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Tipping Points in the Earth System

Periodic Reporting for period 2 - TiPES (Tipping Points in the Earth System)

Reporting period: 2021-03-01 to 2022-08-31

The TiPES project has provided information and insight about tipping points in the Earth's system.
The project has advanced the theory and mathematics of tipping points, developed new methods to analyse and understand past climates, improved the understanding of climate tipping in large, state-of-the-art climate models and past climates, improved early warning methodology, and discovered that, indeed, the Amazon Rainforest, the West-central Greenland ice sheet, and the Atlantic Meridional Overturning Circulation all currently show signs of approaching tipping points.

Risk of tipping
Earth's history as well as climate theory indicate that different parts of the Earth system may be at risk of tipping with rising levels of atmospheric CO2 concentrations:
Climate data from the past document events where global temperatures shifted abruptly, indicating tipping points were passed.
Climate model simulations have revealed how accelerating amounts of atmospheric CO2 might tip different parts of the climate system causing changes in precipitation patterns, wind systems, temperature zones and ocean currents on timescales from years to decades.
Ecological, economical, and political impacts from such abrupt climate transitions are significant. Endemic biospheres such as the Amazon rainforest may be severely damaged. Committing to the loss of the Ice sheets of Greenland and West Antarctica over hundreds of years or the redistribution of heat in the North Atlantic Ocean over decades will shift sea levels, global weather patterns and monsoon patterns over the coming centuries. Consequently, climate tipping will pose significant challenges to natural ecosystems, agriculture, and infrastructure, as well as living conditions for humans in general.

Relevant focus points in the science of climate tipping
The risk of abrupt climate transitions calls for concise assessment and prediction of climate tipping points and development of early warning systems and mitigation strategies. Climate science, however, is currently not well prepared for such a scenario. The theory of abrupt climate transition is still in its infancy. The understanding of abrupt transitions in past climates is incomplete. Improvements are urgently needed in the identification of early warning signals and their subsequent implementation to predict the actual risk of tipping important climate subsystems such as the polar ice sheets, the tropical monsoon systems, and boreal forests. To facilitate an increased focus on tipping points political, economic and scientific stakeholders such as the IPCC and the climate science community must be engaged.
There has been a growing theoretical understanding of climate tipping during the project;

- Earth system models can now accurately simulate some past climate tipping events. This is an important progress, because such climate models generally depict climate change as smooth. However, in several TiPES-studies (Vettoretti et al. 2022 on CO2-window; Diamond et al. 2021 on Eemian sea ice puddles; Hopcroft and Valdes 2022 on the collapse of the Green Sahara) progress has been made
- The general understanding of climate tipping has been expanded during the TiPES project. The concept of partial climate tipping has been introduced and studied (Baastiansen et al. 2022; Lohmann et al. 2021). Additionally, rate-induced tipping, where the sheer speed of change to a system makes it tip, and noise-induced tipping, where the random disturbance of a system forces it to tip, have been explored. (ie. Boettner and Boers 2022, Ditlevsen 2022)
- the Earth system evolves dynamically and chaotically (Imagine a ball rolling down a mountain side during an earthquake). Insight into the delicate interplay of dynamical systems theory and chaos theory is advanced. The interplay and coupling of dynamical and chaotic systems and the relation to abrupt climate change is a priority in TiPES. (Lux et al. 2022, Vannitsem et al, 2021, Feliks, Y., J. Small and M. Ghil, 2021, Hummel, F., & Kuehn, C. (2022)
- TiPES has improved the methodology for equilibrium climate sensitivity, a key concept in climate science. Challenges regarding the relation between climate tipping and equilibrium climate sensitivity have been uncovered. (Bastiaansen, von der Heydt and Dikstra 2022; Bastiaansen, Ashwin, and von der Heydt, submitted)
-The study of abrupt transitions in past climates is crucial for understanding the risk of tipping events in the future (Boers, Ghil, and Stocker, 2022). It is challenged by the lack of homogeneity in paleo-data sources. To this end TiPES has contributed an automated analysis tool for identifying abrupt climate transitions across a diverse range of paleo-data and launched a database of high-quality paleo-data (PaleoJump, Bagniewski, Ghil and Rousseau (2021); moreover, a statistical framework to handle the dating uncertainties of paleoclimate records is also developed (Riechers and Boers, 2021; Myrvoll-Nilsen et al., 2022). Additionally, theoretical and experimental work has expanded the understanding of tipping events in the last 66 million years (Westerhold et al. 2020, Schmidely et al. 2021).

Within TiPES, the theory of precursor (early warning) signals for abrupt transitions is improved. Additionally, a method to exploit measurement series of ocean surface temperatures to assess the risk of tipping in the AMOC (ocean current system in the North Atlantic Ocean) has been developed (Boers, 2021; Lux et al, 2022; Jackson and Wood, 2020).
Early warning signals of tipping have been identified in the following climate sub-systems: The West-Central Greenland ice sheet has lost stability during the last century (Boers and Rypdal, 2021). A large part of the Greenland ice sheet situated in the central-western part of Greenland shows signs of so-called critical slowing down, indicating the system be nearing a point of no return, after which the ice could be committed – at least regionally - to an irreversible loss over the coming centuries. The AMOC shows signs of approaching a tipping point. This could happen within decades or in centuries, depending on the future anthropogenic global warming (Boers 2021, Michel et al. 2022). The Amazon rainforest has been losing resilience since the early 2000s, especially in parts closer to human activity (Boulton, Lenton, and Boers, 2022). The rainforest is in danger of shifting abruptly to a more savanna-like state within decades.
As outlined above, TiPES has contributed to the scientific understanding of tipping points and substantially advanced it beyond the state-of-the-art. We are disseminating our work to ensure the wider societal impact by the engagement of political and economical shareholders and the climate science community.

Our work has prompted the IPCC for a special report on “Climate Tipping Points and their Implications for Habitability and Resources”, which due to our work now have official status at the Swiss ministerial level. Outreach to politicians at the Danish Folkemøde for politicians and the general public has been performed. The joined TiPES, Comfort, TiPACCS Policy brief was well received at CINEA level. A list of research priorities and a call for a focused attention on abrupt climate transitions in the field of climate science was published in Environmental Research Letters. (N. Boers, M. Ghil, T. Stocker 2022) and meetings with several stakeholders, primarily within farming and insurance have been undertaken.