cc: "\"WGI-chap6-ar4\"" date: Wed, 6 Sep 2006 17:28:53 +0400 from: "Olga Solomina" subject: Re: [Wg1-ar4-ch06] urgent IPCC need to: "Fortunat Joos" Dear Fortunat, Many thanks for your suggetions (including the glacier bullet). It would be nice to include the point that the early Hol warming was orbitally triggered, but it is hard to find an elegant way to do it in this bullet. We have to be careful because in the Holocene subchapter we say that there were no periods (or we cannot detect them) of global (or hemispheric-scale) warming previousely to 20th century. Cheers, olga ----- Original Message ----- From: "Fortunat Joos" To: "Jonathan Overpeck" ; "WGI-chap6-ar4" Cc: "Martin Manning" Sent: Wednesday, September 06, 2006 2:57 PM Subject: Re: [Wg1-ar4-ch06] urgent IPCC need > Dear Peck, Eystein, Martin and co, > > Went again carefully through the ES and have removed a few typos and > added some clarificaton to avoid ambiguities. All changes indicated in > brownish color. > > KEITH: suggest to add the words Northern Hemisphere in one of the > bullets to really make it unambigous > > Holocene glacier extent: suggest to clarify that Holocene warming was > related to orbital forcing > > last 2 ka bullet: Do we have nothing to say about droughts in Asia. We > mention Africa and Americas, but not Asia/Europe/Australia. So the > bullets may be regarded as not balanced. > > Hope the proposed rewording of the feedback bullet is acceptable to > everybody and reflects adequately what is said in the chapter. > > • 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. > > Not sure David is happy with it? > > Turning to the issue raised by Martin to make a statement on global > temperature of the last millennium. How about adding the following > sentence to the bullet, linking GHG and global temperature? > > • 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. The small preindustrial greenhouse gas variations also provide > indirect evidence for a limited range of decade- to century-scale > variations in global temperature. > > > I still believe that the points we made in the Gerber et al. study are > valid. However, I also like to point out that our findings have not been > scrutinized by others and there is hardly any literature investigating > the relationship between CO2 or CH4 and climate over the past > millennium. There are a number of open issues such as > > - The response of atmospheric CO2 to a change in climate varies greatly > among the C4MIP model (factor four or so). We know some weaknesses of > the model that behave extreme in this respect, however, there is no > basis for excluding them from the assessment at the moment. > - Land use is a factor that has not been properly addressed yet. > - studies addressing the link between CH4 and climate over the last > millenium are missing > > I think more studies on past CO2 and CH4 variations are needed to > corrobate the Gerber et al. results. Perhaps, then the point can be made > more vigourously and convincingly in the AR5. > > With best wishes, Fortunat > > Jonathan Overpeck wrote: >> >> Hi Martin - I can see what you mean, and hope that Fortunat can come up >> with a clever idea to clarify that the modest trace gas variations argue >> for modest global temp change over the last 1000 year, consistent with >> the reconstructions of modest NH temperature change over this interval. >> >> Perhaps... >> >> The small variations in preindustrial CO2 and CH4 concentrations over >> the past millennium are consistent with millennial-length proxy Northern >> Hemisphere temperature reconstructions in supporting only a limited >> likely role of solar climate forcing. >> >> >> Thanks both, cheers, peck >> >> >>> 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: Don’t 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 650’000 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: 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 >> >> >> >> -- >> >> Jonathan T. Overpeck >> Director, Institute for the Study of Planet Earth >> Professor, Department of Geosciences >> Professor, Department of Atmospheric Sciences >> >> Mail and Fedex Address: >> >> Institute for the Study of Planet Earth >> 715 N. Park Ave. 2nd Floor >> University of Arizona >> Tucson, AZ 85721 >> direct tel: +1 520 622-9065 >> fax: +1 520 792-8795 >> http://www.geo.arizona.edu/ >> http://www.ispe.arizona.edu/ > > -- > > 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: http://www.climate.unibe.ch/~joos/ > > -------------------------------------------------------------------------------- > _______________________________________________ > Wg1-ar4-ch06 mailing list > Wg1-ar4-ch06@joss.ucar.edu > http://lists.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06 > _______________________________________________ Wg1-ar4-ch06 mailing list Wg1-ar4-ch06@joss.ucar.edu http://lists.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06