PAlaeo-Constraints on Monsoon Evolution and Dynamics

Lead Research Organisation: University of Reading
Department Name: Geography and Environmental Sciences

Abstract

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 (MH, 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 palaeo-constraints that can be used to assess the reliability of future monsoon evolution.

Planned Impact

Practical Impact on Climate Services. PACMEDY will deliver an assessment of how well state-of-the-art climate models, the models that are used to make projections of near-term climate changes and form the basis of the projections made by climate services, represent climate conditions outside the modern range. By combining model results and palaeo-observations, it will provide a set of new constraints on the realism of representation of tropical hydrologic budgets. Such assessments, at the very least, provide information that allows climate services to define the level of uncertainty inherent in any projections that are to be used for planning purposes. However, PACMEDY intends to go beyond this by working with the climate services to develop ways in which identified biases and key uncertainties at different timescales can be factored into the provision of regional projections. Fusing the strengths of state-of-the-art modeling and palaeoclimate constraints should provide more realistic projections and a better foundation for planning.

Policy Impact. The development of climate mitigation policies strongly depends on the availability and reliability of climate projections. The development of climate adaptation policies is strongly dependent on these projections and on the climate services they provide. The timeframe for adaptation actions can range from years to decades, and knowledge of the uncertainties inherent in projections on this timeframe is crucial. Nearly half the world is dependent on monsoon precipitation, and many of these countries are particularly vulnerable to climate change. PACMEDY will deliver an improved understanding of monsoon dynamics, measures of the reliability of projections in the tropics, approaches to improve the characterization of future monsoon evolution, and an assessment of the likelihood of extreme droughts and flood. We will ensure that this information is made available to policy-makers in a timely fashion. We will work with policy-related organisations both at a national level (e.g. LWEC in the UK, Brazilian Interministerial Committee on Climate Change) and at a international level (e.g. via the Intergovernmental Panel on Climate Change, IPCC and the Intergovernmental Platform on Biodiversity and Ecosystem Services, IPBES).

PACMEDY will deliver results in time for the next IPCC Assessment Report. Our results will contribute both to Working Group 1 (the Scientific Basis) since we will address the issue of how the changes in mean climate and modes of variability affect tropical climates. They will also contribute to Working Group 2 (Impacts, Adaptation and Vulnerability) since they will address regional monsoon changes and feedbacks and extreme events in the African, Indian, East Asian and South American monsoon regions. The use of detection/attribution methods will also provide new information of the role of different forcing factors at these regional scales. Several participants were engaged in the previous IPCC assessment and expect to make a contribution to the next Assessment.

PACMEDY will also deliver information about ecosystem responses to long-term climate change and IM variability, and this will assist in assessing the likely impact of future changes on natural vegetation, ecosystem services and biodiversity. This work will contribute to the report of the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES).

The work in WP4 of the PACMEDY project and stakeholder conference planned in the final year of the project (see below) are designed to produce and highlight results have direct policy relevance for long-term planning.

Publications

10 25 50
 
Description We have shown that model predictions of changes in monsoons in the past are substantially underestimated by state-of-the-art climate models, and that these models are therefore likley to underestimate the magnitude of change in the future.

Speleothem isotopic records provide coherent regional signals of climate change in monsoon regions. There ia a strong impact of global temperature on glacial-interglacial timescales, but precipitation, recycling and changes in source area are more important on millennial timescales. The identification of coherency in the signals is possible because of the extensive compilation of isotopic data undertaken by the SISAL working group and coordinated through this project.

The underestimation of monsoon changes has been a persistent problem for climate models. Analysis of the latest generation of models, undertaken in this project, shows that the mismatches are not improved. The implication of these findings is that current models are highly likely to underestimate future changes in monsoon regions.

Both tree ring and speleothem isotopic records have been used to reconstruct interannual variability in climate. Our investigations of tree ring records from northern extratropical regions shows that the interannual variability of stem growth is muted compared to the interannual variability of climate because of changes in carbon allocation to above- and below-ground components of the tree, and because of carbon carry-over between years. Thus these records underestimate interannual climate variability.
In a similar way, speleothem isotopic records are smoothed because of the variable time lag between precipitation events and incorporation in the speleothem itself. Best matches between observed 18O and speleothem 18O globally are obtained using decadal smoothing. Both these investigations indicate that tree rings and speleothem isotopic records should only be used with caution to investigate changes in short-term variability.

As part of the project, we have developed a process-based model to relate changes in speleothem carbon isotopic records to climate and vegetation processes operating above the cave. We have shown that a large part of the change recorded by speleothem carbon isotopes on glacial-interglacial timescales is a result of the direct impact of changes in atmospheric CO2 on plant productivity and drought-induced changes in stomatal conductance. Vegetation changes, specifically shifts between C3 and C4 vegetation, are important for interpreting changes on millennial timescales.
Exploitation Route (1) Improvement of climate models
(2) Use of uncertainties to determine future impacts on hydroclimate and water resources
(3) Use of forward modelling tools to interpret speleothem isotopic records
(4) use of palaeoclimate databases assembled in the project for model evaluation and benchmarking
Sectors Agriculture, Food and Drink,Energy,Environment

URL https://pacmedy.lsce.ipsl.fr/wiki/doku.php
 
Title BIOME 6000 DB classified plotfile version 1 
Description Provides a file with vegetation reconstructions for the LGM and MH using a standardised classification 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact Has already been downloaded more than 70 times by parties wishing to use it 
 
Title Modern pollen data for climate reconstructions, version 1 (SMPDS) 
Description The dataset contains percentage counts for the 247 most important European pollen taxa from individual modern samples from Europe and northern Eurasia, and supporting metadata about each sample. The dataset has been specifically designed for use for quantitative climate reconstructions. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Title SISAL (Speleothem Isotopes Synthesis and AnaLysis Working Group) database Version 1.0 
Description Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The first version of the SISAL database contains oxygen and carbon isotope measurements from 371 individual speleothem records, and 10 composites from 174 cave systems worldwide, and metadata describing the cave settings and age models of these records. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
 
Title SISAL (Speleothem Isotopes Synthesis and AnaLysis Working Group) database version 1b 
Description Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. Version 1b of the SISAL database contains oxygen and carbon isotope measurements from 440 individual and 15 composite speleothem records from 221 cave systems worldwide, as well as metadata describing their cave settings and age-depth models. New records have been added and some metadata has been amended. The SISAL working group has also created SISAL chronologies for 20 entities, all of which had no published chronologies. In order to assure traceability, any presentation, report, or publication that uses the SISALv1b database should cite Atsawawaranunt et al. (2018) (The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems; https://doi.org/10.5194/essd-10-1687-2018) and Comas-Bru et al. (2019) (Using speleothem records of climate changes since the last glacial for model evaluation; submitted to Climate of the Past). If using individual sites or speleothems, the literature citations for published work provided in the database should also be cited. Contact information of data contributors of unpublished data is also provided and these should be contacted when unpublished records are used on an individual basis. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Title Python translation of KarstFor model 
Description Python translation of the KarstFor speleothem model by Baker et al. [2012]. This program is currently set up to take input from model output of the SWINGS2 intercomparison [Risi et al., 2012]. 
Type Of Technology Software 
Year Produced 2018 
Impact N/A 
URL https://osf.io/bvu6m/
 
Description Interview with investors 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Shared information about large uncertainties associated with hydrological change in monsoon regions under climate change
Year(s) Of Engagement Activity 2019
 
Description Stakeholder meeting, Pune 18-19th March 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Stakeholder meetings around the theme of climate change and impacts on hydrology, biodiversity and agriculture. We shared the results from our project on uncertainties in regional predictions of monsoon rainfall.
Year(s) Of Engagement Activity 2020