JCLI - JCLI

PAlaeo-Constraints on Monsoon Evolution and Dynamics – PACMEDY

PACMEDY

This project uses annually-resolved palaeoenvironmental records of climate variability over the past 6000 years from corals, molluscs, speleothems and tree rings, together with global climate-model simulations and high-resolution simulations of the Indian, Africa and South American monsoons, to provide a better understanding of monsoon dynamics and interannual to multidecadal variability (IM).

The global objectives of the project are to provide improved projections of monsoon behavior and extreme events based on knowledge of the past.

Some difficulties arose from the late signature of the consortium agreement which delayed the work for some of the partners. On the scientific side, the new palaeoclimate simulations that will be run as part of CMIP6 will be delayed due to an overall shift in the international calendar for these simulations. Therefore some the groups in charge of running these simulations are only starting them. It concerns the simulations planned for the mid-Holocene and the last millennium. To overcome this difficulty the analyses will consider simulations that are available as part of CMIP5 and PMIP3. A stronger focus will also be put on transient Holocene experiments. The new simulations will be included as soon as they are available, so that the project can still provide new model evaluations in time to be considered by the lead authors of the IPCC AR6 report. On the data side there is a slight delay in the provision of some of the data set in international data base concerning speleothem for south America, or India, but a specific PACMEDY entry will be created in these databases, so that the project can benefit from all the available data sets and contribute to the international effort.

For the next periods, the first objective is to have the synthesis completed and the CMIP5 mid Holocene and last millennium simulations launched. We can expect that that the new simulations will be available by the end of the year. A focus will be put on the tropical rain belt over the ocean and the monsoon regions and how its variability is affected by changes in interannual to multidecadal variability. Methodological aspects will be considered for the identification of these modes in the different reconstructions and simulations. Metrics will be developed for model evaluation, taking into account when possible the fact that systematic model biases in model climatology affect some of the changes and regional comparisons. Forward modelling will be used to define evaluation criteria.

The major results reflecting collaborative work between the groups concerns the ongoing data synthesis for speleothem and the connection with the PAGES SISAL working group. PACMEDY is on the good track to fully contribute to the South American and Asian synthesis. The synthesis will also provide unique indication of decadal variability in these regions for the second half of the project.

The other significant advance concerns the transient Holocene simulations by MPI and LSCE that will open a new framework for model-data comparisons for the second half of the project, during which these simulations together with the different sensitivity experiments and forward modelling will help us to decipher the role of the long term insolation forcing and of the feedbacks from vegetation or dust on the Holocene climate trends, variability and extreme droughts or dry spell in monsoon.

The next period will go for the publications of the different reconstructions and the major climate simulations. The work will be organised around the 3 monsoon regions, so as to put in a common framework the results of the reconstruction (long term and variability) and of the climate simulations (global, regional). A more global approach will also be developed to connect tropics and extratropical climate. For all the analyses the three questions raised in WP4 on emerging constraints, the credibility of climate simulations and a quantification of the risk of extreme monsoon depending on the climate background state will be investigated. The work will be organised though regular visios between partners involved in same regions.
In the coming months particular attention will be put on :
- The comparisons of climate reconstructions from different archives in the same regions, considering the Indian sector and the Pacific/Indonesian sector
- The comparisons of the long term variability extracted from speleothems in South America and in the Indian sector to isolate the relevant time scales and major event with which we’ll be able to compare these records with model outputs
- The identification of the different factors and metrics to be considered in WP4 for the 3 monsoons and their teleconnexions.

Several publications have been pproduced
5 including multi-partners
3 including only French Partners
6 including only foreign partners

Several presentation at international conferences have also be done.
cd details in the report

Monsoon systems influence the water supply and livelihoods of over half of the world. Observations are too short to provide estimates of monsoon
variability on the multi-year timescale relevant to the future or to identify the causes of change on this timescale. The credibility of future projections of
monsoon behavior is limited by the large spread in the simulated magnitude of precipitation changes. Past climates provide an opportunity to
overcome these problems. This project will use annually-resolved palaeoenvironmental records of climate variability over the past 6000 years from
corals, molluscs, speleothems and tree rings, together with global climate-model simulations and high-resolution simulations of the Indian, African,
East Asia and South American monsoons, to provide a better understanding of monsoon dynamics and interannual to multidecadal variability (IM).
We will use the millennium before the pre-industrial era (850-1850 CE) as the reference climate and compare this with simulations of the mid-
Holocene (6000 years ago) and transient simulations from 6000 year ago to ca 850 CE. We will provide a quantitative and comprehensive
assessment of what aspects of monsoon variability are adequately represented by current models, using environmental modelling to simulate the
observations. By linking modelling of past climates and future projections, we will assess the credibility of these projections and the likelihood of
extreme events at decadal time scales. The project is organized around four themes: (1) the impact of external forcing and extratropical climates on
intertropical convergence and the hydrological cycle in the tropics; (2) characterization of IM variability to determine the extent to which the
stochastic component is modulated by external forcing or changes in mean climate; (3) the influence of local (vegetation, dust) and remote factors on
the duration, intensity and pattern of the Indian, African and South American monsoons; and (4) the identification of paleo-constraints that can be
used to assess the reliability of future monsoon evolution.

Project coordinator

Madame Pascale BRACONNOT (Laboratoire des Scences du Climat et de l'Environnement)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CNRS DR IDF SECTEUR PARIS B CNRS DR IDF SECTEUR PARIS B
IAP Institute of Atmospheric Physics, Chinese Academy of Sciences
Institute of Astronomy, Geophysics and Atmospheric Sciences
AWI Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research
University College London
University of Edinburgh
HZG Helmoltz-Zentrum Geesthacht
LPGNantes - Université de Nantes Laboratoire de Planétologie et Géodynamique de Nantes - Université de Nantes
Max Planck Institute for Meteorology
Stockholm University
EPOC Environnements et Paléoenvironnements Océaniques et Continentaux
LOCEAN Laboratoire d'Océanographie et du Climat: Expérimentations et Analyses Numériques-IPSL/Pierre et Marie Curie University
ISEM Institut des Sciences de l'Evolution de Montpellier
CNRS DR12 - CEREGE Centre National de la Recherche Scientifique Délégation Provence et Corse - Centre Européen de Recherche et d'Enseignement en Géoscience de l'Environnement
IITM Indian Institute of Tropical Meteorology
CNRS-LSCE Laboratoire des Scences du Climat et de l'Environnement
University of Reading

Help of the ANR 531,552 euros
Beginning and duration of the scientific project: May 2016 - 36 Months

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