Title:	Simulations with earth system model EC-Earth
DNr:	NAISS 2025/2-4
Project Type:	NAISS Large Storage
Principal Investigator:	Qiong Zhang <qiong.zhang@natgeo.su.se>
Affiliation:	Stockholms universitet
Duration:	2025-07-01 – 2026-07-01
Classification:	10501 10508 10509
Homepage:	https://www.su.se/english/profiles/qzhan
Keywords:

Abstract

Our group is utilising the Earth System Model EC-Earth to conduct climate model simulations of past climates, enabling us to study the climate system's response to various climate forcings that differ from present and historical periods. These simulations provide crucial information on past climate changes, which can help assess the credibility of climate projections for future climate change. Over the past few years, we have conducted core experiments of PMIP4/CMIP6, consisting of five time-slice simulations and a transient simulation. Four experiments have been completed, and the data has been published on ESGF, contributing to CMIP6 and IPCC AR6. However, we have encountered issues with one time-slice experiment for the Last Glacial Maximum (LGM) due to model crashes at extremely low temperatures. Investigations and tests are ongoing to address this issue. As part of our VR grant on ‘Simulating the green Sahara with an Earth System Model,’ we have completed a long-term transient simulation using EC-Earth-VEG-LR, investigating the model's ability to replicate an abrupt ecosystem regime shift that occurred during the mid-Holocene. The 8000 years long simulations show a significant change in the climate system around 5.5 ka. We are diagnosing what processes are responsible for this change. We suggest the interplay between climate-vegetation-ocean feedback playing roles in generating this variability during the Holocene. In our Holocene transient simulation and long PI control runs, we have observed a significant centennial variability. To better understand the physical mechanisms behind this variability, we are conducting ensemble simulations by starting the simulation from different phases of AMOC to investigate how does it affect the low-frequency variability in the climate system. Our team's previous research, which incorporates proxy data and multi-model paleoclimate simulations, reveals that the mid-Pliocene hydroclimate state is influenced not by direct CO2 radiative forcing, but by long-term Earth system feedback resulting from elevated CO2 levels. Understanding these slow feedbacks is crucial in studying the climate's response to fluctuating CO2 levels, as they can significantly amplify surface temperature changes. For our planned simulations, we will continue to use HPC resources through the Bolin Centre for Climate Research project, specifically through NAISS 2024/2-1 and SMIP proposal 2024/1-12. We will also use storage in the NAISS 2025/2-4 proposal to continue NAISS 2024/2-2, as the large amount of data generated from our simulations require significant storage space. Our research aims to advance our understanding of the climate system's behaviour and how it has responded to past climate changes. By studying these past climate changes, we can make more informed predictions about future climate change and its potential impacts.