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Jonathan Rosser @jonathanrosser.bsky.social · 29/04/2026

The AMOC: what is it, how is it changing and why does it matter? Been hearing a lot about the AMOC and want to know more about what it is and why it matters? My colleagues (Ruth Chapman and Georgina Kyriacou) and I at the @granthamlse.bsky.social have written an explainer on the AMOC.

lse.ac.uk

The AMOC: what is it, how is it changing and why does it matter? - Grantham Research Institute on climate change and the environment

What is the AMOC? AMOC stands for ‘Atlantic Meridional Overturning Circulation’. This is a giant conveyor belt moving warm, salty...

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Jonathan Rosser @jonathanrosser.bsky.social · 23/03/2026

Please do get in touch if you would like to hear more, collaborate, or if you have any comments or suggestions. Photo Credit to Gaia Scianca

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Jonathan Rosser @jonathanrosser.bsky.social · 23/03/2026

We have ongoing work in ensemble design, socio-economic impacts of AMOC change, and potential future work on uncertainties around the North Atlantic Subpolar Gyre.

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Jonathan Rosser @jonathanrosser.bsky.social · 23/03/2026

I also flagged our intention to organise further discussions and workshops around climate ensemble design, climate economics, and how to better align climate science with information provision for decision-makers.

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Jonathan Rosser @jonathanrosser.bsky.social · 23/03/2026

They have covered a range of current work from workshops on how to use climate information for policy makers and the financial institutions, the design of climate model ensembles, and our assessments of uncertainties around the impacts of the Atlantic Meridional Overturning Circulation.

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Jonathan Rosser @jonathanrosser.bsky.social · 23/03/2026

***Seminars on Climate Uncertainty, Decision-making, and AMOC changes*** I have really enjoyed giving seminars at Uppsala University, Stockholm University, SMHI, and Lund University over the past few weeks.

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Jonathan Rosser @jonathanrosser.bsky.social · 19/02/2026

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

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Reposted by Jonathan Rosser

Zack Labe @zacklabe.com · 18/02/2026

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...) 🌊

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 18/02/2026

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 18/02/2026

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 17/02/2026

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!

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Jonathan Rosser @jonathanrosser.bsky.social · 17/02/2026

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 17/02/2026

*** 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...

osm26.ipostersessions.com

AGU - iPosterSessions - an aMuze! Interactive system

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

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".

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

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

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

▪️ 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

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Jonathan Rosser @jonathanrosser.bsky.social · 10/09/2025

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

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Reposted by Jonathan Rosser

ClimTip | Climate Tipping Points in the Earth System @climtip.bsky.social · 19/08/2025

🌊 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...

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Jonathan Rosser @jonathanrosser.bsky.social · 18/08/2025

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...

economist.com

The shutdown of ocean currents could freeze Europe

When climate change poses a strategic threat, it needs a strategic response

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Jonathan Rosser @jonathanrosser.bsky.social · 15/08/2025

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/...

economist.com

Earth’s climate is approaching irreversible tipping points

Scientists are racing to work out just how close they might be

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Jonathan Rosser @jonathanrosser.bsky.social · 28/07/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 28/07/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 28/07/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 28/07/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 28/07/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 28/07/2025

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:

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Jonathan Rosser @jonathanrosser.bsky.social · 28/07/2025

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).

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Jonathan Rosser @jonathanrosser.bsky.social · 22/07/2025

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 .

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Jonathan Rosser @jonathanrosser.bsky.social · 22/07/2025

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.

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Jonathan Rosser @jonathanrosser.bsky.social · 22/07/2025

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

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Jonathan Rosser @jonathanrosser.bsky.social · 22/07/2025

The three key takeaways are as follows: 1) We describe long-term convective oscillations seen in the Southern Ocean of the majority of the CMIP6 (global climate) models that we analysed.

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Jonathan Rosser @jonathanrosser.bsky.social · 22/07/2025

I am excited to announce our new preprint "Shutdown of Southern Ocean Convective Centennial Variability under Global Warming and Implications for Climate Projections". This is the first paper on content from my PhD thesis and I am so happy that it is now submitted. essopenarchive.org/users/946271...

essopenarchive.org

Shutdown of Southern Ocean Convective Centennial Variability under Global Warming and Implications for Climate Projections

Centennial oscillations occur in the Southern Ocean in the majority of an ensemble of pre-industrial control runs of 16 CMIP6 models. These oscillations involve features such as the Antarctic Circumpo...

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Jonathan Rosser @jonathanrosser.bsky.social · 11/07/2025

Full-time | Fixed until 29 September 2027 | London-based | Hybrid Working Salary: £42,679 to £51,000 (up to £54,730 with progression) Deadline: Sunday 24 August 2025 (23.59 UK time) To apply or for more information: jobs.lse.ac.uk/Vacancies/W/...

jobs.lse.ac.uk

Research Officer (RobustAssess)

Research Officer (RobustAssess), , LSE is committed to building a diverse, equitable and truly inclusive university <p style="text-align: cente...

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Jonathan Rosser @jonathanrosser.bsky.social · 11/07/2025

You will: Use low-dimensional non-linear models to understand model error and uncertainty in climate models. Design a system for ensemble design to understand the full range of climate responses. Collaborate with us to assess the economic impacts of tipping points and understand their uncertainty.

lnkd.in

This link will take you to a page that’s not on LinkedIn

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Jonathan Rosser @jonathanrosser.bsky.social · 11/07/2025

Focus: The post-holder will work with Professor David Stainforth and myself on the utility of climate model simulations for understanding climate tipping points such as the Atlantic Meridional Overturning Circulation (AMOC) and the Sub-Polar Gyre (SPG).

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Jonathan Rosser @jonathanrosser.bsky.social · 11/07/2025

We're hiring! Research Officer on the RobustAssess project, funded by @aria-research.bsky.social . Join the @granthamlse.bsky.social and the London School of Economics as a Research Officer and work on climate tipping points and the future of climate model ensembles.

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Jonathan Rosser @jonathanrosser.bsky.social · 09/07/2025

Fantastic work from the UK OBR and CCC, presented by Carbon Brief, showing how the estimated costs of climate change for the UK have increased from around 5% to 8% of GDP by 2070 under 3C of warming, while the cost of avoiding is much lower and has roughly halved since the last estimate!

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Jonathan Rosser @jonathanrosser.bsky.social · 02/07/2025

I also spoke about our upcoming work on expert elicitations on the AMOC and economic impacts, decision-making under the deep uncertainty, and how to produce climate information to aid these decisions. Please do get in touch if you have any questions, or would like to collaborate/ discuss further!

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Jonathan Rosser @jonathanrosser.bsky.social · 02/07/2025

I spoke about the significant uncertainties in our projections of when/ if the Atlantic Overturning Circulation (AMOC) might collapse, the physical impacts this might have, and how this might impact our societies and economies.

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Jonathan Rosser @jonathanrosser.bsky.social · 02/07/2025

Had some fantastic conversations following my talk on "Economic impacts of AMOC tipping and uncertainty" at the Global Tipping Points Conference at University of Exeter.

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Jonathan Rosser @jonathanrosser.bsky.social · 10/06/2025

The engagement was fantastic and we had a really insightful discussion about climate governance, information, and communication.

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Jonathan Rosser @jonathanrosser.bsky.social · 10/06/2025

Thank you so much to @bas.ac.uk and @cambridgemba.bsky.social for inviting me to speak to their Executive MBA group about the economic impacts of climate change and the use of climate information in decision-making.

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Reposted by Jonathan Rosser

Kevin Pluck @kevpluck.bsky.social · 03/06/2025

Lowest global sea ice area for the date on record 🧪

Global sea ice area chart with a yellow arrow pointing at 2/6/2025 showing 17.52 million km²

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Jonathan Rosser @jonathanrosser.bsky.social · 01/05/2025

Really looking forward to presenting my work on the Economic consequences of CMIP Diversity and Targets for CMIP7 at #EGU25, do drop by if you would like to learn more about climate model uncertainty and its relevance for economic modelling.

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