Predictability of tipping points with rate-dependent effects

2021 ◽  
Author(s):  
Johannes Lohmann ◽  
Peter Ditlevsen
Keyword(s):  
Early Warning ◽  
Control Parameter ◽  
Initial Conditions ◽  
Ocean Model ◽  
Rate Of Change ◽  
Global Ocean ◽  
Critical Threshold ◽  
Tipping Points ◽  
Operating Space ◽  
Safe Operating

<p>Due to non-linearities in the dynamics of crucial elements in the climate system, Earth’s safe operating space is limited. Beyond a certain level of a control parameter, such as the atmospheric Greenhouse gas concentration, qualitative regime shifts in one or more sub-systems may take place. Additionally, theoretical studies suggest that abrupt, irreversible change can happen already prior to the crossing of a critical threshold in a control parameter.</p><p>In these so-called rate-induced transitions, the effective parameter level to induce tipping depends on the rate of change, or more generally the precise trajectory of the changing control parameter. Here we show rate-induced tipping points of the overturning circulation in a global ocean model. Due to the chaotic dynamics of the system, whether there will be tipping or not depends both on the rate and initial conditions in a very sensitive, non-smooth way. This raises questions about whether the safe operating space is still well-defined, and whether an approach of its boundary can be predicted.</p><p>For tipping points associated with slow passages across a bifurcation, generic early-warning signals have been developed for these purposes. Due to the necessarily fast parameter changes involved in rate-induced tipping, early-warning is more challenging. In many cases the tipping involves a saddle escape, which results in a delay of the actual transition and can be exploited for early-warning. Here this is demonstrated in the context of low-dimensional models. While due to the sensitivity of the dynamics around the saddle one might not be able to predict with certainty whether and when the system will tip, the indicators presented here may allow issuing a warning as the system gets close to tipping.</p>

scholarly journals Risk of tipping the overturning circulation due to increasing rates of ice melt

2021 ◽  
Vol 118 (9) ◽  
pp. e2017989118
Author(s):  
Johannes Lohmann ◽  
Peter D. Ditlevsen
Keyword(s):  
Complex Systems ◽  
Climate Model ◽  
Rate Of Change ◽  
Meridional Overturning Circulation ◽  
Climate System ◽  
Global Ocean ◽  
Tipping Points ◽  
Parameter Change ◽  
Overturning Circulation ◽  
Critical Thresholds

Central elements of the climate system are at risk for crossing critical thresholds (so-called tipping points) due to future greenhouse gas emissions, leading to an abrupt transition to a qualitatively different climate with potentially catastrophic consequences. Tipping points are often associated with bifurcations, where a previously stable system state loses stability when a system parameter is increased above a well-defined critical value. However, in some cases such transitions can occur even before a parameter threshold is crossed, given that the parameter change is fast enough. It is not known whether this is the case in high-dimensional, complex systems like a state-of-the-art climate model or the real climate system. Using a global ocean model subject to freshwater forcing, we show that a collapse of the Atlantic Meridional Overturning Circulation can indeed be induced even by small-amplitude changes in the forcing, if the rate of change is fast enough. Identifying the location of critical thresholds in climate subsystems by slowly changing system parameters has been a core focus in assessing risks of abrupt climate change. This study suggests that such thresholds might not be relevant in practice, if parameter changes are not slow. Furthermore, we show that due to the chaotic dynamics of complex systems there is no well-defined critical rate of parameter change, which severely limits the predictability of the qualitative long-term behavior. The results show that the safe operating space of elements of the Earth system with respect to future emissions might be smaller than previously thought.

scholarly journals The tipping points and early-warning indicators for Pine Island Glacier, West Antarctica

2020 ◽  
Author(s):  
Sebastian H. R. Rosier ◽  
Ronja Reese ◽  
Jonathan F. Donges ◽  
Jan De Rydt ◽  
G. Hilmar Gudmundsson ◽  
...  
Keyword(s):  
Mass Loss ◽  
Early Warning ◽  
Ice Sheet ◽  
Systematic Investigation ◽  
Critical Threshold ◽  
Tipping Points ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
Early Warning Indicators ◽  
Warning Indicators

Abstract. Mass loss from the Antarctic Ice Sheet is the main source of uncertainty in projections of future sea-level rise, with important implications for coastal regions worldwide. Central to this is the marine ice sheet instability: once a critical threshold, or tipping point, is crossed, ice-internal dynamics can drive a self-amplifying retreat committing a glacier to irreversible, rapid and substantial ice loss. This process might have already been triggered in the Amundsen Sea region, where Pine Island and Thwaites glaciers dominate the current mass loss from Antarctica, but modelling and observational techniques have not been able to establish this rigorously, leading to divergent views on the future mass loss of the WAIS. Here, we aim at closing this knowledge gap by conducting a systematic investigation of the stability regime of Pine Island Glacier. To this end we show that early warning indicators robustly detect critical slowing for the marine ice sheet instability. We are thereby able to identify three distinct tipping points in response to increases in ocean-induced melt. The third and final event, triggered by an ocean warming of approximately 1.2 °C from the steady state model configuration, leads to a retreat of the entire glacier that could initiate a collapse of the West Antarctic Ice Sheet.

Sensitivity of CFC-11 uptake to physical initial conditions and interannually varying surface forcing in a global ocean model

2009 ◽  
Vol 29 (1) ◽  
pp. 58-65 ◽  
Author(s):  
Gokhan Danabasoglu ◽  
Synte Peacock ◽  
Keith Lindsay ◽  
Daisuke Tsumune
Keyword(s):  
Initial Conditions ◽  
Ocean Model ◽  
Global Ocean

What is the evidence for planetary tipping points?

2017 ◽  
Author(s):  
Barry W. Brook ◽  
Erle C. Ellis ◽  
Jessie C. Buettel
Keyword(s):  
Regime Shift ◽  
Anthropogenic Impacts ◽  
Resource Extraction ◽  
State Transitions ◽  
Tipping Points ◽  
Theoretical Justification ◽  
Positive Feedbacks ◽  
Global Environmental ◽  
Operating Space ◽  
Safe Operating

This chapter critically evaluates the likelihood that planet Earth will cross one or more global environmental tipping points, resulting in a degraded state that would be difficult to reverse. Ecological tipping points occur when components of a system change rapidly due an initial forcing that is amplified by positive feedbacks, resulting in a regime shift. The chapter examines the evidence in support of biological and geophysical boundaries that clearly delimit a “safe operating space” for people and biodiversity. For individual ecosystems, abrupt state transitions have been documented. However, apart from the climate system, there is scant evidence (or theoretical justification) to support the view that global aggregates like biodiversity, chemical cycles, or resource extraction have planetary thresholds that define the boundaries of a global safe operating space. Acknowledging the absence of clear evidence for thresholds or boundaries at the global level does not diminish the seriousness of anthropogenic impacts. It does, however, imply that local-scale mitigation actions will be most effective.

scholarly journals On the Role of Westerly Wind Anomalies in the Development of the 1982–1983 El Niño

2021 ◽  
Author(s):  
David J. Webb
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Initial Conditions ◽  
El Nino ◽  
Ocean Model ◽  
Global Ocean ◽  
Westerly Wind ◽  
The North ◽  
North Equatorial Counter Current ◽  
Counter Current

Abstract. A recent study of two strong El Niños highlighted the potential importance of a region of low sea level that developed in the western equatorial Pacific prior to the El Niños of 1982–1983 and 1997–1998. Here the cause of the low sea level in 1982 is investigated using a series of runs of a global ocean model with different wind fields and initial conditions. The results indicate that the low sea level was due to the increased wind shear that developed just north of the Equator during 1982. This generated Ekman divergence at the latitudes of the North Equatorial Trough, raising the underlying density surfaces and increasing the depth of the trough. This also increased the strength of the North Equatorial Counter Current which lies on the southern slope of the trough. The anomalous westerly winds associated with Madden Julian Oscillations are often held responsible for triggering El Niños through the generation of westerly wind bursts and the resulting equatorial Kelvin waves in the ocean. However if Webb (2018) is correct, the present results imply that a different physical process was involved in which Ekman divergence due to the same winds, increased the heat transported by the North Equatorial Counter Current early in the year and ultimately caused the strong 1982–1983 El Niño.

A digital contract for restoration of the Earth System mediated by a Planetary Boundary Exchange Unit

2021 ◽  
pp. 205301962098727
Author(s):  
Orfeu Bertolami ◽  
Frederico Francisco
Keyword(s):  
Earth System ◽  
New Governance ◽  
Validation Process ◽  
Operational Conditions ◽  
Blockchain Technology ◽  
The Earth ◽  
Optimal Functioning ◽  
Operating Space ◽  
Exchange Unit ◽  
Safe Operating

In this paper, we propose a new governance paradigm for managing the Earth System based on a digital contract inspired on blockchain technology. This proposal allows for a radical decentralisation of the procedures of controlling, maintaining and restoring ecosystems by a set of networks willing to engage in improving the operational conditions of local ecosystems so to contribute to an optimal functioning of the Earth System. These procedures are aimed to improve local Planetary Boundary parameters so that they approach the optimal Holocene reference values, the so-called Safe Operating Space, via a reciprocal validation process and an exchange unit that internalises the state of the Earth System.

scholarly journals Ensemble forecasting greatly expands the prediction horizon for ocean mesoscale variability

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Prasad G. Thoppil ◽  
Sergey Frolov ◽  
Clark D. Rowley ◽  
Carolyn A. Reynolds ◽  
Gregg A. Jacobs ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Mesoscale Dynamics ◽  
Predictive Skill ◽  
Freshwater Transport ◽  
Prediction Horizon ◽  
Initial Location ◽  
Ocean Models ◽  
High Uncertainty

AbstractMesoscale eddies dominate energetics of the ocean, modify mass, heat and freshwater transport and primary production in the upper ocean. However, the forecast skill horizon for ocean mesoscales in current operational models is shorter than 10 days: eddy-resolving ocean models, with horizontal resolution finer than 10 km in mid-latitudes, represent mesoscale dynamics, but mesoscale initial conditions are hard to constrain with available observations. Here we analyze a suite of ocean model simulations at high (1/25°) and lower (1/12.5°) resolution and compare with an ensemble of lower-resolution simulations. We show that the ensemble forecast significantly extends the predictability of the ocean mesoscales to between 20 and 40 days. We find that the lack of predictive skill in data assimilative deterministic ocean models is due to high uncertainty in the initial location and forecast of mesoscale features. Ensemble simulations account for this uncertainty and filter-out unconstrained scales. We suggest that advancements in ensemble analysis and forecasting should complement the current focus on high-resolution modeling of the ocean.

scholarly journals Validation of an ocean shelf model for the prediction of mixed-layer properties in the Mediterranean Sea west of Sardinia

Ocean Science ◽  
2017 ◽  
Vol 13 (2) ◽  
pp. 235-257 ◽  
Author(s):  
Reiner Onken
Keyword(s):  
Boundary Conditions ◽  
Mixed Layer ◽  
Initial Conditions ◽  
Mixed Layer Depth ◽  
Vertical Mixing ◽  
Global Ocean ◽  
Wave Number ◽  
Surface Boundary ◽  
Regional Ocean Modeling System ◽  
The Mediterranean

Abstract. The Regional Ocean Modeling System (ROMS) has been employed to explore the sensitivity of the forecast skill of mixed-layer properties to initial conditions, boundary conditions, and vertical mixing parameterisations. The initial and lateral boundary conditions were provided by the Mediterranean Forecasting System (MFS) or by the MERCATOR global ocean circulation model via one-way nesting; the initial conditions were additionally updated through the assimilation of observations. Nowcasts and forecasts from the weather forecast models COSMO-ME and COSMO-IT, partly melded with observations, served as surface boundary conditions. The vertical mixing was parameterised by the GLS (generic length scale) scheme Umlauf and Burchard (2003) in four different set-ups. All ROMS forecasts were validated against the observations which were taken during the REP14-MED survey to the west of Sardinia. Nesting ROMS in MERCATOR and updating the initial conditions through data assimilation provided the best agreement of the predicted mixed-layer properties with the time series from a moored thermistor chain. Further improvement was obtained by the usage of COSMO-ME atmospheric forcing, which was melded with real observations, and by the application of the k-ω vertical mixing scheme with increased vertical eddy diffusivity. The predicted temporal variability of the mixed-layer temperature was reasonably well correlated with the observed variability, while the modelled variability of the mixed-layer depth exhibited only agreement with the observations near the diurnal frequency peak. For the forecasted horizontal variability, reasonable agreement was found with observations from a ScanFish section, but only for the mesoscale wave number band; the observed sub-mesoscale variability was not reproduced by ROMS.

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