Abstract
Abstract. We investigate the climate impact of reduced dust during the mid-Holocene using simulations with the IPSL model. We consider simulations where dust is either prescribed from an IPSL PI simulation or from CESM simulations (Albani et al., 2015). In addition, we also consider an extreme mid-Holocene case where dust is suppressed. We focus on the estimation of the dust radiative effects and the relative responses of the African and Indian monsoon, showing how local dust forcing or orography affect atmospheric temperature profiles, humidity and precipitation. The simulated mid-Holocene climate is statistically different in many regions compared to previous mid-Holocene simulations with the IPSL models. However, it translates to only minor improvements compared to palaeoclimate reconstructions, and the effect of dust has little impact on mid-Holocene model skill over large regions. Our analyses confirm the peculiar role of dust radiative effect over bright surfaces such as African deserts compared to other regions, brought about by the change of sign of the dust radiative effect at the top of atmosphere for high surface albedo. We also highlight a strong dependence of results on the dust pattern. In particular, the relative dust forcing between West Africa and the Middle East impacts the relative climate response between India and Africa and between Africa, the western tropical Atlantic and the Atlantic meridional circulation. It also affects the feedback on the Atlantic Ocean thermohaline circulation. Dust patterns should thus be better constrained to fully understand the changes in the dust cycle and forcing during the mid-Holocene, which also informs on the potential changes in key dust feedbacks in the future.
Highlights
The mid-Holocene climate is a long-standing focus in the Palaeoclimate Modelling Intercomparisons Project (Joussaume and Taylor, 1995; Kageyama et al, 2018)
– How the reference dust used in different models when running mid-Holocene simulations affects the results. We address this here by comparing simulations using Albani’s reference dust (Otto-Bliesner et al, 2017) instead of the pre-industrial (PI) dust field simulated with the INCA-Institut Pierre Simon Laplace (IPSL) model (Lurton et al, 2020)
We analysed the impact of dust reduction on the midHolocene climate considering both an extreme case where dust is suppressed and a mid-Holocene dust reduction from interactive dust–climate simulations following the PMIP4 dust protocol (Otto-Bliesner et al, 2017)
Summary
The mid-Holocene climate is a long-standing focus in the Palaeoclimate Modelling Intercomparisons Project (Joussaume and Taylor, 1995; Kageyama et al, 2018). Despite the different points of view, the results raised several questions on the dust–climate interactions and the way the response depends on the land surface conditions, with evidence that vegetation or lake cover play a role on dust emissions and on the radiative effect of dust and thereby on the atmospheric circulation and monsoon precipitation (Egerer et al, 2018; Messori et al, 2019; Pausata et al, 2016) They raise questions on how the different representations of dust in climate models impact the magnitude of the dust feedback on mid-Holocene precipitation (Hopcroft and Valdes, 2019).
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