Wade of University of Leeds; and Gar Esmay,
Kenneth Miller, Yair Rosenthal, and James Wright of Rutgers University.
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