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Tipping Points in the Earth System

Periodic Reporting for period 1 - TiPES (Tipping Points in the Earth System)

Reporting period: 2019-09-01 to 2021-02-28

Tipping points can best be described as critical thresholds where the climate system as a whole, or its components, referred to as tipping elements, transition from one stable state to another. This occurs by way of a drastic and irreversible change that catalyzes a domino effect of feedback mechanisms, resulting in a cascade of numerous dramatic changes.

The Earth has gone through abrupt transitions through its history, but the underlying mechanisms are still not fully understood, nor can current models simulate past abrupt transitions realistically. TiPES contributes to better prediction of possible future abrupt changes caused by anthropogenic global warming, clarify what crossing the tipping points means socioeconomically, and help policymakers plan strategies to create safe operating spaces for humanity.

There is rising concern that several subsystems of the Earth may respond highly nonlinearly at critical future levels of anthropogenic forcing; these levels have recently been associated with tipping points (TPs). It is paramount to identify safe operating spaces for humanity and the planet in terms of these critical forcing levels in order to prevent harmful transitions to alternative, undesirable states of the Earth system. The mechanisms leading to such abrupt transitions are only partly understood and state-of-art Earth System Models appear to respond too smoothly at TPs and have difficulties in simulating abrupt transitions that occurred in the planet’s history.

TiPES will address these problems from several angles:

1. The project will identify subsystems that may exhibit abrupt transitions, and couplings between them, by focusing on paleoclimatic records and abrupt transitions therein. Novel methods to detect Early Warning Signals of forthcoming TPs, and to make skillful predictions on their basis, will be developed.

2. The potential shortcomings of models in representing TPs will be evaluated; in particular, TiPES will investigate how Bayesian calibration techniques can help enable these models to simulate past abrupt transitions.

3. TiPES will develop a generalized theory of climate sensitivity that accounts for the presence of TPs and feedbacks across various time scales.

4. To define safe operating spaces. TiPES will focus on dynamical system theory and on global stability notions for non-autonomous systems in order to estimate the stability of desirable states.

5. The results obtained by the project will be communicated to policy makers in a manner that facilitates decisions and their implementation. TiPES will develop formal approaches to define the socioeconomic risks of crossing TPs, and to derive decision strategies to keep anthropogenic forcing below levels where abrupt transitions may occur.
The TiPES project have now been active for 18 months and we are progressing well within all work packages and tasks.
Despite the COVID pandemic we have remained very active and have a total of 54 open access publications acknowledging the project, of these two are in the high impact journal of PNAS and three are in SCIENCE. Another 46 are submitted or close to submission.

Out of the many published TiPES papers, we will in the following only highlight a few. More complete accounts are found in the 18 months reporting. Pinning down the sequences of events in past tipping points is a strong focus in TiPES (WP1). Svensson et al. (Clim. Past) have published a synchronization between volcanic eruptions found as tephra layers in Greenland and Antarctic ice cores. Since most tephra found in ice cores has a local origin, such as Icelandic eruptions seen in Greenland, the events that can be identified in both hemispheres are the ones with a global impact, from which a climatic response could be expected. Based on this a connection between volcanic eruptions and triggering of DO-events has now been established (Lohmann et al., submitted). Nehrbass-Ahles et al. (Science) have identified abrupt changes in atmospheric CO2 content in Antarctic ice-cores under both cold and warm conditions. This is an important finding, as CO2 is found to be not only a warming agent, but a controlling factor for climate stability (Vettoretti et al., submitted) (WP1+2). For assessing changes in extremes, statistics are a challenge, thus reliable estimates through time are important. Grindsted et al. (PNAS) used accounts of damages combined with area weighted development and population densities to find a significant increase in the extreme tail of the distribution of hurricanes making landfall at the American East coast. Methods for identifying early warning signals (EWS) for forthcoming tipping points have been developed (WP1-3) and indications of EWS are found for the Amazon rainforest (Ciemer et al. Environ. Res. Lett.) and for collapse of the Greenland ice sheet (Boers and Rypdal, PNAS). The ability of State-of-the-art climate models to capture abrupt changes and tipping points are investigated through model simulations (WP3). Meccia et al. (GRL) investigated the response in EC-Earth to external forcing if stochasticity is included in the parametrization (WP3-4). Here collapse of Arctic winter sea ice is observed. In a study using the HadGEM3-GC2 Jackson and Wood (J. Clim) investigated optimal fingerprints for collapse of the AMOC, which can potentially be used as EWS before any changes in AMOC can be monitored. The physics of climate variability has been described by Ghil and Lucarini (Rev Mod Phys.) in a comprehensive review. With the risk of tipping points, measures of climate sensitivity, which is inherently a linear concept, must be generalized (WP4). This was done by Ashwin and v d Heydt (J Stat Phys) to include the case of bifurcations, while Bodia et al. (Chaos) question the linear response regarding geoengineering. While in a series of papers advanced techniques such as Markov chains (Gutierrez and Lucarini, J Stat Phys), response operators (Lembo et al. Scientific reports) and unstable periodic orbits (Lucarini and Gritsun, Climate Dynamics). Finally has Kuehn and Soresina (SN Partial Differ. Equ. Appl.) progressed the mathematics involved with many temporal and spatial scales in the climate, by developing numerical continuation techniques for fast-reaction systems.
Expected results are:
1) A better understanding of abrupt climate change, of climate-related Earth system tipping elements and their tipping points, and associated impacts.
2) An identification of safe operating spaces, accompanied – where relevant – with long-term strategies for preventing or mitigating impacts.
3) An advance of the understanding of respective impacts and early warning indicators.

TiPES is only within the first 18 months and several of the impacts expected are anticipated later, when more results emerge.
However, TiPES have already by now been recognized for its work several places e.g. in November 2020 TiPES was highlighted as project of the month in the magazine Research*eu for “A new model to accurately predict severe drought in the amazon-18 months in advance!”(Union, 2020) as presented by Ciemer et al., 2020 (T#24, EU#23) and in February 2021 editors of the AGU journals highlighted the “New Technique to Estimate Climate Sensitivity,” presented by Bastiaansen et al., 2021 (T#43, EU#50) on “Multivariate estimations of equilibrium climate sensitivity from short transient warming simulations”. In addition several TiPES individuals have received recognitions.
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