Paola A. Arias Professor, Universidad de Antioquia, Medillín, Colombia

Title: How well do CMIP6 models simulate key boundary conditions affecting South American climate? Insights for regional modelling efforts

Abstract: South America is a large continent with a wide diversity of weather and climate features, including tropical, subtropical and extratropical regimes interacting within a complex landscape. Simulations by global climate models, as well as their downscaling through regional circulation models or statistical methods, are important tools, particularly when assessing the impacts of climate change in the continent. This work evaluates 57 models of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) in their simulation of various spatial patterns and circulation features over South America. Our evaluation aims to provide useful input for the selection of climate models to force regional simulations in South America. Therefore, we focus on spatial fields that are relevant for regional simulations, such as horizontal winds, sea level pressure, sea surface temperature (SST), and moisture and energy fluxes across the domain boundaries. Additionally, we evaluated different circulation features influencing the regional climate of South America that have not been widely evaluated in these models. Several indices are studied to assess the main low-level and upper-level continental-scale circulation patterns, the regional Walker and Hadley cells, the subtropical highs and the boundary SST patterns. Our results show that no single model performs best across all evaluated features, highlighting the importance of in-depth model evaluation for the region concerning the features of interest.

Claudia Tebaldi Scientist, University of Maryland, USA

Title: Emulators of Earth system model output, an overview

Abstract: Researchers’ and decision-makers’ demand for climate information has outpaced the ability of computationally intensive Earth System Models (ESMs) to provide targeted climate projections, particularly when specific output for specific needs is required. Emulators of ESMs —significantly more efficient computationally — aim to produce such information and have seen an accelerated period of development. Emulators’ latest generation greatly varies in method, complexity, requirements, and outputs. Some emulators produce only patterns of average quantities, targeting climate responses to anthropogenic forcings. Others simulate quantities at high temporal and spatial frequency, accounting for the climate system internal variability. In this talk I’ll give a brief summary of a recent review paper I lead. I’ll aim to discuss what we identified as the main categories of emulators; how a choice of emulator, based on different methods, inputs, and outputs, might or not be fit for purpose, to support climate and sustainability science and applications. I will conclude by mentioning gaps and research needs informing future developments.

Gopika Suresh PhD Research Scholar, National Institute of Oceanography (CSIR), Goa University, Goa, India

Title: Drivers of Future Indian Ocean Warming and Its Spatial Pattern in CMIP Models

Abstract: Coupled Model Intercomparison Project phases 5 and 6 (CMIP5/6) projections display substantial inter‐model diversity in the future tropical Indian Ocean warming magnitude and spatial pattern. Here, we investigate the underlying physical mechanisms in 46 CMIP5/6 models using an upper‐ocean heat budget framework that separates surface net air‐sea flux changes into forcing and feedback components. The multi‐ model mean (MMM) basin‐averaged warming is primarily driven by reduced evaporative cooling due to weaker surface winds related to reduction of both summer and winter monsoonal circulations and increased near‐surface relative humidity, with inter‐model variations in these parameters controlling warming diversity. The MMM warming pattern features a weakening equatorial gradient, resembling a positive Indian Ocean Dipole phase, and a strengthening interhemispheric gradient, both of which also dominate inter‐model spread. Ocean dynamics modulate the amplitude of the MMM IOD‐like pattern and its inter‐model variability through the Bjerknes feedback, which couples the zonal equatorial SST gradient, equatorial winds, and thermocline slope. Interactions with the tropical Pacific may further contribute to this response. Meanwhile, stronger climatological winds enhance evaporative cooling in the Southern Hemisphere, reducing warming there, and strengthening the MMM interhemispheric SST gradient. The diversity in this interhemispheric gradient is linked to variations in cross‐equatorial wind changes and their impact on latent heat flux forcing. This interhemispheric gradient strengthening is part of a broader pan‐tropical pattern, with similar features in the Pacific and Atlantic Oceans. These findings clarify the relative roles of thermodynamic processes and ocean dynamics in shaping future tropical Indian Ocean warming.