32 research outputs found
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Interacting tipping elements increase risk of climate domino effects under global warming
With progressing global warming, there is an increased risk that one or several tipping elements in the climate system might cross a critical threshold, resulting in severe consequences for the global climate, ecosystems and human societies. While the underlying processes are fairly well-understood, it is unclear how their interactions might impact the overall stability of the Earth's climate system. As of yet, this cannot be fully analysed with state-of-the-art Earth system models due to computational constraints as well as some missing and uncertain process representations of certain tipping elements. Here, we explicitly study the effects of known physical interactions among the Greenland and West Antarctic ice sheets, the Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest using a conceptual network approach. We analyse the risk of domino effects being triggered by each of the individual tipping elements under global warming in equilibrium experiments. In these experiments, we propagate the uncertainties in critical temperature thresholds, interaction strengths and interaction structure via large ensembles of simulations in a Monte Carlo approach. Overall, we find that the interactions tend to destabilise the network of tipping elements. Furthermore, our analysis reveals the qualitative role of each of the four tipping elements within the network, showing that the polar ice sheets on Greenland and West Antarctica are oftentimes the initiators of tipping cascades, while the AMOC acts as a mediator transmitting cascades. This indicates that the ice sheets, which are already at risk of transgressing their temperature thresholds within the Paris range of 1.5 to 2 ∘C, are of particular importance for the stability of the climate system as a whole
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Network motifs shape distinct functioning of Earth’s moisture recycling hubs
Earth’s hydrological cycle critically depends on the atmospheric moisture flows connecting evaporation to precipitation. Here we convert a decade of reanalysis-based moisture simulations into a high-resolution global directed network of spatial moisture provisions. We reveal global and local network structures that offer a new view of the global hydrological cycle. We identify four terrestrial moisture recycling hubs: the Amazon Basin, the Congo Rainforest, South Asia and the Indonesian Archipelago. Network motifs reveal contrasting functioning of these regions, where the Amazon strongly relies on directed connections (feed-forward loops) for moisture redistribution and the other hubs on reciprocal moisture connections (zero loops and neighboring loops). We conclude that Earth’s moisture recycling hubs are characterized by specific topologies shaping heterogeneous effects of land-use changes and climatic warming on precipitation patterns
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Global warming due to loss of large ice masses and Arctic summer sea ice
Several large-scale cryosphere elements such as the Arctic summer sea ice, the mountain glaciers, the Greenland and West Antarctic Ice Sheet have changed substantially during the last century due to anthropogenic global warming. However, the impacts of their possible future disintegration on global mean temperature (GMT) and climate feedbacks have not yet been comprehensively evaluated. Here, we quantify this response using an Earth system model of intermediate complexity. Overall, we find a median additional global warming of 0.43 °C (interquartile range: 0.39−0.46 °C) at a CO2 concentration of 400 ppm. Most of this response (55%) is caused by albedo changes, but lapse rate together with water vapour (30%) and cloud feedbacks (15%) also contribute significantly. While a decay of the ice sheets would occur on centennial to millennial time scales, the Arctic might become ice-free during summer within the 21st century. Our findings imply an additional increase of the GMT on intermediate to long time scales
Complex networks of interacting stochastic tipping elements: cooperativity of phase separation in the large-system limit
Tipping elements in the Earth System receive increased scientific attention
over the recent years due to their nonlinear behavior and the risks of abrupt
state changes. While being stable over a large range of parameters, a tipping
element undergoes a drastic shift in its state upon an additional small
parameter change when close to its tipping point. Recently, the focus of
research broadened towards emergent behavior in networks of tipping elements,
like global tipping cascades triggered by local perturbations. Here, we analyze
the response to the perturbation of a single node in a system that initially
resides in an unstable equilibrium. The evolution is described in terms of
coupled nonlinear equations for the cumulants of the distribution of the
elements. We show that drift terms acting on individual elements and offsets in
the coupling strength are sub-dominant in the limit of large networks, and we
derive an analytical prediction for the evolution of the expectation (i.e., the
first cumulant). It behaves like a single aggregated tipping element
characterized by a dimensionless parameter that accounts for the network size,
its overall connectivity, and the average coupling strength. The resulting
predictions are in excellent agreement with numerical data for Erd\"os-R\'enyi,
Barab\'asi-Albert and Watts-Strogatz networks of different size and with
different coupling parameters
How motifs condition critical thresholds for tipping cascades in complex networks: Linking Micro- to Macro-scales
In this study, we investigate how specific micro interaction structures
(motifs) affect the occurrence of tipping cascades on networks of stylized
tipping elements. We compare the properties of cascades in Erd\"os-R\'enyi
networks and an exemplary moisture recycling network of the Amazon rainforest.
Within these networks, decisive small-scale motifs are the feed forward loop,
the secondary feed forward loop, the zero loop and the neighboring loop.
Of all motifs, the feed forward loop motif stands out in tipping cascades
since it decreases the critical coupling strength necessary to initiate a
cascade more than the other motifs. We find that for this motif, the reduction
of critical coupling strength is 11% less than the critical coupling of a pair
of tipping elements. For highly connected networks, our analysis reveals that
coupled feed forward loops coincide with a strong 90% decrease of the critical
coupling strength.
For the highly clustered moisture recycling network in the Amazon, we observe
regions of very high motif occurrence for each of the four investigated motifs
suggesting that these regions are more vulnerable. The occurrence of motifs is
found to be one order of magnitude higher than in a random Erd\"os-R\'enyi
network.
This emphasizes the importance of local interaction structures for the
emergence of global cascades and the stability of the network as a whole
Basin stability and limit cycles in a conceptual model for climate tipping cascades
Tipping elements in the climate system are large-scale subregions of the
Earth that might possess threshold behavior under global warming with large
potential impacts on human societies. Here, we study a subset of five tipping
elements and their interactions in a conceptual and easily extendable
framework: the Greenland and West Antarctic Ice Sheets, the Atlantic Meridional
Overturning Circulation (AMOC), the El-Nino Southern Oscillation (ENSO) and the
Amazon rainforest. In this nonlinear and multistable system, we perform a basin
stability analysis to detect its stable states and their associated Earth
system resilience. Using this approach, we perform a system-wide and
comprehensive robustness analysis with more than 3.5 billion ensemble members.
Further, we investigate dynamic regimes where some of the states lose stability
and oscillations appear using a newly developed basin bifurcation analysis
methodology. Our results reveal that the state of four or five tipped elements
has the largest basin volume for large levels of global warming beyond 4
{\deg}C above pre-industrial climate conditions. For lower levels of warming,
states including disintegrated ice sheets on West Antarctica and Greenland have
higher basin volume than other state configurations. Therefore in our model, we
find that the large ice sheets are of particular importance for Earth system
resilience. We also detect the emergence of limit cycles for 0.6% of all
ensemble members at rare parameter combinations. Such limit cycle oscillations
mainly occur between the Greenland Ice Sheet and AMOC (86%), due to their
negative feedback coupling. These limit cycles point to possibly dangerous
internal modes of variability in the climate system that could have played a
role in paleoclimatic dynamics such as those unfolding during the Pleistocene
ice age cycles.Comment: 50 pages, 10 figures, 2 table
Dynamics of Tipping Cascades on Complex Networks
Tipping points occur in diverse systems in various disciplines such as
ecology, climate science, economy or engineering. Tipping points are critical
thresholds in system parameters or state variables at which a tiny perturbation
can lead to a qualitative change of the system. Many systems with tipping
points can be modeled as networks of coupled multistable subsystems, e.g.
coupled patches of vegetation, connected lakes, interacting climate tipping
elements or multiscale infrastructure systems. In such networks, tipping events
in one subsystem are able to induce tipping cascades via domino effects. Here,
we investigate the effects of network topology on the occurrence of such
cascades. Numerical cascade simulations with a conceptual dynamical model for
tipping points are conducted on Erd\H{o}s-R\'enyi, Watts-Strogatz and
Barab\'asi-Albert networks. Additionally, we generate more realistic networks
using data from moisture-recycling simulations of the Amazon rainforest and
compare the results to those obtained for the model networks. We furthermore
use a directed configuration model and a stochastic block model which preserve
certain topological properties of the Amazon network to understand which of
these properties are responsible for its increased vulnerability. We find that
clustering and spatial organization increase the vulnerability of networks and
can lead to tipping of the whole network. These results could be useful to
evaluate which systems are vulnerable or robust due to their network topology
and might help to design or manage systems accordingly.Comment: 22 pages, 12 figure
Network motifs shape distinct functioning of Earth’s moisture recycling hubs
Earth's hydrological cycle critically depends on the atmospheric moisture flows connecting evaporation to precipitation. Here, we convert a decade of reanalysis-based moisture simulations into a high-resolution global directed network of spatial moisture provisions. We reveal global and local network structures that offer a new view of the global hydrological cycle. We identify four terrestrial moisture recycling hubs: the Amazon Basin, the Congo Rainforest, South Asia and the Indonesian Archipelago. Network motifs reveal contrasting functioning of these regions, where the Amazon strongly relies on directed connections (feed-forward loops) for moisture redistribution and the other hubs on reciprocal moisture connections (zero loops and neighboring loops). Earth's moisture recycling hubs are characterized by specific topologies shaping heterogeneous effects of land-use changes and climatic warming on precipitation patterns
Network motifs shape distinct functioning of Earth’s moisture recycling hubs
Earth's hydrological cycle critically depends on the atmospheric moisture flows connecting evaporation to precipitation. Here, we convert a decade of reanalysis-based moisture simulations into a high-resolution global directed network of spatial moisture provisions. We reveal global and local network structures that offer a new view of the global hydrological cycle. We identify four terrestrial moisture recycling hubs: the Amazon Basin, the Congo Rainforest, South Asia and the Indonesian Archipelago. Network motifs reveal contrasting functioning of these regions, where the Amazon strongly relies on directed connections (feed-forward loops) for moisture redistribution and the other hubs on reciprocal moisture connections (zero loops and neighboring loops). Earth's moisture recycling hubs are characterized by specific topologies shaping heterogeneous effects of land-use changes and climatic warming on precipitation patterns
Measuring tropical rainforest resilience under non-Gaussian disturbances
The Amazon rainforest is considered one of the Earth's tipping elements and
may lose stability under ongoing climate change. Recently a decrease in
tropical rainforest resilience has been identified globally from remotely
sensed vegetation data. However, the underlying theory assumes a Gaussian
distribution of forest disturbances, which is different from most observed
forest stressors such as fires, deforestation, or windthrow. Those stressors
often occur in power-law-like distributions and can be approximated by
-stable L\'evy noise. Here, we show that classical critical slowing
down indicators to measure changes in forest resilience are robust under such
power-law disturbances. To assess the robustness of critical slowing down
indicators, we simulate pulse-like perturbations in an adapted and conceptual
model of a tropical rainforest. We find few missed early warnings and few false
alarms are achievable simultaneously if the following steps are carried out
carefully: First, the model must be known to resolve the timescales of the
perturbation. Second, perturbations need to be filtered according to their
absolute temporal autocorrelation. Third, critical slowing down has to be
assessed using the non-parametric Kendall- slope. These prerequisites
allow for an increase in the sensitivity of early warning signals. Hence, our
findings imply improved reliability of the interpretation of empirically
estimated rainforest resilience through critical slowing down indicators