cc: WGI-chap6-ar4 date: Mon, 04 Sep 2006 15:21:07 -0600 from: Martin Manning subject: Re: [Wg1-ar4-ch06] urgent IPCC need to: Fortunat Joos , Fortunat Joos 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. -- Climate and Environmental Physics, Physics Institute, University of Bern Sidlerstr. 5, CH-3012 Bern Phone: ++41(0)31 631 44 61 Fax: ++41(0)31 631 87 42 Internet: [1]http://www.climate.unibe.ch/~joos/ -- Recommended Email address: mmanning@al.noaa.gov ** 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 325 Broadway, DSRC R/CSD8 Fax: +1 303 497 5628 Boulder, CO 80305, USA _______________________________________________ Wg1-ar4-ch06 mailing list Wg1-ar4-ch06@joss.ucar.edu http://lists.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06