Causes and timing of Himalayan glacier fluctuations during the Holocene – CIME

CIME focuses on the evolution of WCH glaciers during the Holocene. It gathers a unique multidisciplinary science team and builds on the latest developments in past glacier exploration from moraines, making use of the most up-to-date dataset of chronologies, with most accurate present-day observations, and glacier monitoring, and new glacier and climate modelling.
CIME is organized in 5 WPs from the current glacier-climate relationship to the paleo-glacier modelling. The WP1 is devoted to the management. Then the project relies on an integrated approach combining a detailed analysis of present surface mass balance and associated climate drivers (WP2). WP3 is devoted to Holocene moraine records from 40 glaciers and their dependence on the geomorphological context. WP4 explores new investigations (including new climate simulations) on high-altitude paleo climate conditions with a special focus on ASM. WP5 investigates long-term glacier-climate relationships and different glacier trajectories based on statistical and glaciological approaches. All together these findings will help identify most sensitive glaciers.
The core of CIME’s strategy focuses on sites in India, Nepal and Bhutan where glaciers are largely driven by ASM and also by temperature for several reasons. These three target regions (India, Nepal and Bhutan) make it possible to investigate past glacier climate relationships, from pure ASM-influenced glaciers to transitional cases influenced both by the ASM and the Westerlies, in a context where recent mid to late Holocene simulations and speleothem records suggest a reduced monsoon activity, but increased monsoon variability with time.

First field trip in winter 2025

The impacts of the project can be summarized as follows: A) ASM is the engine of the regional climate conditions in WCH. Thus new knowledge on ASM will help to improve high altitude climate reconstructions and predictions, which are useful for cryosphere sciences (glacier, snow) and direct societal implications (hydrology, agriculture, risks). Results will also be beneficial for scientists working on lower lands of WCH helping the understanding of extreme floods and droughts or other environmental changes. ASM also plays a key role in global climate and thus our results will help scientists working not exclusively on WCH. Importantly, the new high-resolution climate model outputs (IPSL) will be performed with different sensitivity analyses that will be given to the international community; B) our investigations will propose an holistic methodology based on moraines, surface area and mass balance, glacier trajectories over the Holocene with their specific climate conditions. This holistic framework could be transferred to other regions. More specifically the chronologies will be based on an improved 10Be/14C methodology which is for the first time applied in HMA. The non-stationarity of the glacier type (DF or DC) through time has never been considered so far in the future predictions, while our preliminary investigations33 revealed some changes existed in the past with DF evaluating towards DC glaciers during the Holocene. Thus, CIME will help to better constrain glacier evolution. CIME will help to list the very sensitive glaciers in WCH to climate change. This index could help to diagnose the best-case studies for future glaciological investigations in HMA. Revealing that DF and DC glaciers had a similar response to climate change over the last 6 ka would help comfort/refute future estimations based short time period of glacier modelling. By using such an approach combined with glacier modelling we will reveal if current glacial retreat is un precedent in the Holocene as already observed in the tropical Andes. Here again the methodology could be used for other regions; C) the modelling approach will offer an holistic approach for the scientific community: i) a new OGGM package for past glacier modelling particularly adapted to mountain glacier changes at a regional scale over 11.6ka; ii) facing discrete moraine issues this new methodology could be applied to all other records from the international database ICE-D.The new R package will be given to the scientific community at the end of the project.

in progress

Determine the impact of natural climate variability on the evolution of Himalayan glaciers is crucial regarding their current retreat and their future. Past glacial extents from moraines records make it possible to identify associated climatic forcings. We will document the Holocene evolution of 40 glaciers located in India, Nepal and Bhutan and determine the respective part of the associated climatic forcings and the geomorphological context.
The project is structured into 5 WPs, the first being intended for the organization and dissemination of knowledge. WP2 focuses on the current functioning of the 40 glaciers and the local climate based on ERA 5 reanalyses coupled with statistical downscaling to then calibrate the OGGM glaciological model. In WP3 we study the Holocene evolution of the 40 glaciers from moraines dated with cosmogenic isotopes. Comparisons between glaciers will make it possible to measure the influence of climate and geomorphology. In WP4, climate variations and associated forcing will be described based on downscaled outputs from climate models including new simulations of the IPSL model combined with other already available output runs from TraCE, HADCM3 et LOVECLIM. Zoomed runs with sensitivity tests will be carried out to analyze the role of forcing. A model - data comparison will be carried out in order to better constrain the associated uncertainties.

In WP5 we will propose annual trajectories of glacier evolution either by forcing OGGM with climatic outputs whose relevance will be tested from moraines or from statistical modeling independent of GCMs. At the same time, temperature-precipitation pairs determined from the equilibrium line will be compared to the values of the climate models. An index will be proposed to identify the best glaciers, preferred targets for studying their response to climate and its impacts on sea level and hazards.
This project is based on four French laboratories: CEREGE, IGE, LSCE, and Epoch, with partners in India and Nepal. Particular attention will be paid to the transmission of the scientific findings of this project to a broader audience in France and abroad. Several axes are proposed in addition to scientific articles and conferences at international conferences, including the production of a film, a summer school, and a collaborative science project with scientific teachers from a 6th class of high school. In the field, gender balance and the participation of students from partner universities will be ensured to promote the transmission of knowledge.