The Earth today stands in imminent peril
...and nothing short of a planetary rescue will save it from the
environmental cataclysm of dangerous climate change. Those are not the words of
eco-warriors but the considered opinion of a group of eminent scientists
writing in a peer-reviewed scientific journal.
By Steve Connor, Science Editor
The Independent
Published: 19 June 2007
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."
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