Abrupt climate change in the North Atlantic: the subpolar gyre circulation as a tipping element of the climate system
Ocean Sciences, Climate
Research area
The scientific context of my thesis work is that of climate tipping points (CTPs). The risk CTPs. The dramatic impacts associated with CTPs are making them a growing research topic and source of public concern. CTPs occur when change in part of the climate system (tipping element) becomes self-perpetuating beyond a warming threshold as a result of asymmetry in the relevant feedbacks, leading to substantial and widespread Earth system impacts. At the state of the art, five tipping elements have been listed as already susceptible to cross tipping points at the current level of warming of ∼1.1°C above pre-industrial, including the potential collapse of the North Atlantic Subpolar Gyre (SPG) deep convection. Despite existing dynamical interpretations, a comprehensive understanding of the mechanisms behind convection shutdown remains incomplete, requiring addressed studies combining observations and climate models based information.
Project goals
The goal of my project is to better understand the mechanisms leading to the shutdown of Subpolar Gyre (SPG) deep convection, both in a stable climate and under global warming. To this end, so far I have been investigating preindustrial control simulations of climate models contributing to the Climate Model Intercomparison Project; the goal for my next months is to extend the analysis to forced climate simulations, such as those following the protocol of the project.
Computational approach
Technological challenges associated with my PhD work are those of data storage and accessibility to it. Since I have to work with rather large amounts of data, I will need a sufficiently extensive platform to store and manage them. Regarding accessibility, so far, I have used ESGF nodes to download the data I needed. However, since I want to apply my analyses to the outputs of as many climate models as possible, I do not rule out the possibility that, in the future, I might need an easier way to access them than the current method (i.e., manually downloading datasets one by one), as well as to serialize the operations to be performed on them.
Image
The image shown here illustrates the temporal evolution of some key SPG variables before a convection/surface cooling shutdown event in the Labrador Sea. So far, the sequence of events has been analyzed using a single model. My goal is to strengthen the proposed storyline by verifying the presence of similar mechanisms across as many models as possible, retaining that multimodel consistency is the first step towards the construction of physically plausible explanation of the processes.
Key results
Recent observations indicate two distinct drivers of interrupted winter convection in the Labrador Sea: anomalous atmospheric forcing and the advection of freshwater anomalies. We tested whether these mechanisms arise spontaneously under stationary pre-industrial climate conditions using six medium to high-resolution CMIP6 control simulations. We identified recurrent shutdowns of Subpolar Gyre deep convection driven primarily by persistent negative NAO phases, which suppress winter surface heat loss and inhibit convective preconditioning. In addition, rare but more persistent shutdowns occur when freshwater anomalies of Arctic origin reach the Labrador Sea, enhancing stratification and sea-ice formation. Our results demonstrate that both ob- served drivers of Labrador Sea convection interruption are intrinsic features of internal variability of state-of-the-art climate models, providing a baseline for assessing their amplification under anthropogenic warming.
Resource usage
XXXXXXXXXXXXXXXXXX
What's next
At the state of the art, the tipping of the Subpolar Gyre deep convection should be located in the larger framework of Atlantic Meridional Overturning Circulation (AMOC) potential collapse. Indeed, recent model based studies highlighted how various the stability landscape of AMOC can be, suggesting that a variety of intermediate tipping possibly getting the system closer to a full shutdown configuration could arise, including SPG deep convection interruption. From now to the end of my PhD the analysis of the dynamical features of metastable SPG configurations will be the main focus of my investigation.
Image
Standardized monthly evolution of (a) NAO index and downward surface heat flux (∆F); (b) surface density (∆ρ), and its thermal and haline components, starting two years before the events. Standardized March MLD anomalies are shown as orange squares. Shading and bars indicate intermodel spread (one standard deviation σ). Coral vertical shading highlights wintertime before shutdown events.
Marco Buccellato
CNR - ISAC; University of Bologna
My name is Marco Buccellato and I am a Physics of the Earth system master graduate at the university of Bologna. Along my education and my academic path I had the possibility to face a very wide spectrum of practices, each one requiring different skills. Starting from a classical studies background and environment, the bachelor and master degree in Physics and Physics of the Earth system provided me flexible and critical problem solving abilities and made me understand the importance of team work in addressing precise scientific questions. I always strongly believed that an integration of different typologies of expertise plays a crucial role in problem analysis. According to this, the way the climate question requires the complementary intervention of a deep knowledge of fundamentals of physics as well as of the ability to deal with political and socio-economic issues has been intriguing me since my first steps in the world of science.