The HOTCLIM Make Our Planet Great Again project

Summary
The MOPGA HOTCLIM project (2020-2025) studies the variability of the climate of high latitudes during past warm periods, which present a polar warming comparable to that projected by 2100 due to specific combinations of orbital forcings and atmospheric CO2 concentration. It is based on an approach combining gas analyzes on the air trapped in ice cores drilled in Antarctica, syntheses of climatic data from glacial, marine and land archives, and a comparison with the results of climate models. The HOTCLIM project will improve our understanding of (1) the natural variability of climate under orbital and CO2 forcing, and (2) the response of the polar caps, sea level and ocean circulation to prolonged warming. It will provide benchmarks to test the performance of climate models outside of the short-term climate observation range and within a range of temperature changes comparable to projected future warming, thus helping to improve climate projections.

Context
Many uncertainties remain about future and past interactions between climate and the carbon cycle, as well as their impact on the components of the Earth system, particularly those that are most sensitive to a warming climate (eg ice caps, sea level, ocean circulation). Progress on this subject requires compensating for the lack of data on hot climates, which are nevertheless essential in order to (1) describe climate change around the globe, (2) determine variations in atmospheric CO2 concentration and identify its sources of emissions, and (3) identify the sensitivity of the climate to CO2 forcing as well as to other factors (eg orbital forcing, ice volume, freshwater flux).

Objectives
The Make Our Planet Great Again HOTCLIM project (Characterisation & Dynamics of Past Warm Climates, 2020-2025), carried by Emilie Capron within the iCe3 team, focuses on the study of so-called interglacial periods of the past. These interglacials are characterized by a wide range of warm conditions at the poles, i.e. comparable to today or the simulated warming for the end of the century in these regions, due to specific combinations of orbital forcings and atmospheric CO2 concentration.
The objective of the HOTCLIM project is to characterize and better understand the phase relationships between radiative forcing, the carbon cycle, and climate and ice sheet responses during interglacials of the last 450,000 years. For this, it is based on :
– * Measurements of the atmospheric concentration of CO2 on the Antarctic core EPICA Dome C to constrain the dynamics of the carbon cycle and its link with the climate (see project of the HOTCLIM thesis, E. Legrain, 2020-2023) ;
– * The development of the air content measured in the ice as a tool to constrain the absolute dating of ancient ice, necessary to understand the link between orbital forcing, CO2 and climate ;
– * The integration of information from ice with that from marine and terrestrial archives via climatic data compilations based on a common and rigorous chronological framework ;
– * Model-data comparison exercises in order to test and identify the mechanisms and feedbacks in play between radiative forcing, climate and ice volume

Expected results
The HOTCLIM project will quantify the magnitude of warming at high latitudes and the links with the carbon cycle and orbital forcing under warm conditions. This will provide a better understanding of the response of the polar caps, sea level and ocean circulation to prolonged warming. The HOTCLIM project will also place future climate change in the context of natural climate variability. Finally, it will provide benchmarks to test the performance of climate models outside the range of short-term climate observation and in a range of temperature changes comparable to the expected future warming, thus helping to improve climate projections.

Collaborations
The HOTCLIM project is based on strong collaborations within the iCe3 team at IGE. Close collaborations at the national level are also envisaged, in particular with A. Landais (isotopes of air trapped in ice), A. Govin (marine sediments) and N. Bouttes (climate modeling) of LSCE. At the international level, strong links exist with the European H2020 BE-OI project (2019-2025) and the ITN DEEPICE network (2021-2025).