Jonathan Rosser

I will, feel free to grab me at my poster session or drop me a dm/ email and we can find an alternative time.

Global map showing sea surface temperature anomalies in January 2026 relative to 1982 to 2010. Most areas are warmer than average. Red is shown for warmer sea surface temperatures, and blue is shown for colder sea surface temperatures. Data is from NOAA OISSTv2.1.

While the La Niña signature (cooling in the eastern Tropical Pacific) remained prevalent in January, there are signs it is beginning to fade in recent weeks. Elsewhere, anomalous warmth continues in the extratropics of both hemispheres.

Data from NOAA OISSTv2.1 (www.ncei.noaa.gov/products/opt...) 🌊

The RMT is the regional mean temperature of Northern Europe, using IPCC AR6 boundaries. We have conducted equivalent analysis for all of the IPCC AR6 boundaries and national boundaries, but focused on Northern Europe here as a relevant case study.

Thank you for your message, I'd be happy to discuss our work further if you would like to call sometime. The colours in Figure 3 represent the density of trajectories or how many runs enter a given part of the distribution, due to the methodology they don't correspond to probabilities.

I am also very interested in the economic impacts of these climate changes, and how we think about model information in this space more generally. I will be at my poster 4-6pm on Tue Feb 24th in the PS24A Session. Message to find out more or to meet up. I have attached a preview of the poster here!

If you would like to learn more about the uncertainty surrounding the impacts of changes to the Atlantic Meridional Overturning Circulation and approaches to projecting these impacts combined with global warming scenarios, please do come and chat.

*** Ocean Sciences Poster on "Uncertainty Quantification of the Regional Temperature Consequences of a Large AMOC Reduction"***
I will be presenting a poster at the Ocean Sciences Meeting #OSM next week. See this link for a sneak preview:
osm26.ipostersessions.com?s=77-E2-6D-B...

This means that we may be able to say more about the future of the Southern Ocean than we might expect from "initial condition anomalies".

Therefore, when we look at the change from "present day" (the initial value anomaly), the high initial condition uncertainty is spuriously moved to our projections, when we actually know our current conditions well, and the projections agree on our future trajectories.

This means that variance in the raw data is much higher at the start than the end of the run, due to initial condition impacts.

This is key for all modellers projecting the Southern Ocean (and potentially more widely). As shown in the attached figure, the Antarctic Circumpolar Current shows great variability in the present day but much lower in the future as long-timescale variability shuts down.

I am very excited about this point: it makes a huge difference whether we analyse raw data, changes from the "present day", or from "pre-industrial" in our models. Changes from the "present day" can mean projecting forward current variability and add potentially spurious uncertainty to projections.

▪️ Consequences for Climate Projections: Long timescale variability can contribute the majority of uncertainty in climate projections.

▪️ Shutdown of the lower circulation cell: Under even weak future forcing the oscillations are damped out and the strength of the lower circulation cell decreases

The key points were:
▪️ Centennial Oscillations: Southern Ocean oscillations on hundred-year timescales exist in the CMIP6 ensemble of global climate models

*** Presentation on Uncertainties in Climate Models and the Southern Ocean ***
Really enjoyed presenting at the Challenger Society Ocean Modelling Special Interest Group this week. For more info see our recent preprint: essopenarchive.org/users/946271...

🌊 The Atlantic “conveyor belt” (AMOC) is weakening under climate change. A new @nature.com study suggests collapse is unlikely this century, but the risks remain very serious.

Hear from lead author @jonbakerocean.bsky.social in our next webinar.

📅 2 Sep 2025, 2–3PM CEST
🔗 bit.ly/climtip-webi...

The shutdown of ocean currents could freeze Europe When climate change poses a strategic threat, it needs a strategic response

Great article in The Economist on the Atlantic Meridional Overturning Circulation (AMOC) and the impact of potential changes in it (a key focus of my current work). www.economist.com/leaders/2025...

Earth’s climate is approaching irreversible tipping points Scientists are racing to work out just how close they might be

It is good to see @economist.com highlighting the importance of climate tipping points, and the work being done to understand and prepare for them. It discusses the work being done by UK groups (including the @aria-research.bsky.social project which I am part of) www.economist.com/interactive/...

Finally, the thesis also shows that under global cooling (perhaps due to a future overshoot in temperatures), the Southern Ocean becomes destabilised, triggering new and faster oscillations (such as in the Antarctic Circumpolar Current), and even a counterintuitive loss of sea ice in some sectors.

^^For more on this point, see our recent preprint: essopenarchive.org/users/946271...

As centennial variability dominates the uncertainty in some of the Southern Ocean, this shutdown in variability dominates the behaviour of uncertainty in features (e.g. the Antarctic Circumpolar Current), so the initial oscillation state accounts for a large amount of uncertainty in trajectories.

Applying global warming forcing to the system leads to the shutdown of convection and the loss of the oscillatory behaviour (shown in figure). Under plausible future scenarios (SSP scenarios for CMIP), this shutdown occurs even with strong mitigation, suggesting a tipping point may have been passed.

These oscillations involve multiple mechanisms, both the more traditional heat release behaviour and a novel advective mechanism involving the gyres. While both mechanisms involve deep convection, the advective mechanism involves motion of heat around the gyre.

Centennial (roughly hundred year period) oscillations exist in the Southern Ocean across the CMIP6 ensemble of climate models. These oscillations can be seen in many features such as the ocean heat, currents (such as the Antarctic Circumpolar Current, shown in the figure), and dense water formation.

Thesis link: www.repository.cam.ac.uk/items/f8e627...
I will try to outline some of the key takeaways from my thesis in the rest of this post:

PhD Graduation!!
Very happy to finally graduate from my PhD, focusing on Southern Ocean Centennial Oscillations in the CMIP6 Ensemble”. I am incredibly grateful to all those who have supported me throughout, friends, family and colleagues (too many to name here,please check out my acknowledgements).

Many thanks to my co-authors Andrew Meijers, Peter Haynes, and Mark Webb.
Additional thanks to the institutions that have funded and/or supported my PhD and this research: @granthamlse.bsky.social, @climtip.bsky.social, C-CLEAR DTP, @bas.ac.uk, @metoffice.gov.uk .

3) The loss of this variability dominates our ability to make future projections about features in the Southern Ocean, such as the Antarctic Circumpolar Current and ocean heat uptake.

2) We also demonstrate that these oscillations and the associated dense water formation cease under all future climate scenarios.