Wednesday, May 2, 2012

3687.txt

cc: WGI-chap6-ar4 <wg1-ar4-ch06atXYZxyzs.ucar.edu>
date: Mon, 04 Sep 2006 15:21:07 -0600
from: Martin Manning <mmanningatXYZxyznoaa.gov>
subject: Re: [Wg1-ar4-ch06] urgent IPCC need
to: Fortunat Joos <joosatXYZxyzmate.unibe.ch>, Fortunat Joos <joosatXYZxyzmate.unibe.ch>

Dear Fortunat and colleagues
Thanks for copying me on your discussion. Can I just try to clarify what I meant by one of
the questions raised on your earlier version of the ES. This refers to the bullet:
* The small variations in preindustrial CO2 and CH4 concentrations over the past millennium
are consistent with millennial-length proxy Northern Hemisphere temperature
reconstructions; climate variations larger than indicated by the reconstructions would
likely yield larger concentration changes. [my question: Dont the small preindustrial
variations in CO2 and CH4 also put a constraint on global temperature changes?] [Peck's
comment: Fortunat should we just delete the words Northern Hemisphere? Martin is right, and
this makes the statement more powerful than just supporting NH proxy records.]

[Fortunat's response: There are hardly reliable global reconstructions to compare with.
Please do not delete NH! The literature on the issue is limited. Thus, I hesitate to make
to bullet too strong.]
I was thinking of Gerber et al (2003) (Climate Dynamics) and on going back and looking at
this again I see that there are some subtle distinctions being made there between past NH
temperatures and past global temperatures. But there still seem to be some implications for
global temperatures. E.g. the abstract says:
"Simulations where the magnitude of solar irradiance changes is increased yield a mismatch
between model results and CO2 data, providing evidence for modest changes in solar
irradiance and global mean temperatures over the past millennium and arguing against a
significant amplification of the response of global or hemispheric annual mean temperature
to solar forcing."
Clearly deleting "Northern Hemisphere" in the first part of the bullet would go too far but
is there a case for a short additional sentence on the end of the bullet in the ES along
that lines of that sentence pulled from Gerber et al?
Regards
Martin
At 09:02 AM 9/4/2006, Fortunat Joos wrote:

Content-Type: text/plain; charset=windows-1252; format=flowed
X-MIME-Autoconverted: from 8bit to quoted-printable by tomcat.al.noaa.gov id
k84F2V7S002068
Uups,
Sorry for sending of the file too early. Would like to correct the suggested bullet on
orbital forcing and feedbacks:
The widely-accepted orbital theory suggests that glacial-interglacial cycles
occurred in response to orbital forcing. The large response of the climate system
implies a strong positive amplification of this forcing. Changes in greenhouse gas
concentrations, ice sheet growth and decay, ocean circulation and sea ice changes,
biophysical feedbacks, and aerosol (dust) loading have very like contributed to this
amplification.
We do not need to refer to the magnitude of the orbital forcing. Although it is small in
global annual mean it is very large seasonally.
With best wishes,
Fortunat
Fortunat Joos wrote:

Hi Peck and all,
Sorry was not in over the weekend.
It seems that my earlier comments and suggestions for the ES got overlooked. All my
changes are detailed in the attached revised ES file. Please refer to this file for my
detailed comments.
The most important proposals are given in ascii below for those that do not want to open
the attached file(s).
I copy this also to Martin Manning for information.
Finally, all authors of the chapter should definitly see the latest version and give
their agreement.
With best wishes, Fortunat
Here first my earlier suggestions also in the file from August 15.
1. bullet
"The sustained rate of increase over the past century in the combined radiative forcing
from the three well-mixed greenhouse gases carbon dioxide (CO2), methane (CH4), and
nitrous oxide (N2O) is very likely unprecedented in at least the past 16,000 years.
Pre-industrial variations of atmospheric greenhouse gas concentrations observed during
the last 10,000 years were small compared to industrial era greenhouse gas increases,
and were likely mostly due to natural processes."
1. bullet in 2000 year section:
"It is very likely that the average rates of increase in CO2 and in the combined
radiative forcing from CO2, CH4 and N2O concentration increases have been at least five
times faster over the period from 1960 to 1999 than over any other 40-year period during
the past two millennia prior to the Industrial Era."
1. bullet in feedback section:
What does the original bullet mean to a non-specialist? Non-linear can be anything
(exponential decay? An oscillation?). Why should the small size of the orbital forcing
suggest non-linearity? What about GHGs? Bullet seems very verbose. What does the last
sentence mean? Is this not a contradiction to the figure showing the LGM forcing? In
this figure, a consensus view is given on the magnitude of past forcing. Dust loading
and vegetation albedo feedback/forcing are generally considered to be much smaller than
ice sheet feedbacks/forcing.
What should be said is something like:
"The widely-accepted orbital theory suggests that glacial-interglacial cycles occurred
in response to globally small changes in orbital forcing. The large response of the
climate system to a globally small forcing implies a strong positive amplification of
this forcing. Changes in greenhouse gas concentrations, ice sheet growth and decay,
ocean circulation and sea ice changes, biophysical feedbacks, and aerosol (dust) loading
have very like contributed to this amplification."
The points are
refer to the orbital theory to caveat the statement as Milankovitch theory is not yet
proven.
- strong amplifications occurred.
- list the factors that contributed to the amplification.
Now to the more recent discussion. Suggestions are again in the attached file in green.
- I agree with Peck that we should say something about 1998 issue.
- I think merging the first and last section would overcome some of the weaknesses of
the previous draft in particular with respect to amplification and orbital theory:
What is the relationship between past greenhouse gas concentrations and climate and the
role of biogeochemical and biophysical feedbacks?
The sustained rate of increase over the past century in the combined radiative
forcing from the three well-mixed greenhouse gases carbon dioxide (CO2), methane (CH4),
and nitrous oxide (N2O) is very likely unprecedented in at least the past 16,000 years.
Pre-industrial variations of atmospheric greenhouse gas concentrations observed during
the last 10,000 years were small compared to industrial era greenhouse gas increases,
and were likely mostly due to natural processes.
It is very likely that the current atmospheric concentrations of CO2 (380 ppm) and
CH4 (1760 ppb) exceed by far the natural range of the last 650000 years. Ice core data
indicate that CO2 varied within of 180 to 300 ppm and CH4 within 320 to 790 ppb over
this period. Over the same period, Antarctic temperature and CO2 concentrations co-vary,
indicating a close relationship between climate and the carbon cycle.
The widely-accepted orbital theory suggests that glacial-interglacial cycles
occurred in response to globally small changes in orbital forcing. The large response of
the climate system to a globally small forcing implies a strong positive amplification
of this forcing. Changes in CO2 and other greenhouse gases, ice sheet growth and decay,
ocean circulation and sea ice changes, biophysical feedbacks, and aerosol (dust) loading
have very like contributed to this amplification.
It is unlikely that CO2 variations have triggered the end of glacial periods.
Antarctic temperature started to rise several centuries before atmospheric CO2 during
past glacial terminations.
It is very likely that marine carbon cycle processes were primarily responsible for
the glacial-interglacial CO2 variations. The quantification of individual marine
processes remains a difficult problem.
It is virtually certain that millennial-scale changes in atmospheric CO2 associated
with individual Antarctic warm events were less than 25 ppm during the last glacial
period. This suggests that the associated changes in North Atlantic Deep Water formation
and in the large-scale deposition of wind-borne iron in the Southern Ocean had limited
impact.
Paleoenvironmental data indicate that regional vegetation composition and structure
are very likely sensitive to climate change, and can, in some cases, respond to climate
change within decades.
It is likely that earlier periods with higher than present atmospheric CO2
concentrations were warmer than present. This is the case both for climate states over
millions of years (e.g., in the Pliocene, ca. 5 to 3 million years ago) and for warm
events lasting a few hundred thousand years (i.e., the Paleocene-Eocene Thermal Maximum,
55 million years ago). In each of these two cases, warming was likely strongly amplified
at high northern latitudes relative to lower latitudes.

--
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Phone: ++41(0)31 631 44 61 Fax: ++41(0)31 631 87 42
Internet: [1]http://www.climate.unibe.ch/~joos/

--
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** Please note that problems may occur with my @noaa.gov address
Dr Martin R Manning, Director, IPCC WG I Support Unit
NOAA Aeronomy Laboratory Phone: +1 303 497 4479
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