350 ppm CO2 The Target

ISIS Report 09/09/09

350 ppm CO2 The Target
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Reducing present atmospheric CO2 to 350 ppm is needed to
avert irreversible climate catastrophe, top climate
scientists say Dr. Mae-Wan Ho

Rajendra Pachauri, United Nation’s top climate scientist and
head of the Intergovernmental Panel on Climate Change
(IPCC), took everyone by surprise when he said that the
target to aim for is 350 parts per million (ppm) CO2 in the
atmosphere, bearing in mind that we now have 385 ppm.

The IPCC produces an authoritative assessment of climate
science every five years. Its last report in 2007 helped set
the target of 450 ppm that many environmental groups and
national governments have adopted as their goal for the
Copenhagen negotiation this December.

But 450 ppm is out of date. When Jim Hansen from NASA
Goddard Institute for Space Studies, New York, in the US and
other scientists looked at phenomena such as how rapidly
polar ice has been melting in summer [1], they produced a
convincing demonstrating that 350 ppm is the bottom line.
“But it's been hard to get that news out to the powers that
be. So today it comes as enormous and welcome news that
Pachauri, from his New Delhi office, said that 350 was the
number,” [2] wrote Bill McKibben, prominent author and
environmentalist.

350 ppm needed to avert “irreversible catastrophic effects”

Concern about global warming due to greenhouse gases (GHGs)
led to the United Nations Framework Convention on Climate
Change [3] that has the objective of stabilizing GHGs in the
atmosphere at a level preventing “dangerous anthropogenic
interference with the climate system.”

In its 2007 report [4], the IPCC estimates that global
warming of more than 2-3 °C may be dangerous. The European
Union adopted 2 °C above pre-industrial global temperature
as a goal. This and other considerations led to the 450 ppm
CO2 maximum target.

But Hansen and colleagues [5] point out that IPCC climate
models are inadequate, as they include only fast feedback
processes, which gives ~ 3 °C warming for doubled CO2, a
figure referred to as ‘climate sensitivity’. Instead, the
more realistic climate sensitivity that includes also slow
feedback processes is ~6 °C for doubled CO2. The earth’s
history shows that this doubling of CO2 covers the range of
climate states between glacial conditions and ice-free
Antarctica.

The decrease from a high atmospheric CO2 was the main cause
of a cooling trend that began 50 million years ago, when the
planet remained nearly ice-free until CO2 fell to 450 ± 100
ppm. Hansen’s team point out that unless we have prompt
policy changes, the critical level of atmospheric CO2 will
be passed in the opposite direction - glacial to ice free -
within decades. “Paleoclimate evidence and ongoing climate
change suggest that CO2 will need to be reduced from its
current 385 ppm to at most 350 ppm, but likely less than
that.” They wrote.

They suggest this target may be achievable by phasing out
coal use, except where CO2 is captured; and adopting
agricultural and forestry practices that sequester carbon.

If the present overshoot of this target CO2 is not brief,
there is a possibility of seeding “irreversible catastrophic
effects”.

Read the rest of this report here
http://www.i-sis.org.uk/350ppm_CO2_the_Target.php

Or read other articles about climate change here
http://www.i-sis.org.uk/climateglobalwarming.php