date: Wed, 22 Nov 2000 11:12:51 +0100 from: raynaud dominique 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 Jûrg?), but are limited to the past centuries. Jürg, 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). Jürg, 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) (Jürg)? · 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 HIHOL»oceaners» 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"