A similar low and high arsenic content accompanied the coming and going
of global glaciations at around 0.7 billion years ago, which is when Earth first saw the appearance of complex life.
Pierrehumbert RT 2004: High levels of atmospheric carbon dioxide necessary for the termination
of global glaciation Nature 429, 646 - 649.
«In particular, this mechanism may have contributed to Earth's entry into a long period
of global glaciation around 700 million years ago, a theory known as the Snowball Earth hypothesis.»
Three areas of particular interest and debate are the «faint young Sun paradox,» the role of organisms in shaping Earth's atmosphere, and the possibility that Earth went through one or more «snowball» phases
of global glaciation.
Not exact matches
«In addition, this early phase
of evolutionary divergence appears to have preceded the extreme climate changes that led to Snowball Earth, a period marked by severe long - term
global glaciation that lasted from about 720 to 635 million years ago,» Dohrmann says.
So the fact that we have this very strong drying in the tropics during
glaciation would argue for a strong feedback
of water vapor concentration to the
global climate during glacial - interglacial cycles.»
The late Proterozoic — the time period beginning less than a billion years ago following this remarkable chapter
of sustained low levels
of oxygen — was strikingly different, marked by extreme climatic events manifest in
global - scale
glaciation, indications
of at least intervals
of modern - like oxygen abundances, and the emergence and diversification
of the earliest animals.
The current
global cycle
of glaciation dates to this period and might have been triggered by a transformation
of the world's ocean currents, which a slender rib
of land separating Atlantic and Pacific would naturally explain.
The new production circumstances
of Code Unknown gave him the space and budget to retry and perfect some
of the thematic strategies risked in the
glaciation trilogy, but it is the combination
of the fates
of semi-established African residents in Paris with those
of Romanians in the country illegally and begging in the streets that makes the film feel more
global in scope than his earlier work.
I'm a fish geneticist so I won't bother commenting on «paleo - ocean current - ology», but it seems to me that
glaciation would result in a reduction
of fresh water inputs to the North Atlantic (during the ice age) and would therefore be quite different from the mechanism in question (which is related to early phases
of global warming).
Without knowing the bigger picture (i.e having right
global model
of glaciations - deglaciations), the «local» responses may be misleading, especially for practical purposes.
The earth has had significant
Global Warming for some 20,000 years now... The only real argument is to the degree that mans activity has augmented that... We just came out
of one - point - five - million years
of continuous
glaciation with sheets
of two mile thick ice down past the 44th parallel... I will cheerfully deal with warming issues over that, any day...
Clearly Antarctic
glaciation was not part
of a
global event, but a regional one.
So what are you willing to do to prevent rapid cooling into the next
glaciation — rather than the lemming mantra
of global warming?
C: Datasets suggesting a drying environment at 2.5 Ma, shown by λ 18O from benthic foraminifera, a proxy for
global temperature, smoothed with a Gaussian window
of 200 ky; eustatic sea level; and magnetic susceptibility, a proxy for ice rafted debris and Northern Hemisphere
glaciation.
However, we know that severe and abrupt climate shifts
of global extent have occurred (infrequently) during
glaciations, and almost never during warmer interglacial periods such as the current Holocene.
The few degrees
of global temperature rise since the depths
of the Pleistocene
glaciation (say 18,000 ybp) can be seen as a short - term reversal
of a long - term cooling trend.
In 1974 when the Club
of Rome formulated it, the consensus was that
global cooling (due to dust and pollution from natural volcanic eruptions and from industry) was screening out sunlight, and we were in for runaway
glaciation and a new ice age.
Cenozoic evolution
of Antarctic
glaciation, the circum - Antarctic Ocean, and their impact on
global paleoceanography
In a paper «
Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation», Shakun et al. (Nature 2012) contend that rising temperature at the end
of the last Pleistocene
glaciation were preceded by increasing atmospheric CO2.
As far as CO2 «signatures» go, it is hard to verify that CO2 is having any warming, as in
Global Warming» impact and the black carbon associated with «the Social Cost
of Carbon» has a more easily verified impact which is to reduce snow fields which are the lead in to
glaciation.
In my search to be informed about all this
global warming and co2 concern I found the Orbital Variations in connection with the Stages
of Glaciation very interesting.