Six scientists from some of the leading scientific institutions in the
United States have issued what amounts to an unambiguous warning to the
world: civilisation itself is threatened by global warming.
They also implicitly criticise the UN's Intergovernmental Panel on
Climate Change (IPCC) for underestimating the scale of sea-level rises
this century as a result of melting glaciers and polar ice sheets.
Instead of sea levels rising by about 40 centimetres, as the IPCC
predicts in one of its computer forecasts, the true rise might be as
great as several metres by 2100. That is why, they say, planet Earth
today is in "imminent peril".
In a densely referenced scientific paper published in the
Philosophical Transactions of the Royal Society A some of the world's
leading climate researchers describe in detail why they believe that
humanity can no longer afford to ignore the "gravest threat" of climate
change.
"Recent greenhouse gas emissions place the Earth perilously close to
dramatic climate change that could run out of control, with great
dangers for humans and other creatures," the scientists say. Only
intense efforts to curb man-made emissions of carbon dioxide emissions
and other greenhouse gases can keep the climate within or near the
range of the past one million years, they add.
The researchers were led by James Hansen, the director of Nasa's
Goddard Institute for Space Studies, who was the first scientist to
warn the US Congress about global warming.
The other scientists were Makiko Sato, Pushker Kharecha and Gary
Russell, also of the Goddard Institute, David Lea of the University of
California, Santa Barbara, and Mark Siddall of the Lamont-Doherty Earth
Observatory at Columbia University in New York.
In their 29-page paper, "Climate Change and trace gases", the
scientists frequently stray from the non-emotional language of science
to emphasise the scale of the problems and dangers posed by climate
change.
In an email to The Independent, Dr Hansen said: "In my opinion,
among our papers this one probably does the best job of making clear
that the Earth is getting perilously close to climate changes that
could run out of our control."
The unnatural "forcing" of the climate as a result of man-made
emissions of carbon dioxide and other greenhouse gases threatens to
generate a "flip" in the climate that could "spark a cataclysm" in the
massive ice sheets of Antarctica and Greenland, the scientists write.
Dramatic flips in the climate have occurred in the past but none has
happened since the development of complex human societies and
civilisation, which are unlikely to survive the same sort of
environmental changes if they occurred now.
"Civilisation developed, and constructed extensive infrastructure,
during a period of unusual climate stability, the Holocene, now almost
12,000 years in duration. That period is about to end," the scientists
warn. Humanity cannot afford to burn the Earth's remaining underground
reserves of fossil fuel. "To do so would guarantee dramatic climate
change, yielding a different planet from the one on which civilisation
developed and for which extensive physical infrastructure has been
built," they say.
Dr Hansen said we have about 10 years to put into effect the
draconian measures needed to curb CO2 emissions quickly enough to avert
a dangerous rise in global temperature. Otherwise, the extra heat could
trigger the rapid melting of polar ice sheets, made far worse by the
"albedo flip" - when the sunlight reflected by white ice is suddenly
absorbed as ice melts to become the dark surface of open water.
The glaciers and ice sheets of Greenland in the northern hemisphere,
and the western Antarctic ice sheet in the south, both show signs of
the rapid changes predicted with rising temperatures. "
The albedo flip property of ice/water provides a trigger mechanism.
If the trigger mechanism is engaged long enough, multiple dynamical
feedbacks will cause ice sheet collapse," the scientists say. "We argue
that the required persistence for this trigger mechanism is at most a
century, probably less."
The latest assessment of the IPCC published earlier this year
predicts little or no contribution to 21st century sea level from
Greenland or Antarctica, but the six scientists dispute this
interpretation. "The IPCC analyses and projections do not well account
for the nonlinear physics of wet ice sheet disintegration, ice streams
and eroding ice shelves, nor are they consistent with the palaeoclimate
evidence we have presented for the absence of discernible lag between
ice sheet forcing and sea-level rise," the scientists say.
Their study looked back over more than 400,000 years of climate
records from deep ice cores and found evidence to suggest that rapid
climate change over a period of centuries, or even decades, have in the
past occurred once the world began to heat up and ice sheets started
melting. It is not possible to assess the dangerous level of man-made
greenhouse gases.
"However, it is much lower than has commonly been assumed. If we
have not already passed the dangerous level, the energy infrastructure
in place ensures that we will pass it within several decades," the
scientists say in their findings.
"We conclude that a feasible strategy for planetary rescue almost
surely requires a means of extracting [greenhouse gases] from the air."
Source: http://environment.independent.co.uk/climate_change/article2675747.ece
(Thanx Overtone).