Dear Tom,
As I understand it, the "climate sensitivity", used by IPCC in their
models, concerns the global warming effect of a doubling of atmospheric
CO2 above the pre-industrial level. Critical to this is the CO2
behaviour over time - and Archer's work on the decay of an added pulse
is extremely relevant. I don't believe that the long tail, where a
proportion (about 25%) of the pulse lasts thousands of years, is taken
into account in IPCC models, which you and Ken have probably been
using.
Further to this lifetime issue is the positive feedback, which was
largely ignored by IPCC as it was difficult to model. The tipping
points in the Arctic, such as massive methane release, make nonsense of
the notion of climate sensitivity.
Thus I stick to my assertion that, if we were all to drop dead
tomorrow, global warming would continue - at least until well over the
proposed 2 degrees ceiling.
The message for Copenhagen is that emissions reduction, however
drastic, cannot avert disastrous global warming which would
threaten all our lives. We need such a stark message to shake
politicians and the media out of their state of near apathy towards
global warming.
We should then present the case for geoengineering intervention, and
explain that we need SRM geoengineering especially urgently to save the
Arctic sea ice, which could disappear much sooner than expected - even
just possibly within a couple of years.
Cheers,
John
---
Tom Wigley wrote:
Re C
cycle, no-one makes assumptions about the CO2 lifetime.
The C cycle operates on a range of time scales. These are determined
by the physics/chemistry/biology of the C cycle model. We are way
beyond simplistic "lifetime-based" C cycle models.
Tom.
++++++++++++++++++++
John Nissen wrote:
Dear Tom,
Let us first set aside considerations of tipping points in the Arctic,
and focus of the CO2 effect on temperature.
This is a fundamental question: which of us is right about the effect
of zero CO2 emissions! The whole basis of the forthcoming Copenhagen
meeting is that, if we reduce global CO2 emissions sufficiently, and
sufficiently quickly, then it will reduce global warming such as to
keep the temperature below a ceiling - suggested as 2 degrees below the
1900 temperature level by some, 1 degree below the 2000 level by
professor Jim Hansen (equivalent to 1.7 degrees below the 1900 level).
I query that whole basis.
You said your model is "consistent with the science of the AR4". Now,
when I looked at the models being used by IPCC and Hansen, it seemed
that they assumed a relatively short effective CO2 lifetime, somewhere
in the range 50-200 years. However effective lifetime of a proportion
of the excess CO2 (above pre-industrial 280 ppm level) is now thought
to be many thousands of years [1]. Indeed David Keith, in his talk to
us at the RGS on May 14th [2], emphasised that the effective half-life
of anthropogenic CO2 was many thousands of years - much longer than
nuclear waste!
There is certainly sufficient to continue a net forcing for global
warming, currently at 1.6 W/m-2.
So I just don't believe that reducing emissions can halt global
warming. I said so to professor Hansen when I met him very briefly
before a lecture, but he said he was sure that negative feedback would
cut in quickly. Where is this negative feedback coming from? There is
a small amount from increased infra-red heat radiation, as the average
global temperature increases. Against that, there is mounting positive
feedback, e.g. from increased water vapour (a greenhouse gas) and from
the "albedo effect" in polar regions.
So now if we bring in the Arctic, the melting of the Arctic sea ice
will add a globally-averaged forcing of between 0.5 and 1.5 W/m-2. If
then the massive amounts of methane, currently trapped in frozen
structures, start to get released, then we would have forcing quickly
climbing to many Watts/m-2, and we could be in for a warming event on a
par with the Paleocene/Eocene thermal maximum (PETM), 55.8 million
years ago [3]. That would be my scary "Back to Nature" scenario! So,
even if you are right about the effectiveness of emissions reduction,
it is academic if we do not cool the Arctic by geoengineering. Can you
at least support that message for Copenhagen?
Best wishes,
John
[1]
http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B3
According to Archer, some of the excess CO2 (fossil fuel component)
will be gradually absorbed by deep ocean over a few hundred years, but
the remaining 25% will last for many thousands of years. Here is his
model simulation of atmospheric CO_2 concentration for 40,000 years
following after a large CO_2 release from combustion of fossil fuels.
Different fractions of the released gas recover on different
timescales. Reproduced from /The Long Thaw/:
Unfortunately we are unable to provide accessible alternative text for
this. If you require assistance to access this image, or to obtain a
text description, please contact [email protected]
[2]
http://www.21stcenturychallenges.org/challenges/engineering-our-climate-is-there-a-role
-for-geoengineering/media-gallery/video/professor-david-keith/
[3] http://en.wikipedia.org/wiki/Paleocene-Eocene_Thermal_Maximum
Tom Wigley wrote:
John,
You are wrong. If we stop all emissions immediately, the warming
trend will stop and reverse. In the attached ms I set all emissions
to zero from 2021 onwards.
Tom.
+++++++++++++++++++++++
John Nissen wrote:
No, it's all wrong - about the CO2 being absorbed from the atmosphere
and the planet cooling. On the contrary, if we were all to drop dead
tomorrow, global warming would continue for thousands of years, as I
explain in the thread I started, about the GREAT LIE. There'd also be
an immediate warming spurt, as the sulphur aerosol pollution (which
has a cooling effect) would be quickly washed out of the atmosphere.
And,within a few decades, on top of the CO2 warming would be the
warming from methane as permafrost melted, and the sea level would rise
60-70 metres as Greenland and Antarctic ice sheets melted.
Thus, if we disappear, or just carry on as we are for that matter, the
Earth will continue tipping into a super-hot state, which probably
won't be habitable for humans, even at the poles. However it is
unlikely that the Earth will go the way of Venus, with the oceans
boiling away, if that's any comfort.
Cheers,
John
---
Alvia Gaskill wrote:
http://en.wikipedia.org/wiki/Aftermath:_Population_Zero
I recently saw the Nat. Geo program "Aftermath: Population Zero," one
of several hypothetical accounts of what the world would be like
without people. Not less people, no people. These seem to have been
inspired by the work of Alan Weisman, author of the book "The World
Without Us."
http://en.wikipedia.org/wiki/The_World_Without_Us
In addition to describing what would happen to domesticated animals and
pets left without humans to take care of them, the fate of
infrastructure is also presented. This particular program (there is
another one that has been turned into a series on the History Channel
called, appropriately enough, "Life After People"
http://en.wikipedia.org/wiki/Life_After_People ;
http://en.wikipedia.org/wiki/Life_After_People:_The_Series [for those
people still not depressed enough after watching the original
documentary]) also explores changes in the Earth's climate without its
number one interferent, us.
After 150 years, winters are colder than during the last days of humans
with greater snowfall, indicating declining GHG levels. It is stated
that the oceans will remove 13.5Gt of CO2 per year. Is this correct?
After 200 years, the excess CO2 from human emissions is completely
eliminated by plants and trees. Don't tell David Archer. Perhaps the
increase in plant growth will speed the removal. Or won't that matter?
After 500 years, forests return to the state they had 10,000 years
ago. I doubt that one, as that would have been at the tail end of the
ice age.
After 25,000 years, the interglacial is over, the ice sheets return and
erase NYC along with most of the areas wiped out before. Which raises
an interesting question for the geo haters. If it became apparent that
the interglacial was ending, would you be in favor of artificial means
of prolonging it to ensure the planet's habitability for billions of
humans? If you say no, then I think I'm going to propose to Nat. Geo
or History a new series, Life After YOU People!
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