date: Fri, 11 Dec 1998 11:22:06 +0000 from: John Shepherd subject: Multi-millennial ESM to: gjjenkins@meto.gov.uk, k.briffa@uea.ac.uk Message also sent to : modellers, sci div heads, centre/survey directors, a.watson, bill, j.gould, m.fasham, p.liss, p.williamson, r.dickson, t.tyrrell, tom anderson, j.gash Dear Colleague Herewith as body text and as a Word 6 attachment an updated version of an outline proposal (which some of you have seen before) for a project which I am planning to develop. I think it's pretty much self-explanatory. I hope to convene a workshop to kick the idea around early in the New Year, with a view to submitting a full proposal in summer 1999... All expressions of interest, comments and suggestions are invited. With best wishes John ---------------------------------------------------------------------------- ---------------------------------------------------------------- Third Draft Straw-man Proposal for a NERC Cross-Board Initiative Consortium Project Multimillennial Models of the Earth Climate System A) Aims 1) To build an integrated model of the Earth's climate system, including the ocean, atmosphere, cryosphere and biosphere, capable of integration for about one million years. 2) To test its ability to reproduce natural variations of Earth climate through several major glacial/interglacial cycles. 3) To improve the model to the point where it has significant predictive utility in assessing the combined effects of natural and man-made climate forcing. B) Background and Rationale We cannot be confident of any long-term predictions of climate change because we do not yet understand Earth's climate system : in particular the glacial/interglacial cycles which sometime occur. These are believed to be due to an enhanced response (positive feedback) of the atmosphere/ocean/cryosphere/biosphere coupled system to weak solar forcing (Milankovitch cycles), but a full explanation is lacking. It is difficult to evaluate proposed mechanisms quantitatively, because integrated dynamic models of the complete system are not generally available. The most fully developed model is possibly that of the Potsdam Institute for Climate Research, which is planned to embrace social and economic factors too (which may be extremely difficult to do well). [note: the status of other integrated models needs to be checked] It is suggested that the scientific community in the UK is uniquely well placed to create an integrated model of the Earth Climate system, drawing on expertise from NERC Centres & Surveys, the Hadley Centre, and other supported groups. Since we do not believe that we yet understand the system, the model would be exploratory rather than predictive, at the outset, and involve a high risk of failing to simulate the natural system for some time. Nevertheless, use of such models is a necessary part of developing our understanding and evaluating the credibility and magnitude of proposed mechanisms, and the failures should be instructive. Testing and validation will require comparison with palaeodata on temperature, ocean circulation, productivity, etc. This may probably best be done by attempting to simulate the occurrence (or not) of ice-ages as a function of solar forcing, and continental and oceanic configurations, for which data exist in the geological record. C) Method & Model Structure The model will need to incorporate suitable representations of the oceans, the atmosphere, the cryosphere (ice-caps and sea-ice), the biosphere (marine and terrestrial) and certain aspects of the lithosphere (variable continental configurations, erosion and calcium run-off, at least). At present GCM-based integrated climate models such as those of the Hadley Centre are just capable of integration for about one millennium. To permit multiple realisations of integrations one thousand times longer will require extremely simplified representations of most components of the system, with very carefully selected parameterisations of many important processes (e.g. clouds, deep water formation, and atmospheric transport). The longest times scales involved are those for ice-sheet dynamics and ocean chemistry (the calcium/carbonate system), and these will need to be represented with most detail and realism. Other aspects may be modelled using highly simplified (and possibly transient equilibrium) representations. Modest geographical resolution will be required to enable latitudinal gradients (important for ice dynamics) and continental configurations, which are important in determining oceanic heat transport, to be represented. The model parameterisations should be derived from theoretical considerations, and calibrated using comparison with field data and/or the results of more detailed models of subsystems, run for shorter time periods, such as those of the Hadley Centre and those to be developed under the Prescient Programme. The model should almost certainly be modular, to enable alternative representations of subsystems to be incorporated, evaluated and compared easily. Careful attention to the definition and implementation of interface schemes will therefore be required. Such a structure will also permit and facilitate involvement of a broad (and probably distributed) community in the project. However, since the goal is the creation of an integrated tool, the project needs to be a rather highly integrated and managed effort - a consortium project rather than a conventional thematic programme. It would therefore be similar to the early phase of the UGAMP programme (now designated as core-strategic). A tentative outline of a possible structure and scope of the model for each major subsystem is given below. The initial spatial resolution might be of the order of 10 deg latitude by 30 deg longitude, with (say) 5 levels in both the atmosphere and the ocean. Atmosphere A global spatially resolved radiative/convective or energy balance model (?), including parameterised representations of meridional heat (and water) transport, the effects of water vapour and green-house gases on transmission, emissivity and radiation balance, and exchanges with the land, oceans, and cryosphere, including precipitation and evaporation. Ocean Multiple meridional-vertical representations (two or three per ocean, linked via the Southern Ocean (i.e. similar to that of Stocker (1997)). CO2/carbonate/calcium chemistry, including calcite formation/dissolution, needs to be incorporated, as do biological production, organic & inorganic carbon burial, and interchanges with the atmosphere and cryosphere. Parameterisation of deep-water formation (and therefore the meridional circulation) will be a crucial feature (to be derived from process models?). Cryosphere A model of the thickness and latitudinal extent of sea-ice and ice-sheets, and their dynamics, accounting for the presence/absence of land, will be needed. This module will be closest to the state-of-the-art representations in this field. Effects on sea-level and ocean temperature and salinity must be included because of possible transient (?) effects on ocean circulation. Biosphere (a) Terrestrial : to be determined : a simple (transient-equilibrium?) representation of biomass and its growth/decay for latitudinal zones on each continent (or a coarse subdivision thereof) may be adequate. Effects on albedo and interaction with the hydrosphere should be included (as simple parameterisations) (b) Marine A simple (NPZD?) representation of marine production needs to be incorporated and linked to the carbonate chemistry, to represent the carbon cycle and the interactions with atmospheric CO2, so that both natural and anthropogenic effects of CO2 variation can be assessed. Hydrosphere [to be inserted (CEH)] Lithosphere A static (but variable) representation of continental configuration (and elevation ?) and ocean bathymetry should be adequate. Variable effects of precipitation on erosion and Calcium dissolution need to be included to close the Calcium/Carbonate/sediment accumulation cycle. NB: The acquisition of suitable palaeo-data from the geological record is a vital part of the overall project, but not part of the model construction per se. Overall In all of the above modules, it should (so far as possible) be possible to switch key processes on and off, in order that (numerous) alternative simulations can be run to determine the relative importance of each process.. The model needs to be capable of running for several hundred thousand years at least, for each of a large number of scenarios. With the degree of spatial resolution outlined above, there would be around one thousand grid points in the atmosphere and the ocean, compared to several million in GCM-based climate models. Great care will be needed to parameterise sub-grid scale processes adequately, and this represents a major challenge. It is not clear whether or not seasonal processes will need to be represented explicitly. If they do, then time-steps of less than one year will be needed, and computational speed is likely to be a serious limiting factor. If they can be parameterised effectively, much longer time-steps mat be achievable, allowing considerable elaboration of other aspects of the model. D) Resources It is suggested that the model should be highly modular, (possibly with a NERC Centre/Survey or University group taking lead responsibility for each module). As a first guess, it should be possible for prototypes of each module to be constructed by a few people (mostly post-docs or equivalent) working for a few years. The scale of the initial development project, including a synthesis and interface teams, co-ordination and project management and hardware (workstations, etc.) is therefore of the order of £1M per annum for (say) 5 years. Access to supercomputer facilties may also be required during the later stages, especially for sensitivity testing, estimation of confidence limits, etc. It is possible that some external funding (or at least co-funding) might be secured (DoE ?). The project does not easily fit into any of the categories of NERC's present Funding Model. If successful, it should probably evolve in due course into a joint collaborative core-strategic programme between the Centres/Surveys and the other institutions involved. These would include SOC, BAS, CEH, CCMS, BGS, UEA, UGAMP/CGAM (Reading) and the Hadley Centre. The development work can be carried out in a distributed but highly co-ordinated manner, and may probably thus best be treated as a "consortium" project, rather than a thematic programme. A core team (including probably the synthesis and interfacing teams) will be required at one location, and the possibility of secondments and joint appointments of staff at other sites should be considered as a possible mode of operation. The people involved would all require good mathematical/computational skills, and appropriate appointments might therefore be to fellowships similar to those available under the existing conversion scheme for physicists and mathematicians. John Shepherd Southampton Oceanography Centre 10 December 1998 Attachment Converted: "c:\eudora\attach\Mmesm.doc"