This is a rather important issue
and what we have is geological evidence whose level of resolution is in the order
of ten millennia at a crack. Then we
assume some form of continuity and end up producing nonsense. I am not sure what these long periods of
climates been warmer by 2 to 3 degrees actually mean, but the one mechanism
able to do this is the positioning of a polar ice cap that survives. The actual cooling range also conforms to our
expectations.
It needs to be remembered that
Ice Age Earth was the result of two fully emplaced polar ice caps and the
blockage of a substantial part of the equatorial current. One could hardly design a worse situation. This ended by preserving the South Polar Cap
while engaging the Gulf Stream to end the
North Polar Cap. It is my conjecture
that this was done deliberately for this exact purpose (it was really too good
to be an accident) and that the resultant Holocene is good for millions of year
if not until the Pacific itself is subsumed.
Of course, current scholarship
prefers to accept the curious idea that the Ice Age penetrated in full into the
lower latitudes, when that naturally is impossible without creating Ice Ball
Earth. In fact all the main arguments
against an Ice Age from the nineteenth century never were resolved and have
simply been forgotten in the face of overwhelming evidence of simple
existence. The fact is that simply
rotating the crust so that the North Pole is at thirty degrees south in Hudson
Bay makes all those nineteenth century objections and a lot more besides simply
disappear because the entirety if the purported Ice Age is then actually in the
appropriate fifteen degrees of the poles is and was Antarctica.
It is reasonable that a large
land mass passing through a pole would accumulate an ice cap that may well be
vulnerable to melt outs. This would be
able to adjust temperatures by the expected range on the geological time scale
proposed. It is useful to think of such
caps as the temperature control device that can be adjusted by many other
possible events from magma flows elsewhere to asteroid impacts anywhere.
Ancient 'hyperthermals' guide to anticipated climate changes
Bursts of intense global warming that have lasted tens of thousands of
years have taken place more frequently throughout history than previously
believed, according to researchers in the US
##
In a paper published in Nature, researchers from the Scripps
Institution of Oceanography at the University of California San Diego and
colleagues from the UK, Germany and Spain, report that releases of carbon
dioxide sequestered in the deep oceans were the most likely trigger of these
ancient "hyperthermal" events.
Most of the events raised average global temperatures between 2 and
3 °C, an amount comparable to current conservative estimates of how much
temperatures are expected to rise in coming decades as a consequence of
anthropogenic global warming. Most hyperthermals lasted about 40,000 years
before temperatures returned to normal.
"These hyperthermals seem not to have been rare events," says
Richard Norris from Scripps. "Hence there are lots of ancient examples of
global warming on a scale broadly like the expected future warming. We can use
these events to examine the impact of global change on marine ecosystems,
climate and ocean circulation."
The hyperthermals took place roughly every 400,000 years during
a warm period of Earth's history that prevailed some 50 million years ago.
The strongest of them coincided with an event known as the Paleocene–Eocene
Thermal Maximum, the transition between two geologic epochs in which global
temperatures rose between 4 and 7 °C and needed 200,000 years to
return to historical norms. The events stopped taking place around
40 million years ago, when the planet entered a cooling phase. No warming
events of the magnitude of these hyperthermals have been detected in the
geological record since then.
Phil Sexton, a former student of Norris' now at the Open University,
UK, led the analysis of sediment cores collected off the South American coast.
In the cores, evidence of the warm periods presented itself in bands of grey
sediment layered within otherwise pale-greenish mud. The grey sediment
contained increased amounts of clay left after the calcareous shells of
microscopic organisms were dissolved on the sea floor. These clay-rich
intervals are consistent with ocean acidification episodes that would have been
triggered by large-scale releases of carbon dioxide. Large influxes of carbon
dioxide change the chemistry of seawater by producing greater amounts of
carbonic acid in the oceans.
The authors concluded that a release of carbon dioxide from the deep
oceans was a more likely cause of the hyperthermals than other triggering
events that have been hypothesized. The regularity of the hyperthermals and
relatively warm ocean temperatures of the period makes them less likely to have
been caused by events such as large melt-offs of methane hydrates, terrestrial
burning of peat or even proposed cometary impacts. The hyperthermals could have
been set in motion by a build-up of carbon dioxide in the deep oceans caused by
slowing or stopping of circulation in ocean
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