Fairbrother Lecture 2024

Background info

The 2024 Fairbrother Lecture on "Uncertain currents - Predicting tipping points in our ocean and climate" took place on 30 April at the Reading Biscuit Factory. Here you can find background information, supporting references and a recording of the lecture.

For many of us the climate crisis mainly calls to mind rising global temperatures, but the crisis goes far beyond this – we are at risk of pushing our planet across climate ‘tipping points,’ critical thresholds where small changes can lead to abrupt and irreversible shifts in the Earth’s climate system.

One major element in climate tipping is a huge system of ocean currents, the Atlantic Meridional Overturning Circulation (AMOC), which is responsible for Europe's relatively mild climate. Past climate patterns show that these currents can switch abruptly between today’s vigorous flow and a much weaker flow state. A future shutdown would have potentially devastating consequences in Europe and around the world.

Media stories often paint a catastrophic picture of possible climate futures, with runaway ice sheet collapse, abrupt sea level rise and rainforest dieback, possibly triggered as early as this decade. But how close to these tipping points are we really?

Scientists work continuously to improve methods for predicting tipping points, meaning that our available knowledge shifts and develops. The complexity of the climate system also means significant uncertainties remain about tipping thresholds. Given this complexity and changing states of knowledge, how realistic is our yearning for fixed and definite answers and how should we best manage risk with limited knowledge?

In this lecture doctoral researcher in mathematics of climate, Reyk Börner, gives an inside view of what we know, don’t know, and perhaps can’t know about the future of our ocean currents and climate.

About the Fairbrother Lecture

The Fairbrother Lecture is a University public lecture organised by the Doctoral and Researcher College at University of Reading. It is named after Jack Fairbrother who in 1929 became one of the first students to be awarded a PhD from the University. The lecture is an annual event at which a Reading doctoral researcher presents their research to a wider audience. For further information and links to other lecture see here.

Watch the lecture

Supporting references

In the following, you'll find a selection of scientific publications and further links to the information sources and visuals used in the lecture, ordered chronologically by themes.

Time scales and irreversibility

The two quotes are paraphrases from the short film 'Coastal Requiem' by Diane Tuft that was screened before the lecture.

Climate tipping elements

For a scientific overview of climate tipping elements, including the examples discussed in the lecture, take a look at the references below. The recent Global Tipping Points Report also offers information on different levels of detail. The world map of climate tipping elements shown in the lecture is based on Armstrong McKay et al. (2022).

Lenton, T. M., Held, H., Kriegler, E., Hall, J. W., Lucht, W., Rahmstorf, S., & Schellnhuber, H. J. (2008). Tipping elements in the Earth’s climate system. Proceedings of the National Academy of Sciences, 105(6), 1786–1793. https://doi.org/10.1073/pnas.0705414105

Armstrong McKay, D. I., Staal, A., Abrams, J. F., Winkelmann, R., Sakschewski, B., Loriani, S., Fetzer, I., Cornell, S. E., Rockström, J., & Lenton, T. M. (2022). Exceeding 1.5°C global warming could trigger multiple climate tipping points. Science, 377(6611), eabn7950. https://doi.org/10.1126/science.abn7950

Alley, R. B., Marotzke, J., Nordhaus, W. D., Overpeck, J. T., Peteet, D. M., Pielke, R. A., Pierrehumbert, R. T., Rhines, P. B., Stocker, T. F., Talley, L. D., & Wallace, J. M. (2003). Abrupt Climate Change. Science, 299(5615), 2005–2010. https://doi.org/10.1126/science.1081056

Boers, N., Ghil, M., & Stocker, T. F. (2022). Theoretical and paleoclimatic evidence for abrupt transitions in the Earth system. Environmental Research Letters, 17(9), 093006. https://doi.org/10.1088/1748-9326/ac8944

Ashwin, P., Wieczorek, S., Vitolo, R., & Cox, P. (2012). Tipping points in open systems: Bifurcation, noise-induced and rate-dependent examples in the climate system. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 370(1962), 1166–1184. https://doi.org/10.1098/rsta.2011.0306

In the summary for policymakers of the IPCC Assessment Report 6, climate tipping elements are mentioned in section C.3, among other places. This article on CarbonBrief offers a nice overview of what the report says about tipping points.

Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S. L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., Gomis, M. I., Huang, M., Leitzell, K., Lonnoy, E., Matthews, J. B. R., Maycock, T. K., Waterfield, T., Yelekçi, Ö., Yu, R., & Zhou, B. (Eds.). (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. https://doi.org/10.1017/9781009157896

Positive feedbacks in the climate system

Polar ice sheets: Melt-elevation feedback

Robinson, A., Calov, R., & Ganopolski, A. (2012). Multistability and critical thresholds of the Greenland ice sheet. Nature Climate Change, 2(6), 429–432. https://doi.org/10.1038/nclimate1449

Other relevant positive feedbacks in ice sheets (not mentioned in the lecture) are the ice-albedo feedback and, particularly in Antarctica, the Marine Ice Sheet Instability (MISI).

Amazon rainforest: Forest-rain feedback

Staal, A., Tuinenburg, O. A., Bosmans, J. H. C., Holmgren, M., van Nes, E. H., Scheffer, M., Zemp, D. C., & Dekker, S. C. (2018). Forest-rainfall cascades buffer against drought across the Amazon. Nature Climate Change, 8(6), 539–543. https://doi.org/10.1038/s41558-018-0177-y

Zemp, D. C., Schleussner, C.-F., Barbosa, H. M. J., Hirota, M., Montade, V., Sampaio, G., Staal, A., Wang-Erlandsson, L., & Rammig, A. (2017). Self-amplified Amazon forest loss due to vegetation-atmosphere feedbacks. Nature Communications, 8(1), 14681. https://doi.org/10.1038/ncomms14681

Flores, B. M., Montoya, E., Sakschewski, B., Nascimento, N., Staal, A., Betts, R. A., Levis, C., Lapola, D. M., Esquível-Muelbert, A., Jakovac, C., Nobre, C. A., Oliveira, R. S., Borma, L. S., Nian, D., Boers, N., Hecht, S. B., ter Steege, H., Arieira, J., Lucas, I. L., … Hirota, M. (2024). Critical transitions in the Amazon forest system. Nature, 626(7999), 555–564. https://doi.org/10.1038/s41586-023-06970-0

Atlantic Meridional Overturning Circulation (AMOC)

Animation: 'Global Sea Surface Currents and Temperature', by Greg Shira, NASA/Goddard Space Flight Center Scientific Visualization Studio
Animation: 'The Thermohaline Circulation - The Great Ocean Conveyor Belt', by Greg Shira, NASA/Goddard Space Flight Center Scientific Visualization Studio. The Blue Marble Next Generation data is courtesy of Reto Stockli (NASA/GSFC) and NASA's Earth Observatory.
Movie reference: 'The Day After Tomorrow', dir. Roland Emmerich, 20th Century Fox (2004)

Here are some scientific papers discussing the multistability of the AMOC.

Weijer, W., Cheng, W., Drijfhout, S. S., Fedorov, A. V., Hu, A., Jackson, L. C., Liu, W., McDonagh, E. L., Mecking, J. V., & Zhang, J. (2019). Stability of the Atlantic Meridional Overturning Circulation: A Review and Synthesis. Journal of Geophysical Research: Oceans, 124(8), 5336–5375. https://doi.org/10.1029/2019JC015083

Kuhlbrodt, T., Griesel, A., Montoya, M., Levermann, A., Hofmann, M., & Rahmstorf, S. (2007). On the driving processes of the Atlantic meridional overturning circulation. Reviews of Geophysics, 45(2). https://doi.org/10.1029/2004RG000166

Marotzke, J., & Willebrand, J. (1991). Multiple Equilibria of the Global Thermohaline Circulation. Journal of Physical Oceanography, 21(9), 1372–1385. https://doi.org/10.1175/1520-0485(1991)021<1372:MEOTGT>2.0.CO;2

Lynch-Stieglitz, J. (2017). The Atlantic Meridional Overturning Circulation and Abrupt Climate Change. Annual Review of Marine Science, 9(Volume 9, 2017), 83–104. https://doi.org/10.1146/annurev-marine-010816-060415

Rahmstorf, S., Crucifix, M., Ganopolski, A., Goosse, H., Kamenkovich, I., Knutti, R., Lohmann, G., Marsh, R., Mysak, L. A., Wang, Z., & Weaver, A. J. (2005). Thermohaline circulation hysteresis: A model intercomparison. Geophysical Research Letters, 32(23). https://doi.org/10.1029/2005GL023655

Stommel model: Atlantic spherical cow

Stommel, H. (1961). Thermohaline Convection with Two Stable Regimes of Flow. Tellus, 13(2), 224–230. https://doi.org/10.1111/j.2153-3490.1961.tb00079.x

Past climate: ice core records

The ice core data are publicly available from the Centre for Ice and Climate at the Niels Bohr Institute, University of Copenhagen.

Dansgaard, W., Johnsen, S. J., Clausen, H. B., Dahl-Jensen, D., Gundestrup, N. S., Hammer, C. U., Hvidberg, C. S., Steffensen, J. P., Sveinbjörnsdottir, A. E., Jouzel, J., & Bond, G. (1993). Evidence for general instability of past climate from a 250-kyr ice-core record. Nature, 364(6434), 218–220. https://doi.org/10.1038/364218a0

Henry, L. G., McManus, J. F., Curry, W. B., Roberts, N. L., Piotrowski, A. M., & Keigwin, L. D. (2016). North Atlantic ocean circulation and abrupt climate change during the last glaciation. Science, 353(6298), 470–474. https://doi.org/10.1126/science.aaf5529

To construct the Arctic temperature timeseries over the past 100 thousand years shown in the lecture, I used datasets described in the following papers:

Kindler, P., Guillevic, M., Baumgartner, M., Schwander, J., Landais, A., & Leuenberger, M. (2014). Temperature reconstruction from 10 to 120 kyr b2k from the NGRIP ice core. Climate of the Past, 10(2), 887–902. https://doi.org/10.5194/cp-10-887-2014

Kaufman, D., McKay, N., Routson, C., Erb, M., Dätwyler, C., Sommer, P. S., Heiri, O., & Davis, B. (2020). Holocene global mean surface temperature, a multi-method reconstruction approach. Scientific Data, 7(1), 201. https://doi.org/10.1038/s41597-020-0530-7

Rantanen, M., Karpechko, A. Y., Lipponen, A., Nordling, K., Hyvärinen, O., Ruosteenoja, K., Vihma, T., & Laaksonen, A. (2022). The Arctic has warmed nearly four times faster than the globe since 1979. Communications Earth & Environment, 3(1), 1–10. https://doi.org/10.1038/s43247-022-00498-3

Future climate: Earth system models

Video: Comparison of cloud patterns observed with satellites vs. simulated by a climate model.

Projected AMOC strength until 2100

The figure source on the slide entitled "Projected AMOC strength until 2100" was falsely cited as originating from the IPCC Assessment Report 6. Instead, the figure is adapted from Fig. 6.8 of the Special Report on the Ocean and Cryosphere in a Changing Climate (2019).

IPCC, 2019: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, 755 pp. https://doi.org/10.1017/9781009157964

AMOC impacts

Papers cited in the lecture:

Liu, W., Xie, S.-P., Liu, Z., & Zhu, J. (2017). Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate. Science Advances, 3(1), e1601666. https://doi.org/10.1126/sciadv.1601666

Ritchie, P. D. L., Smith, G. S., Davis, K. J., Fezzi, C., Halleck-Vega, S., Harper, A. B., Boulton, C. A., Binner, A. R., Day, B. H., Gallego-Sala, A. V., Mecking, J. V., Sitch, S. A., Lenton, T. M., & Bateman, I. J. (2020). Shifts in national land use and food production in Great Britain after a climate tipping point. Nature Food, 1(1), 76–83. https://doi.org/10.1038/s43016-019-0011-3

Further articles on impacts of a potential future AMOC decline:

Liu, W., Fedorov, A. V., Xie, S.-P., & Hu, S. (2020). Climate impacts of a weakened Atlantic Meridional Overturning Circulation in a warming climate. Science Advances, 6(26), eaaz4876. https://doi.org/10.1126/sciadv.aaz4876

Van Westen, R. M., Kliphuis, M., & Dijkstra, H. A. (2024). Physics-based early warning signal shows that AMOC is on tipping course. Science Advances, 10(6), eadk1189. https://doi.org/10.1126/sciadv.adk1189

Bellomo, K., Meccia, V. L., D’Agostino, R., Fabiano, F., Larson, S. M., von Hardenberg, J., & Corti, S. (2023). Impacts of a weakened AMOC on precipitation over the Euro-Atlantic region in the EC-Earth3 climate model. Climate Dynamics, 61(7), 3397–3416. https://doi.org/10.1007/s00382-023-06754-2

Bellomo, K., Angeloni, M., Corti, S., & von Hardenberg, J. (2021). Future climate change shaped by inter-model differences in Atlantic meridional overturning circulation response. Nature Communications, 12(1), Article 1. https://doi.org/10.1038/s41467-021-24015-w

Predicting AMOC tipping points

The journal article about early-warning signs of an AMOC collapse and its media echo discussed in the lecture is by Ditlevsen & Ditlevsen (2023):

Ditlevsen, P., & Ditlevsen, S. (2023). Warning of a forthcoming collapse of the Atlantic meridional overturning circulation. Nature Communications, 14(1), Article 1. https://doi.org/10.1038/s41467-023-39810-w

Below are additional recent studies that look for early-warning signs of an AMOC tipping point.

Boers, N. (2021). Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation. Nature Climate Change, 11(8), 680–688. https://doi.org/10.1038/s41558-021-01097-4

Michel, S. L. L., Swingedouw, D., Ortega, P., Gastineau, G., Mignot, J., McCarthy, G., & Khodri, M. (2022). Early warning signal for a tipping point suggested by a millennial Atlantic Multidecadal Variability reconstruction. Nature Communications, 13(1), Article 1. https://doi.org/10.1038/s41467-022-32704-3

Uncertainty and limitations

These papers highlight some of the limitations and complexities of the climate system that make predictions of the future of the AMOC challenging and uncertain.

Mehling, O., Börner, R., & Lucarini, V. (2024). Limits to predictability of the asymptotic state of the Atlantic Meridional Overturning Circulation in a conceptual climate model. Physica D: Nonlinear Phenomena, 459, 134043. https://doi.org/10.1016/j.physd.2023.134043

Lohmann, J., Dijkstra, H. A., Jochum, M., Lucarini, V., & Ditlevsen, P. D. (2024). Multistability and intermediate tipping of the Atlantic Ocean circulation. Science Advances, 10(12), eadi4253. https://doi.org/10.1126/sciadv.adi4253

Ben-Yami, M., Morr, A., Bathiany, S., & Boers, N. (2023). Uncertainties too large to predict tipping times of major Earth system components. arXiv Preprint arXiv:2309.08521.

Ditlevsen, P. D., & Johnsen, S. J. (2010). Tipping points: Early warning and wishful thinking. Geophysical Research Letters, 37(19).

Romanou, A., Rind, D., Jonas, J., Miller, R., Kelley, M., Russell, G., Orbe, C., Nazarenko, L., Latto, R., & Schmidt, G. A. (2023). Stochastic Bifurcation of the North Atlantic Circulation under a Midrange Future Climate Scenario with the NASA-GISS ModelE. Journal of Climate, 36(18), 6141–6161. https://doi.org/10.1175/JCLI-D-22-0536.1

Knutti, R., & Stocker, T. F. (2002). Limited Predictability of the Future Thermohaline Circulation Close to an Instability Threshold. Journal of Climate, 15(2), 179–186. https://doi.org/10.1175/1520-0442(2002)015<0179:LPOTFT>2.0.CO;2

Outlook

The figure on the slide "No tipping ahead - all linear?" is Fig. SPM.10 in the Summary for Policymakers of the IPCC Assessment Report 6 (2021).

The metaphor of a house fire to illustrate risk management under uncertainty was inspired by a talk by Richard Wood (UK Met Office).

Thank you for your interest in the lecture! To learn more about my own research, visit my personal website.