"If
you look at the fossil record, it is just littered with dead bodies
from past catastrophes," observes University of Washington
paleontologist Peter Ward. Ward says that only one extinction in
Earth's past was caused by an asteroid impact – the event 65 million
years ago that ended the age of the dinosaurs. All the rest, he claims,
were caused by global warming.
Ward’s Under a Green Sky explores extinctions in Earth's past and predicts extinctions to come in the future.
Ward
demonstrates that the ancient past is not just of academic concern.
Everyone has heard about how an asteroid did in the dinosaurs, and NASA
and other agencies now track Near Earth objects. Unfortunately, we may
not be protecting ourselves against the likeliest cause of our species’
demise. Ward explains how those extinctions happened, and then applies
those chilling lessons to the modern day: expect drought, superstorms,
poison–belching oceans, mass extinction of much life, and sickly green
skies.
The significant points Ward stresses are geologically
rapid climate change has been the underlying cause of most great
“extinction” events. Those events have been, observed Harvard
evolutionary biologist Stephen Gould, major drivers of evolution.
Drastic climate change has not always been gradual; there is solid
empirical evidence of catastrophic warming events taking place in
centuries, perhaps even decades. The impact of atmospheric warming is
most potent in its modification of ocean chemistry and of circulating
currents; warming inevitably leads to non-mixing anoxic dead seas. We
are already in the middle, not the beginning, of an anthropogenic
global warming, caused by agriculture and deforestation, which began
some 10,000 years ago but which is now accelerating exponentially;
though the earliest wave of anthropogenic warming has been stabilizing
and beneficial to human development, it appears to have the potential
for catastrophic effects within a lifetime or two.
Looking
at the ancient evidence, Ward notes that ice caps began to shrink.
“Melting all the ice caps causes a 75-meter increase in sea level will
remove every coastal city on our planet.” It will also cover earth’s
most productive farmland, the author warns, adding, “It will happen if
we do not somehow control CO2 rise in the atmosphere.”
A new analysis of the geological record of
the Earth’s sea level, carried out by scientists at Princeton and
Harvard universities supports Ward using a novel statistical approach that reveals the
planet’s polar ice sheets are vulnerable to large-scale melting even
under moderate global warming scenarios. Such melting would lead to a
large and relatively rapid rise in global sea level.
According to the analysis, an additional 2 degrees of global warming
could commit the planet to 6 to 9 meters (20 to 30 feet) of long-term
sea level rise. This rise would inundate low-lying coastal areas where
hundreds of millions of people now reside. It would permanently
submerge New Orleans and other parts of southern Louisiana, much of
southern Florida and other parts of the U.S. East Coast, much of
Bangladesh, and most of the Netherlands, unless unprecedented and
expensive coastal protection were undertaken. And while the
researchers’ findings indicate that such a rise would likely take
centuries to complete, if emissions of greenhouse gases are not abated,
the planet could be committed during this century to a level of warming
sufficient to trigger this outcome.
The last interglacial stage
provides a historical analog for futures with a fairly moderate amount
of warming; the high sea levels during the stage suggest that
significant chunks of major ice sheets could disappear over a period of
centuries in such futures.
Previous geological studies of sea
level benchmarks such as coral reefs and beaches had shown that, at
many localities, local sea levels during the last interglacial stage
were higher than today. But local sea levels differ from those in this
earlier stage; one major contributing factor is that the changing
masses of the ice sheets alter the planet’s gravitational field and
deform the solid Earth. As a consequence, inferring global sea level
from local geological sea level markers requires a geographically broad
data set, a model of the physics of sea level, and a means to integrate
the two. The study’s authors provide all three, integrating the data
and the physics with a statistical approach that allows them to assess
the probability distribution of past global sea level and its rate of
change.
The findings indicate that sea level during the last
interglacial stage rose for centuries at least two to three times
faster than the recent rate, and that both the Greenland and West
Antarctic ice sheet likely shrank significantly and made important
contributions to sea level rise. However, the relative timing of
temperature change and sea level change during the last interglacial
stage is fairly uncertain, so it is not possible to infer from the
analysis how long an exposure to peak temperatures during this stage
was needed to commit the planet to peak sea levels.
A similar
study by a team of scientists from Bristol, Cardiff and Texas A&M
universities braved the lions and hyenas of a small East African
village to extract microfossils from rocks which have revealed the
level of CO2 in the Earth's atmosphere at the time of the formation of
the ice-cap. New carbon dioxide data confirm that formation of the
Antarctic ice-cap some 33.5 million years ago was due to declining
carbon dioxide in the atmosphere.
Professor Paul Pearson from
Cardiff University's School of Earth and Ocean Sciences, who led the
mission to the remote East Africa village of Stakishari said: "About 34
million years ago the Earth experienced a mysterious cooling trend.
Glaciers and small ice sheets developed in Antarctica, sea levels fell
and temperate forests began to displace tropical-type vegetation in
many areas.
"The period culminated in the rapid development of a
continental-scale ice sheet on Antarctica, which has been there ever
since. We therefore set out to establish whether there was a
substantial decline in atmospheric carbon dioxide levels as the
Antarctic ice sheet began to grow."
Co-author Dr Bridget Wade
from Texas A&M University Department of Geology and Geophysics
added: "This was the biggest climate switch since the extinction of the
dinosaurs 65 million years ago. Our study is the first to provide a
direct link between the establishment of an ice sheet on Antarctica and
atmospheric carbon dioxide levels and therefore confirms the
relationship between carbon dioxide levels in the atmosphere and global
climate."
Geologists have long speculated that the formation of
the Antarctic ice-cap was caused by a gradually diminishing natural
greenhouse effect. The study's findings, published in Nature online,
confirm that atmospheric CO2 started to decline about 34 million years
ago, during the period known to geologists as the Eocene - Oligocene
climate transition, and that the ice sheet began to form about 33.5
million years ago when CO2 in the atmosphere reached a tipping point of
around 760 parts per million.
The team mapped large expanses of
bush and wilderness and pieced together the underlying local rock
formations using occasional outcrops of rocks and stream beds.
Eventually they discovered sediments of the right age near a
traditional African village called Stakishari. By assembling a drilling
rig and extracting hundreds of meters of samples from under the ground
they were able to obtain exactly the piece of Earth’s history they had
been searching for.
Ward is encouraged that we are
beginning to make changes in their daily lives and demanding action
from their leaders -”that we are on a planet that has violent
convulsions, and that we humans are playing with nature in such a way
that we could recreate what were some really awful times in earth’s
history, that we really tinker with the earth’s atmosphere at our
peril.”
Posted by Casey Kazan from material provided by Princeton University and Bristol University
http://www.bris.ac.uk/news/2009/6546.html
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