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Second phase of paleoclimate modelling intercomparison
project
M. Crucifix, P. Braconnot, S. Harrison, B. Otto-Bliesner
To cite this version:
M. Crucifix, P. Braconnot, S. Harrison, B. Otto-Bliesner. Second phase of paleoclimate modelling
in-tercomparison project. Eos, Transactions American Geophysical Union, American Geophysical Union
(AGU), 2005, 86 (28), pp.264. �10.1029/2005EO280003�. �hal-03244189�
Eos, Vol. 86, No. 2 8 , 1 2 July 2005
bulletins, and makes available to the interest ed researchers software tools for seismogram digitization. Important steps for successful preservation of the heritage include Internet a c c e s s to the data, high-resolution scanning, and large storage facilities c o m b i n e d with the organizational structure providing record and bulletin retrieval, identification, and s c a n n i n g . Easy a c c e s s to c o l l e c t i o n s of these s e i s m i c records c o u l d prompt m o d e r n reap praisals of historical earthquakes and lead to reevaluations of s e i s m i c hazard.
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By devoting an entire chapter of the fourth assessment report (AR4) to paleoclimates, the Intergovernmental Panel on Climate Change (IPCC) has recognized that studying past climates is essential for comprehending the climate system, and h e n c e for predicting its future evolution.
In particular, numerical simulations of past climates, different from today, constitute an independent test of the performance and reliability of the general circulation models c o m m o n l y used for climate predictions.This idea is the motivation for the Paleoclimate Modelling Intercomparison Project ( P M I P ) , a long-standing initiative endorsed by the World Climate Research Programme and the Interna tional Geosphere and Biosphere Programme. The focus has s o far b e e n on two reference periods, c h o s e n as being the most representa tive of c o l d and warm climate intervals in the recent past: the Last Glacial Maximum (LGM, 21,000 years ago) and the mid-Holocene ( 6 0 0 0 years a g o ) .
The first phase of PMII? launched in 1992, was based on analysis of atmospheric general cir culation models. PMIP 1 met with considerable success, with 67 model experiments archived in a central database and over 70 papers published in the refereed literature. One of the greatest achievements of PMIP 1 was to provide a framework for paleoclimate modeling by bringing a community of climate modelers and field experts together. In 2002, the PMIP steering committee decided, therefore, that the time had c o m e to define new numerical experiments that take advantage of the new generation of atmosphere-ocean-vegetation coupled models
[Harrison et al, 2002] .With these new simula
tions PMIP 2 also hopes to extract quantitative information on climate sensitivity in order to better predict the c o n s e q u e n c e s of climate change on human societies.
The first PMIP 2 workshop, held in April 2005, gathered most of the scientists involved in the project.The attendance spanned the different representative disciplines (climate modeling,
Acknowledgments
The activity described in this article would not have been possible without the contribution of the SISMOS Team (http://sismos.ingvit/index2. php?bframe=organization.php) which is here acknowledged.Thanks also to Graziano Ferrari of SGA Storia Geologia Ambiente, a promoter of the EuroSeismos project, and to Anthony Lomax for revising and editing this manuscript. Parts of the SISMOS database have been designed by Finsiel,an Italian software company
geophysics, biology, palynology geochemistry and paleoceanography) with 65 scientists from five continents.
On the agenda were a discussion of model results obtained so far (including a compari son with p a l e o d a t a ) , a n overview of newly available paleoclimate data syntheses, and plans to widen the s c o p e of PMIP 2 by defin ing experimental protocols for other periods in the past.
A Series of New Paleoclimate Simulations
Compared with PMIP l , t h e PMIP 2 project considers, for e a c h period, a suite of numeri cal experiments that differ by the n u m b e r of c o m p o n e n t s of the Earth system that are inter actively taken into account: AGCM simulations use atmosphere general circulation models with prescribed s e a surface temperatures; OAGCMs have a c o m p o n e n t calculating the dynamics of the o c e a n ; and OAVGCMs are coupled to a dynamic vegetation model.
The high scientific potential of this ap proach was highlighted in a series of presenta tions describing recent OAGCM and OAVGCM simulations. Y Zhao showed how the shoaling of the mixed layer in the Indian O c e a n en h a n c e s the response of the Indian m o n s o o n to the c h a n g e s in orbital forcing.This is a good e x a m p l e of positive feedback of the o c e a n re sponse on the atmosphere dynamics. Having interactive vegetation may further e n h a n c e the response of the atmosphere with, in turn, c o n s e q u e n c e s to the structure of the o c e a n mixed layer. Such an ocean-vegetation synergy needs to b e taken into a c c o u n t to understand the abundant m o n s o o n rainfall in the Sahel during the mid-Holocene [Braconnot et al, 2004].
Another goal of PMIP 2 is to maintain a database of model results in which long-term m e a n s and individual years are archived. Information on interannual and interdecadal variability c a n therefore b e extracted. Specifi cally, preliminary comparisons of the El N i h o -Southern Oscillation and North Atlantic Os cillation signals in PMIP 2 experiments were shown by U.Merkel and R.Gladstone.The first
References
Kanamori, H. (1988), Importance of historical seis mograms for geophysical research, in Historical
Seismograms and Earthquakes of the World, edited
by W H. K. Lee et al.,pp. 16-63, Elsevier, New York. Pintore,S.,M.Quintiliani,and D.Franceschi (2005),
Teseo: A vectoriser of historical seismograms,
Comput. GeoscL, 3/,doi:10.1016/j.cageo.2005.
04.001, in press.
Author Information
Alberto Michelini, Bruno De Simoni,Alessandro Amato,and Enzo Boschi, Istituto Nazionale di Geofisica eVulcanologia.Rome
PMIP 2 model outputs also provided the op portunity to illustrate s o m e innovative analysis techniques (quantification of cloud feedback based on regime analysis, simulations of po tential vegetation,lake-level modeling).
Apart from using more sophisticated climate models, PMIP 2 uses up-to-date information to define the experiments, including the latest reconstruction of the Last Glacial Maximum topography (ICE-5G) and a river routing s c h e m e derived from geological evidence c o m p l e m e n t e d by hydrological modeling. It is therefore essential to determine to what ex tent these refinements improve the ability of state-of-the-art climate models to reproduce past climatic data.
This question was discussed at the work shop. On the o n e hand, a series of posters was devoted to specific sensitivity experiments analyzing the role of river routing, horizontal resolution, and freshwater fluxes on simula tion results. On the other hand, a s c h e m e was developed during the meeting (S. Har rison) that objectively determines the level of agreement between models and data on the basis of a series of qualitative but robustly d o c u m e n t e d paleoclimatic features, for ex ample, abundant m o n s o o n rainfall in the Sahel throughout the mid-Holocene. It was also shown (A. Abe-Ouchi) how quantitative information produced from paleoclimate records, such as the amplitude of the tropical Pacific cooling at the Last Glacial Maximum, may b e used to infer constraints on climate sensitivity on the basis of a large e n s e m b l e of climate simula-tions.This technique could provide a valuable contribution to the IPCC.
Promising Advances in Data Reconstructions
The meeting was equally rich on the data side. Pollen data and macrofossils (M. Kerwin, M. Edwards) show that the warm est e p o c h between the Last Glacial Maximum and today (the H o l o c e n e thermal optimum) occurred as early as 10,000 years ago in the Alaska-eastern Siberia s e c t o r (Beringia), while northeastern America s u m m e r tempera tures hit their maximum less than 6000 years ago.The late thermal optimum in northeastern Canada is partly linked to the p r e s e n c e of remainders of the Laurentide I c e Sheet until about 7000 years ago. Perhaps in c o n n e c t i o n with the disappearance of the Laurentide Ice Sheet, cysts of dynoflagellates reveal a sharp increase in surface salinity and mixed-layer depth around 7500 years ago in the Labrador S e a (A. de Vernal).
M E E T I N G S
Second Phase of Paleoclimate Modelling
Intercomparison Project
W h e n possible, a multi-proxy approach is preferable for inferring robust information on past climate evolution. A good e x a m p l e was given for southeastern Brazil (B.Turcq), where lake-level reconstructions,speleothemes (e.g., stalagmites),and pollen fossils allow the docu mentation of a continuous increase in precipi tation s i n c e the Last Glacial Maximum.
Progress has also b e e n m a d e about the knowledge of past i c e sheets. Geophysical constraints on the history of the Laurentide Ice Sheet ( W R. Peltier) allow the inferring of the e x i s t e n c e of large freshwater meltwater runoff flow into the Arctic during the Younger Dryas ( 1 2 , 7 0 0 - 1 1 , 7 0 0 years ago).There are also an increasing n u m b e r of attempts to extract indices of past climate variability from high-resolution paleoclimatic records, al though it has not b e e n possible so far to infer information on interannual variability that is spatially consistent (S. Brewer). Finally, detailed analysis of modern climate and pollen data re mains essential, as illustrated by an extensive survey of modern bioclimatic relationships presented by B.Thompson.
Widening the Scope: New Targets for PMIP Experiments
Although the mid-Holocene and LGM continue to b e of interest, other periods pose interesting challenges. Specifically, PMIP 2 has e x p a n d e d the set of standard experiments to include simulations of the previous inter-glacial/glacial transition (this is the "glacial inception," 115,000 years a g o ) , the early Ho-l o c e n e (9000 years ago), the Younger Dryas (the c o l d period observed in different regions of the Northern Hemisphere between 12,700 and 11,700 years a g o ) , a n d the abrupt cooling event 8 2 0 0 years ago.
The focus on glacial inception is motivated by s o m e earlier experiments suggesting that
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Almost a l o n e in the world of s c i e n c e , there is a substantial U.S. effort to discredit s o m e basic conclusions in the global warming debate. There are always legitimate reasons to query scientific conclusions, but the tenor of the d e b a t e has taken on a flavor of its own. S i n c e the epicenter of the dispute is in Washington, D.C.,the suspicion arises that not all of the discussion is business-as-usual scientific dis agreement.
The most recent example of the heightening level of the dispute involves a 23 J u n e 2005 letter from U.S.Rep. J o e Barton (R-Tex.), chair of the House Committee on Energy and Com merce, to Michael Mann (University of Vir ginia) and his collaborators, Raymond Bradley
Eos, Vol. 86, No. 28,12 July 2005
(University of Massachusetts) and Malcolm Hughes (University of Arizona). T h e dispute centers on the much discussed "hockey stick" reconstruction of Mann et al. [ 1 9 9 8 , 1 9 9 9 ] . In those reconstructions, the twentieth century warming stands well above Northern Hemi sphere temperature fluctuations of the last 1000 years. Other investigators, using s o m e of the s a m e data but with different approaches, have also reconstructed temperatures of the last millennium ( s e e Mann et al. [2003] for a summary discussion). In general, there is more agreement than disagreement among the various reconstructions.The differences stem mainly from the scaling of the oscillations, but in all c a s e s the late twentieth century is a n o m a l o u s in a millennial context.
The discussions on the hockey stick would
fique (CNRS,France),Commissariat a l'Energie Atomique (CEA,France),the international pro grams on climate variability and predictability (CLIVAR) and Past Global Changes (PAGES). The local organization and the program were settled by PBraconnot and B.Otto-Bliesner with the help of the PMIP 2 steering committee and the Laboratoire des Sciences de Climat et de l'Environnement (CEA-CNES, France) climate modeling group. S.Galot cared for the admin istration and French language support.Travel funding for many of the U.S. participants was pro vided by the U.S. National S c i e n c e Foundation's Earth System History program and U.S. National Oceanic and Atmospheric Administration's Office of Global Programs.
References
Braconnot, P, S. P Harrison, S. Joussaume, C. D. Hewitt, A. Kitoh, J. E. Kutzbach, Z. Liu, B. Otto-Bliesner, J.Syktus,and N.Weber (2004),Evaluation of PMIP coupled ocean-atmosphere simulations of the mid-Holocene, in Past Climate Variability Through
Europe and Africa, edited by R.WBatterbee et al.,
pp. 515-533, Springer, New York.
Harrison, S. P, PBraconnot, S. Joussaume, C. D. Hewitt, and R.J.Stouffer (2002), Comparison of paleocli mate simulations enhances confidence in models,
Eos Trans.AGU, &3(40),447.
—M. CRUCIFIX, Hadley Centre, Met Office, Exeter, Devon,U.K.; P BRACONNOT, Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS,Gif-sur-Yvette, France; S. P HARRISON, School of Geographical Sciences,University of Bristol, U.K.; and B. OTTO-BLIESNER, Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colo.
For additional information, contact M. Crucifix; E-mail: [email protected].
require many pages to describe in detail, but an apparent trigger for the 23 J u n e development goes b a c k to a request about three years ago by a Canadian investigator, Steven McIntyre,for all the files, data sets, algorithms, and source c o d e s that went into the Mann et al. reconstruction. Mclntyre is a semi-retired mineral trader with an interest in mathematics, and he wanted to test s o m e of the results of the Mann et al. stud ies. Although the data were already available on a public FTP (file transfer protocol) computer site, Mann provided them in a different format, as requested by Mclntyre.The algorithm was described in the original 1998 Nature paper, but an expanded version was added in 2004 on a Nature supplementary Web site.The source c o d e was not provided b e c a u s e it is consid ered an intellectual property right.
Mclntyre continues to press for more in formation. Not all of this information was provided, in part b e c a u s e of the s h e e r level of work required. B e c a u s e I had also produced a millennial climate reconstruction [Crowley
and Lowery, 2 0 0 0 ] , I too was a recipient of a
request from Mclntyre. I c a n attest that his ini tial message was of a somewhat peremptory
F O R U M
Raising the Ante on the Climate Debate
vegetation and o c e a n feedbacks are essential for explaining year-to-year accumulation of snow in northeastern America at the end of the previous interglacial period.With the PMIP community focusing on fully c o u p l e d OAVGCMs, it is appropriate to revisit this issue. Younger Dryas and 8.2 kyr experiments are an opportunity to obtain information on the stability of the o c e a n circulation, and the con s e q u e n c e s of possible c h a n g e s in its structure, by comparing model outputs with paleocli matic data.The meeting has allowed the defin ing of the corresponding experimental setups.
Several contributions also highlighted the necessity of using Earth system models of intermediate complexity to develop analysis methods, explore the parameter s p a c e , and analyze the response of climate over long tim-escales. For example, it was shown that several thousands of years are n e e d e d by the climate system to recover from a perturbation of the North Atlantic freshwater b a l a n c e . Furthermore, the characteristic response time differs for gla cial and interglacial conditions (I.Ross, E . B a u e r ) .
A. Koutavas (LDEO, C o l u m b i a ) and A. Ga-nopolski (Potsdam Institute for Climate Impact Research, Germany) were awarded the best poster prizes.The meeting also provided the opportunity to tighten social links; and an excursion to the nearby Porquerolles Island nicely c o m p l e m e n t e d the program. Full de tails about the meeting, the project, and how to b e involved in result analysis are available at http://www-lsce.cea.fr/pmip2.
The Paleoclimate Modelling Intercomparison Project Workshop was held on 3 - 8 April 2005, in Giens (Var, France),
Acknowledgments
Financial support to the meeting was provided by Centre National de la Recherche
