by Tim Radford, Climate News Network, December 2, 2013
Countries round the world have pledged to try and limit the average
global temperature rise to 2 °C above pre industrial figures. That’s way
too high and would threaten major dislocations for civilization say a
group of prominent scientists.
London, 3 December
2013 – Governments have set the wrong target to limit climate change. The
goal at present – to limit global warming to a maximum of 2 °C higher
than the average for most of human history – “would have consequences
that can be described as disastrous,” say 18 scientists in a review
paper in the journal PLOS One.
With a 2 °C increase, “sea level rise of several meters could be
expected,” they say. “Increased climate extremes, already apparent at
0.8 °C warming, would be more severe. Coral reefs and associated species,
already stressed with current conditions, would be decimated by
increased acidification, temperature and sea level rise."
The paper’s lead author is James Hansen, now at Columbia University, New
York, and the former NASA scientist who in 1988 put global warming on
the world’s front pages by telling a US government committee that “It's
time to stop waffling so much and say the evidence is pretty strong that
the greenhouse effect is here.”
Hansen’s fellow authors include the economist Jeffrey Sachs of Columbia
University and the biologist Camille Parmesan, of the University of
Plymouth in the UK and the University of Texas at Austin, USA.
Their argument is that humanity and nature –“the modern world as we
know it” – is adapted to what scientists call the Holocene climate that
has existed for more than 10,000 years – since the end of the Ice Age,
the beginnings of agriculture and the first settlement of the cities.
Warming of 1 °C relative to 1880–1920 keeps global temperature close to
the Holocene range, but warming of 2°C, could cause “major dislocations
for civilization.”
The scientists study, uncompromisingly entitled “Assessing ‘dangerous
climate change’: required reduction of carbon emissions to protect young
people, future generations and nature” differs from many such climate
analyses because it sets out its argument with remarkable directness and
clarity, and serves as a useful briefing document for anyone –
politicians, journalists and lay audiences – anxious to better
understand the machinery of climate, and the forces that seem to be
about to dictate climate change.
Its critics will point out that it is also remarkably short on the usual
circumlocutions, caveats, disclaimers and equivocations that tend to
characterise most scientific papers. Hansen and his co-authors are
however quite open about the major areas of uncertainty: their implicit
argument is that if the worst outcomes turn out to be true, the
consequences for humankind could be catastrophic.
The scientists case is that most political debate addresses the
questions of reducing greenhouse gas emissions, but does not and perhaps
cannot factor in the all potentially dangerous unknowns – the slow
feedbacks that will follow the thawing of the Arctic, the release of
frozen reserves of methane and carbon dioxide in the permafrost, and the
melting of polar ice into the oceans. They point out that 170 nations
have agreed on the need to limit fossil fuel emissions to avoid
dangerous human-made climate change.
“However the stark reality is that global emissions have accelerated,
and new efforts are underway to massively expand fossil fuel extractions
by drilling to increasing ocean depths and into the Arctic, squeezing
oil from tar sands and tar shale, hydro-fracking to expand extraction of
natural gas, developing exploitation of methane hydrates and mining of
coal via mountain-top removal and mechanised long wall-mining.”
The scientists argue that swift and drastic action to limit global
greenhouse gas emissions and contain warming to around 1 °C would have
two useful consequences. One is that it would not be far from the
climate variations experienced as normal during the last 10,000 years,
and secondly that it would make it more likely that the biosphere, and
the soil, would be able to sequester a substantial proportion of the
carbon dioxide released by human industrial civilisation.
Trees are, in essence, captive carbon dioxide. But the warmer the world
becomes, the more likely it is that existing forests – the Amazon, for
example – will start to release more CO2 than they absorb, making the
planet progressively even warmer.
Therefore the scientists make a case for limiting overall global carbon
emissions to 500 gigatonnes rather than the 1,000 billion tonnes in the
2 °C rise scenario.
“Although there is merit in simply chronicling what is happening, there
is still opportunity for humanity to exercise free will,” says Hansen.
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