Ken
I understand that methane concentrations are now about 1.8 parts per
million, still much less than those of CO2 but that methane accounts for
about one third of the warming of CO2. Would things change if there
were sudden large increases in the rate of methane release as suggested
by Semiletov and Shakhova?
Stephen
Emeritus Professor of Engineering Design
Institute for Energy Systems
School of Engineering
Mayfield Road
University of Edinburgh EH9 3JL
Scotland
Tel +44 131 650 5704
Mobile 07795 203 195
www.see.ed.ac.uk/~shs
On 21/02/2012 17:17, Ken Caldeira wrote:
The higher climate sensitivities (e.g. approaching 10 C per CO2
doubling) are highly unlikely for this century and, if such
sensitivities are real (which I also deem unlikely), likely they would
be the product of feedbacks occurring on timescales of thousands of
years (e.g. ice sheets).
The climate models include most of the feedbacks that occur on the
time scale of a century or less, and therefore likely reflect the
sensitivity that is most relevant to most people living this century
(e.g., about 3 C per CO2 doubling).
I could believe that Earth System Sensitivity (millennial scale) is
twice that of Charney Sensitivity (decadal scale).
-------------
At higher CO2 levels, due to diminished ocean CO2 uptake, each CO2
emissions contributes more to atmospheric CO2 increase, but each
increment of increase has less of a radiative effect. These two
effects largely cancel each other but not of course precisely. There
was a paper that went into this more carefully but I cannot put my
finger on it, having looked for it.
At the highest CO2 levels, you are of course right that essentially
all of the CO2 is partitioned into the atmosphere, but the radiative
effect will be small, so the tendency is towards decreasing radiative
forcing with each emission. But, before the radiative forcing from
each emission becomes negligible, we will be living inside of a toaster.
For an approximation that is close enough for policy purposes, you are
not far off if you assume that each CO2 emission this century produces
another increment of warming, where this warming takes a few decades
to manifest itself. The imperfection of the chemistry/physics
cancellation might be something like a 20% error this century
(although I have not recently gone through the numbers and cannot
fully attest to this).
On Tue, Feb 21, 2012 at 7:35 AM, Robert Chris <r.g.ch...@open.ac.uk
<mailto:r.g.ch...@open.ac.uk>> wrote:
Ken
Thanks for replying to my email. You were right. The Google Group
worked much quicker than I'd anticipated.
There's quite a lot of technical material here for a humble social
scientist to digest. On a quick scan the message I get is that the
forcing is logarithmic but climate sensitivity is linear because of
compensating feedbacks in the climate system. Although it does seem
to me that if the forcing is logarithmic there must come a point where
the absorptive capacity of the GHGs is so small that incremental
emissions will not produce any more global warming. Moreover, there
must be a point where the oceans are also largely saturated and take
up little more CO2. However, the point where climate sensitivity does
reduce to close to zero, might not be reached before we're all fried
and the oceans are nigh on dead. If that brief extrapolation makes
sense, has anyone attempted to estimate where those limits might be?
What has jumped out at me from these replies is the Wasdell paper. He
is highlighting the distinction between the Charney and ESS approaches
to the quantification of climate sensitivity. This is not an academic
peer-reviewed paper although he does refer to several but if he is
correct that climate sensitivity now looks like it might be closer to
10degC rather than 3degC, that should send alarm bells ringing that I
certainly don't hear. Is that because ESS is not yet sufficiently
robust for it to replace Charney; simply because the material has yet
to be published, or because even though CS might be three times higher
than previously thought, the time lag before the equilibrium is
reached is such that things won't warm up that much faster in the
short term and therefore no one's too concerned about it yet?
But if ESS does provide a more accurate valuation of CS and it is
about 10degC, what policy implications might that have for the timing
of geoengineering deployments?
Robert Chris
On Feb 20, 9:48 pm, Ken Caldeira <kcalde...@carnegie.stanford.edu
<mailto:kcalde...@carnegie.stanford.edu>>
wrote:
> The attached papers are relevant.
>
> On Mon, Feb 20, 2012 at 11:32 AM, David Mitchell
<david.mitch...@dri.edu <mailto:david.mitch...@dri.edu>>wrote:
>
>
>
>
>
>
>
> > From paleoclimate data with a geologic time-scale, climate
sensitivity may
> > be ~ 2.7 times larger than the Charney value of ~ 3 deg. C (
climate
> > feedback factor 0.75 deg. C/W m2; characteristic of the fast
feedbacks in
> > GCMs) based on a recent paper from Jeff Kiehl:
> > Kiehl, J., 2011: Lessons from Earth's Past. Science, Vol.
331, 14 Jan.,
> > 158-159, DOI: 10.1126/science.1199380.
>
> > David Wasdell has written about climate sensitivity featuring
the work of
> > Kiehl and others (see attached) but I don't know whether that
document ever
> > got published. Wadham's paper discusses some of the arguments
Mike has
> > made.
>
> > These papers do not indicate or suggest that climate
sensitivity may save
> > us from global warming.
>
> > David Mitchell
>
> > On 2/20/2012 8:57 AM, Mike MacCracken wrote:
>
> >> Just to be clear--
>
> >> The radiative forcing due to CO2 increases is
logarithmic--that is, the
> >> radiative forcing going from 300 to 600 ppm is the same as
going from 600
> >> to
> >> 1200 ppm. Thus, the forcing due to the rising CO2
concentration does
> >> decrease on a per ppm basis.
>
> >> However, forcing is not sensitivity, and like Tom Wigley, I
recall papers
> >> that have done a good bit of testing of plausible changes in
concentration
> >> and the sensitivity (that is, the temperature change for a
doubling of the
> >> CO2 concentration) is, near as it can be estimated, pretty
linear. At
> >> lower
> >> temperatures one may have more snow/ice albedo feedback, but
at higher
> >> temperatures one has more water vapor and, very likely,
carbon cycle
> >> feedback (carbon cycle feedback including thawing permafrost
and releasing
> >> CO2/CH4, out-gassing of CO2 from warmer ocean, higher
airborne fraction as
> >> ocean overturning slows, etc.). Given the warmth of the
Cretaceous, it is
> >> hard to be sanguine about adding more and more CO2 to the
atmosphere. And
> >> given the heat of Venus, which absorbs less solar per square
meter than
> >> the
> >> Earth even though closer to the Sun, it seems really
difficult to argue
> >> that
> >> adding greenhouse gases to an atmosphere leads to a plateau
in the
> >> response.
>
> >> Mike MacCracken
>
> >> On 2/20/12 7:38 AM, "Tom Wigley"<wig...@ucar.edu
<mailto:wig...@ucar.edu>> wrote:
>
> >> Sensitivity is the equilibrium change in global-mean
temperature per
> >>> unit of radiative forcing. Linearity has been demonstrated
up to much
> >>> higher forcings than will ever be reached by even the most
pessimistic
> >>> scenarios.
>
> >>> Early IPCC reports might cover this. I recall work by Kiehl
on this back
> >>> in the mid 1980s -- too far back to recall the reference.
>
> >>> Tom.
>
> >>> +++++++++++++++++
>
> >>> On 2/20/2012 5:28 AM, Robert Chris wrote:
>
> >>>> I am engaged in discussion with a modestly prominent
climate skeptic
> >>>> who argues that global warming isn't a problem because as CO2
> >>>> concentrations rise climate sensitivity reduces. I recall
coming
> >>>> across this notion before but I don't know how much
peer-reviewed work
> >>>> has been done on it. I'd appreciate some help with
references to peer-
> >>>> reviewed papers that address the idea that climate
sensitivity may be
> >>>> logarithmic rather than linear so that as atmospheric CO2
> >>>> concentrations rise the effective climate sensitivity
reduces and
> >>>> discuss the likely levels at which this reduction becomes
significant
> >>>> in terms of reducing the GWP of CO2.
>
> >>>> -----------------------------
> >>>> Robert Chris
> >>>> The Open University
> >>>> r.g.ch...@open.ac.uk <mailto:r.g.ch...@open.ac.uk>
>
> > --
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>
>
>
> Reisinger_et_al_ERL2011.pdf
> 570KViewDownload
>
> Caldeira_Kasting_Nature1993.pdf
> 417KViewDownload
>
> Pagani_et_al_Science2006.pdf
> 291KViewDownload
>
> Matthews_et_al_Nature2009.pdf
> 496KViewDownload
>
> Matthews_Caldeira_GRL2008.pdf
> 716KViewDownload
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