date: Wed, 22 Nov 2000 11:12:51 +0100
from: raynaud dominique <raynaud@glaciog.ujf-grenoble.fr>
subject: HIHOL Meeting
to: daniel@erdw.ethz.ch, barnola@glaciog.ujf-grenoble.fr, beer@eawag.ch, berger@astr.ucl.ac.be, dblack@geol.scedu, gcb@ldeo.columbia.edu, pasb@lsce.saclay.cea.fr, rbradley@geo.umass.edu, k.briffa@uea.ac.uk, drdendro@ldeo.columbia.edu, crucifix@astr.ucl.ac.be, ddj@gfy.ku.dk, delmas@glaciog.ujf-grenoble.fr, peter@ldeo.columbia.edu, flueckiger@climate.unibe.ch, scf@unlserve.unl.edu, fujii@pmg.nipr.ac.jp, luis-gonzales@uiowa.edu, uligraf@lsce.cnrs-gif.fr, sandy.harrison@bgc-jena.mpg.de, b.p.horton@durham.ac.uk, eystein.jansen@geol.uib.no, lkeigwin@whoi.edu, andre.lotter@ips.unibe.ch, macdonal@geog.ucla.edu, atle.nesje@geol.uib.no, tas.van.omnen@utas.edu.au, t.osborn@uea.ac.uk, colin.prentice@bgc-jena.mpg.de, r.ramesh@prl.ernet.in, raynaud@glaciog.ujf-grenoble.fr, p.rowe@uea.ac.uk, goseltze@mailbox.syr.edu, sicre@lsce.cnrs-gif.fr, ian.snowball@geol.lu.se, esteig@sas.upenn.edu, sSandy.Tudhope@ed.ac.uk, dirk.verschuren@rug.ac.be, vimeux@lsce.saclay.cea.fr, harvey.weiss@yale.edu, gzielinski@maine.edu

   Dear colleagues and friends,

   Please find enclosed an outline-draft of the conclusions of the HIHOL meeting.
   As you can see below the text needs to be largely completed by most of the HIHOL
   participants. We are also waiting for your comments. Please send your inputs before
   December 4 at Dominique (raynaud@glaciog.ujf-grenoble.fr) and Keith (k.briffa@uea.ac.uk).
   It would be better to enclosed a few  figures (4 to 5) to illustrate our main conclusions.
   After completion we will use this draft for the PAGES Newsletter, the SCAR bulletin and
   possibly EOS.
   We really enjoyed a lot to work with all of you in this HIHOL venture and would like to
   thank you for your contributions (including those you will provide for this document and
   the HOLOCENE issue).
   All the best
   Dominique and Keith

                                        HIHOL CONCLUSIONS

   Should we include a few up-to-the-moment references references?
   Today, the paleo-community maintains its fascination with the large magnitude changes that
   have occurred in the Earths climate system as it shifts periodically from glacial to
   interglacial modes. This research has led to a wealth of information concerning the roles
   and associated changes in insolation, atmospheric composition, oceanic circulation, and ice
   cover, and more recently to the discovery  of rapid and dramatic climatic changes during
   the last glacial period and the last deglaciation.
   Somewhat in contrast, interest in the Holocene, the present warm period following the last
   deglaciation, is gaining added momentum. There are at least two main reasons for this:
          the increasing numbers of high resolution environmental records (of both climate
   and potential climae forcings) from continental, ice core and oceanic sources; and
          the fact that the Holocene is recognised as a period of significance interest for
   understanding the natural variability of climatic and wider environmental systems that
   provide background context  for the study of anthropogenic changes.
   Although the polar record show the Holocene as a period of minor changes (relative to the
   glacial periods) from the viewpoint of low latitudes, the Holocene has been a time of large
   changes especially in hydrological conditions in the inter-tropical zone. Such changes are
   critically important to society today, given the high population in these regions.
   During the 24-26 October 2000, 42 scientists from 13 countries gathered to attend the
   meeting of HIHOL (High Resolution Variability in the Holocene) held in LIsle sur la Sorgue,
   near Avignon,  France, with the support of PAGES, SCAR and NSF.
   The meeting was structured to include presentations and discussions on a number of general
   themes, mainly focussing on different geographic regions associated with specific climate
   vsub-systems:

          climate forcing and global signals(insolation, solar variability, greenhouse gases,
   volcanoes, thermohaline circulation, sea level changes)
          low latitudes (tropical warm pool, Hadley cell, ENSO, monsoons)
          middle latitudes (westerly zones, NAO)
          high latitude, polar regions
          modeling efforts.
   The last afternoon was devoted to a general discussion and the organization of a special
   HIHOL issue of the journal HOLOCENE, in which the latest information on the general themes
   will be summarized in 7 review articles, each addressing one or more of the following
   specific questions:
          What is the best resolved picture of Holocene climate variability that can be
   synthesized in the different regions on millennium, century and annual-to-decadal
   timescales?
          What were the significant changes at these various timescales? Were they in-phase
   or out-of-phase in the different regions and why?
          Were there major synchronous abrupt events and what were their magnitudes  e.g., at
   about  8.2K calendar years ago; at 4K years ago; at 2K years ago; at 540 A.D.?
          Was there a Holocene Climate Optimum, that we prefer to call here Thermal Maximum?
          What is the role of changing seasonal insolation and irradiance on climate changes,
   e.g., low latitude effects on monsoon variability?
          How the carbon cycle changed and why?
    The following is a brief summary of some of the main conclusions of the meeting concerning
   potential climate forcings, the ice core, terrestrial and oceanic records, and recent
   results of climate modeling of Holocene variability.
   Climatic forcings
          Insolation
   Changes of orbital parameters are precisely calculated. Short description of the main
   charateristics during the Holocene (including 6 kyr); comparison with stage 5 and 11. Andre
   Berger.
          Solar activity
   The solar activity affects the solar irradiance and thus contribute to the radiative
   balance of the Earth-Atmosphere system. Direct observations show changes of the solar
   irradiance of 0.15% over a solar cycle (about 11 years?). Monitoring of solar type stars
   indicates that fluctuations of up to 1%are potentially possible on longer time scales. The
   changes take mainly place in the uv and infrared wave lengths of the solar spectrum. Long
   term reconstructions of solar activity are based on proxies such as sunspots (and what else
   Jrg?), but are limited to the past centuries. Jrg, could you please summarize the main
   features (Maunder minimum,..). Longer records can be derived from measurements in
   cosmogenic nuclides in ice cores (10Be, 36Cl) and tree rings (14C). Jrg, what are the main
   trends of these records during the Holocene?
   Can we interprete the Holocene records of solar activity in terms of radiative forcing
   changes (in W m-2) (Jrg)?
          Greenhouse gases
   The ice core record of greenhouse trace gases is now documented for CO[2], CH[4] and N[2]O.
   These species experienced small long term Holocene changes prior the industrial revolution.
   CO[2] concentrations varied by about 25 ppmv ,with a minimum of about 260 ppmv around 8.2
   kyr BP and the highest concentrations during the last 2000 years. The CH[4] variability is
   of the order of 150 ppbv with the lowest concentrations close to 5,000 BP and the highest
   during the early and late Holocene. The N[2]O concentrations vary between xxx and yyy ppbv
   (thank you Jacqueline for completing) and seem to parallel the CO[2] trend. Provide here
   the corresponding forcings in w/m^2.
          Volcanoes
   Most of the information arises from the ice record (true Greg?).Explosive sulfur-rich
   volcanic eruptions not only force annual climate, but they can also play a significant role
   in decadal-scale forcing throughout the Holocene. These eruptions seem to be especially
   effective in enhancing and possibly lengthening cold periods, as seems to occur during the
   Little Ice Age. However the climatic impact of the abundant volcanism recorded in the
   earliest Holocene appears to be overhelmed by high insolation level at this time. Periods
   when volcanism decreases often are characterized by warmer temperatures as this cooling
   component of the climate system is removed.
   The ice record
          Ice cores provide information not only about climate forcings (see above), but also
   on the climatic variability itself. Several records from Antarctica, Greenland, different
   smaller arctic ice caps, and low latitude glaciers in China and South America document the
   changes of the climate through the Holocene at different latitudes. Furthermore the
   borehole temperature profiles keep a memory of the temperature changes occurring at the
   surface. During the HIHOL meeting we essentially discussed the Greenland and Antarctic
   records. The main source of information concerning the Holocene temperature changes over
   Greenland arises from the temperature profile measured in the deep boreholes, GRIP and
   GISP2, drilled in the most central part of the ice sheet (Dorthe, is it only GRIP?).  A
   clear thermal maximum appears during the 8-5 kyr time interval and we also recognise well
   the medieval climatic anomaly (corresponding to a warming in Greenland around xxxx BP) and
   the little ice age in the xx-yy BP time interval. Thank you Dorthe for completing the
   dates. In Antarctica, most of the evidence arise from the isotopic profiles measured along
   the ice cores (Francoise and Tas, can you provide a list). The different profiles all show
   an early thermal maximum around 7 to 9 kyr BP but no other evidence for coherent climatic
   changes including around the medieval and little ice age time intervals.
          The study of the changes in the mass balance of the glaciers under different
   latitudes (but mainly at middle latitudes) also provides useful insights in the climate
   variability through the Holocene. A striking feature is the record of retreats of the
   glaciers in Scandinavia, the Alps and in South America than today during long periods of
   the Holocene. Furthermore the mass balance history of certain glaciers (in Scandinavia and
   the Alps) can provide a record of the North Atlantic Oscillation. Attle, please check this
   part. How long can be the NAO record from the glaciers?
          The ice record finally provides a unique information about global changes having
   occurred in the biosphere and in the oceans. The main observed pre-industrial Holocene
   change in CO[2] concentrations (25 ppmv increase from 7 to 1 kyr BP) is interpreted as a
   cumulative continental release of about 195 GtC in connection with a change from warmer and
   wetter mid-Holocene climate to colder and drier conditions. The CH[4] record confirms, as
   revealed by the terrestrial record, that the latitudinal distribution of continental
   ecosystems and the hydrological cycle experienced very significant Holocene changes.
   Jacqueline, should we say something here about N2O, or wait until the work is submitted?
   The oceanic record
   Thank you to our HIHOLoceaners to provide here the main conclusions (in the spirit of
   this document). In my mind and according to my notes important conclusions are about the
   evidence of abrupt changes (Bond events,, synchronous or not? duration?; the marine event
   at 8.2kyr last longer than the companion recorded in ice ) and the fact that we have no
   robust evidences for changes in thermohaline circulation (except maybe around 10.3 kyr?).
   Is this absence of evidences due to a lack of available appropriate proxies?
   The terrestrial record
   Thank you to our HIHOL terrestrial friends to provide here the main conclusions keeping the
   style of the present document. According to my notes we should highlight the existence of
   large hydrological changes (green Sahara,.). Although heterogeneous, they are coherent at
   certain times (5.2, 4.2 kyrBP,). What should we write about 8.2 BP? How to summarize the
   temporal and spatial distribution of the thermal maxima? The Little Ice Age appears as a
   major Holocene event and could be an appropriate case study? We have indications of
   increasing variability (temperature? hydrological cycle?) during the late Holocene.
   Thermal maxima
   Please contribute here with your conclusive view about thermal maxima during the Holocene.
   Is it fair to say that  the thermal maximum occurred during early Holocene(9-7 kyr BP?) at
   high latitudes than at low latitudes (6kyr BP)?
   Modelling the Holocene climate
   Waiting the contribution of Michel Crucifix. Should include time slice and transient
   experiences. Modeling includes now vegetation and oceanic feedbacks.
   The main holes, which have not been enough discussed during the meeting or which are not
   documented
   Ice core records from the arctic ice caps and tropical glaciers.
   Chemistry and pollen ice-core records.
   Global sea level record: general trends, uncertainties
   The Southern Hemisphere
   Attachment Converted: "c:\eudora\attach\HIHOL conclusions1.doc"
