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|Assessment of modelling uncertainties in long-term climate and sea- level change projections|
Original title: Bepaling van onzekerheden in modelprojecties van het klimaat en het zeeniveau op lange termijn
Parent project: Science for a Sustainable Development
Reference no: SD/CS/01A
Period: December 2005 till January 2010
Policymakers are facing a wide range of possible scenarios for long-term climate and sea level evolutions without knowing precisely why they differ and how reliable they are. Two factors explain this wide estimated range: uncertainties in the future anthropogenic emissions of greenhouse gases and aerosols, and uncertainties in the understanding and modelling of the processes that influence climate. Under these circumstances, it is difficult to know which decision should be taken to avoid the most dramatic effects of climate change. However, decisions should be taken in a very near future because we could possibly pass some threshold that would lead to irreversible changes.
The overall objective of ASTER is to identify a range of possible climate and sea level change scenarios over the next three millennia that are coherent with the past evolution of the Earth system in order to get some insight on uncertainties in the modelling process and to understand the causes of this range of projections.
We will vary some key physical parameters of LOVECLIM, a global three-dimensional Earth system model of intermediate complexity, within their range of uncertainty in order to construct about 30 different model versions resulting in contrasted climate, sea level and CO2 atmospheric concentration responses to changes in forcing. This approach has been chosen because it is cheap in term of computer time and because, using a restricted number of model versions will allow a better knowledge of the characteristics of each version. For each set of parameter values, three types of experiments will be conducted, i.e. a long control experiment under pre-industrial conditions, a freshwater hosing experiment to assess the stability of the North Atlantic meridional overturning circulation and an experiment in which the CO2 concentration will be quadrupled to have a clear and strong climate signal.
The selected model versions, which should all yield a reasonable control climate, will then be utilized to carry out transient experiments over the Holocene, with a particular focus on the period around 8200 year before present, i.e. at a time of an abrupt climate change event, and the last millennium. In a last step, we will select the model versions that show the best agreement with the available reconstructions of past climates and tracer distributions, and we will employ them to perform climate and sea level change projections over the next three millennia under various CO2 emission scenarios.
Interactions between the different partners
Each partner (UCL, VUB and ULg) carries out model improvements in his/her field of expertise in order to build a basic ‘ASTER’ model. UCL will develop an automatic procedure for set-up of the simulation and post-processing of the results and will design a test of the ability of the models to simulate specific climate situations.
The partners choose together the parameters of the model that will be at the base of the various versions, on the basis of result of three types of experiments (long pre-industrial equilibrium, quadrupling of the CO2 concentration, water hosing in the North Atlantic). VUB, ULg and UCL conduct the simulations specific to the project, i.e. 8200 year event, the Holocene and the last millennium, respectively. This work is distributed amongst the partners, but each partner performs the analyses related to his/her field of expertise for all the experiments. Regular meetings allow a thorough discussion of the results.
Link with international programmes
The objectives of ASTER perfectly meet those of the Global Change and Ecosystem Programme of the European Union’s Framework Programmes, the World Climate Research Programme (WCRP), in particular its core projects Climate and Cryosphere (CliC), Climate Variability and Predictability (CLIVAR), and Coordinated Observation and Prediction of the Earth System (COPES), the International Geosphere-Biosphere Programme (IGBP), especially its core projects Past Global Changes (PAGES) and Surface-Ocean-Lower Atmosphere Study (SOLAS), and the core project Antarctic Climate Evolution (ACE) of the Scientific Committee on Antarctic Research (SCAR). It is worth mentioning that ASTER partners actively participate in those research programmes. ASTER is complementary to the European projects MOTIF (Models and observations to test climate feedbacks) and ENSEMBLES (Ensemble-based predictions of climate changes and their impacts) The former version of the model was employed in the previous assessment reports of the Intergovernmental Panel on Climate Change (IPCC). ASTER results will undoubtedly be part of the IPCC Fifth Assessment Report.
Expected results and/or products
On the scientific point of view, the main deliverables of ASTER will consist of an improved version of LOVECLIM; it will also identify a selection of set of parameters leading to an ensemble of model versions showing a large range of responses to prescribed forcings; it finally will present a detailed study on the model response to increased CO2 concentration and freshwater perturbation.
Apart from the scientific benefits, the project will provide policymakers with long-term projections of climate and sea level changes with increased confidence. This should help the decision-making process regarding reduction in future CO2 emissions and adaptation to climate and sea level changes. Additionally, the model outputs will be useful for a number of follow-up projects in the climate impact research community, for example, for studies dealing with agricultural productivity, human health and socio-economical aspects of climate change.
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