Seminar Archive – Summer 2025

Detecting abrupt changes in CMIP6 models

The CMIP6 data set may contain Strong Nonlinear Surprise (SNS) events in future climate-change projections. We build an automated detection algorithm that reproducibly selects the most extreme events in regions of at least one million square kilometer. We focus on two type of SNS events: abrupt changes (in the order of decades) and state transitions (often more than a century). Applying the tool to the ocean, sea-ice, and atmospheric variables of 54 models we isolate 73 SNS events, which we group into 4 abrupt change and 7 state transition categories. Of the identified SNSs 45% relates to sea-ice cover, 29% to mixed layer depth, 19% to ocean currents, and 7% to atmospheric systems like the Intertropical Convergence Zone. Between 0-2 °C global warming level we see an accelerated increase in the frequency of SNS after which the frequency levels off. In this talk we will highlight the design and rationale of the tool used to isolate these events.

Conditions for Instability in the Coupled Climate-Carbon System.

The CMIP6 project revealed that some of the latest generation of climate models show a very strong response to increased concentrations of atmospheric CO2, as quantified by equilibrium climate sensitivity (ECS). A high ECS could lead to a tipping point in the terrestrial carbon cycle, where rising global temperatures lead to increased carbon emissions from land, potentially leading to a self-reinforcing, ‘runaway’ climate state. In this talk, I will explore this risk using a combination of conceptual modelling and the complex land surface model JULES to identify the critical thresholds required to trigger such a tipping point.

Positive tipping points for nature.

The talk will identify positive tipping points for nature, highlighting how triggering them can help achieve the radical acceleration of change needed to reach widely agreed nature positive goals for 2030 and beyond. It will span positive ecological tipping points, positive social-ecological tipping points, and social tipping points that generate nature positive change, spread nature positive activities, and reduce key drivers of nature loss. Drawing together these tipping mechanisms I will highlight the potential to positively tip recovery of nature at larger scales and suggest how facilitating collective learning, properly valuing nature, and positively tipping worldviews to ecocentrism could further enable positive tipping points for nature.

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