Ricarda Winkelmann | Potsdam Institute for Climate Impact Research (original) (raw)
Papers by Ricarda Winkelmann
The Cryosphere Discussions, 2021
Abstract. Surface melting of the Greenland Ice Sheet contributes a large amount to current and fu... more Abstract. Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea-level rise. Increased surface melt, algae growth, debris, and dust deposition lower the reflectivity of the ice surface and thereby increase melt rates: the so-called melt-albedo feedback describes this potentially self-sustaining increase in surface melting. Here we present a simplified version of the diurnal Energy Balance Model (dEBM-simple) which is implemented as a surface melt module in the Parallel Ice Sheet Model (PISM). dEBM-simple is a modification of diurnal Energy Balance Model (dEBM), a surface melt scheme of intermediate complexity useful for simulations over centennial to multi-millennial timescales. dEBM-simple is computationally efficient, suitable for standalone ice-sheet modeling and includes a simple representation of the melt-albedo feedback. Using dEBM-simple and PISM, we find that this feedback increases ice loss until 2300 through surface warming by 60 % ...
<p>Effective climate change mitigation necessitates swift societal transformations in order... more <p>Effective climate change mitigation necessitates swift societal transformations in order to meet the goals of the Paris Accord and to prevent abrupt, irreversible, transitions in the Earth System. Social tipping processes, where relatively small groups trigger sudden qualitative shifts in collective behaviour have been identified as a potential key mechanism instigating these necessary transformations.  However, the specific processes whereby experienced or anticipated future climate impacts effect large-scale societal changes remain largely unidentified and underrepresented in contemporary Earth System models. Here, we combine output from the MAGICC climate model, country-level social survey data and a low-dimensional network-based threshold model of social tipping to exemplify a transformative pathway in which climate change concern increases the potential for social tipping and extended anticipatory time horizons of future sea level rise shift the system closer towards a critical state whereby interventions, such as emergent social movements or policy change, can ultimately kick the system into a qualitatively different state. While dynamics of climate tipping elements are often reduced to a single control parameter, our findings suggest that such an approach may be inapplicable for social tipping processes, as single parameters alone may not reach critical thresholds required for tipping. Instead, we show that comparatively smaller changes in a set of multiple parameters can suffice to shift a system into its critical state where ephemeral (potentially deliberate) kicks can bring about social tipping. Tipping in the climate system is commonly associated with bifurcations, while social tipping processes are instead more likely induced by sudden events or shocks, where the required magnitudes of such kicks emerge from multiplicative, interacting factors. Effective analyses of such processes therefore requires novel modeling paradigms, specifically accounting for the increased complexity of socio-economic systems.</p>
Geoscientific Model Development Discussions, 2020
Abstract. The past and future evolution of the Antarctic Ice Sheet is largely controlled by inter... more Abstract. The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high resolution configurations, limiting these studies to individual glaciers or regions over short time scales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM with the global ocean general circulation model MOM5 via the ice-shelf cavity module PICO. Since ice-shelf cavities are not resolved by MOM5, but parameterized with the box model PICO, the framework allows the ice sheet and ocean model to be run at resolution of 16 km and 3 degree, respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the entire Antarctic Ice Sheet and the Earth system over time spans on the order of centuries ...
Melt rates from Antarctic ice shelves are determined by the temperature and salinity of the ambie... more Melt rates from Antarctic ice shelves are determined by the temperature and salinity of the ambient ocean. In many parts, ice shelves are shielded by clearly defined density fronts which keep relatively warm Northern water from entering the cavity underneath the ice shelves (Jacobs et al., 1992; Alley et al., 2015). Projections show that a redirection of coastal currents might allow these warmer waters to intrude into ice shelf cavities, for instance in the Weddell Sea (Hellmer et al., 2012, 2017), and thereby cause a strong increase in sub-shelf melt rates.
The Antarctic Ice Sheet is by far the largest potential source of future sea-level change, storin... more The Antarctic Ice Sheet is by far the largest potential source of future sea-level change, storing approximately 58 m sea-level equivalent. Its past and future evolution is thus of primary importance for coastal communities, infrastructure and ecosystems worldwide. To this day, the complex dynamics of the ice sheet and its surrounding ice shelves are one of the key challenges for sea-level projections. Recent observations show that part of the West Antarctic Ice Sheet is rapidly retreating, and that this retreat is likely irreversible on human timescales. Other regions are currently protected by ice plugs which hinder the onset of a dynamic instability. We will discuss the underlying mechanisms and potential critical thresholds for triggering persistent and possibly rapid ice discharge from Antarctic basins. As a consequence of these processes, sea-level might continue to rise for centuries or millennia. The magnitude and rate of ice loss depend critically on the warming trajectory and the feedbacks between the ice-sheet and the surrounding atmosphere and ocean.
A major difficulty encountered in estimating future sea-level rise is the potentially changing dy... more A major difficulty encountered in estimating future sea-level rise is the potentially changing dynamic contribution from the Antarctic Ice Sheet. One of the most critical factors determining the Antarctic mass budget, if not the decisive one, is the melting below ice shelves which influences the ice flow across the grounding line. Recent observations (e.g. Pritchard et al., 2012) and model simulations (e.g. Bindschadler et al., 2013) show that subshelf melting induced by a warming ocean caused additional ice flow across the grounding line and dominated the sea-level contribution from Antarctica in the past decades.
The ice-parameter sensitivity for a number of perturbations of the boundary of the Antarctic ice ... more The ice-parameter sensitivity for a number of perturbations of the boundary of the Antarctic ice sheet within the SeaRISE project is investigated for the Parallel Ice Sheet Model (PISM). The model incorporates a shallow approximation of the stress balance including the potential to model ice streams and the backstress of ice shelves on grounded ice. The dynamic enhancement of the flux across the grounding line caused by additional sub-shelf melting, reduced basal friction, enhanced net accumulation or surface warming, is sensitive to ice parameters for ice flow and sliding. The resulting model spread is large in the experiments with reduced basal friction, where after a strong initial response the ice discharge settles towards a new equilibrium. In the experiments with enhanced sub-shelf melting, the grounded-ice response is delayed by over a century, because the forcing itself acts on the ice shelves first and is then dynamically transmitted into the ice sheet. The experiments with...
SSRN Electronic Journal
Societal transformations are necessary to address critical global challenges, such as mitigation ... more Societal transformations are necessary to address critical global challenges, such as mitigation of anthropogenic climate change and reaching UN sustainable development goals. Recently, social tipping processes have received increased attention, as they present a form of social change whereby a small change can shift a sensitive social system into a qualitatively different state due to strongly self-amplifying (mathematically positive) feedback mechanisms. Social tipping processes have been suggested as key drivers of sustainability transitions emerging in the fields of technological and energy systems, political mobilization, financial markets and sociocultural norms and behaviors. Drawing from expert elicitation and comprehensive literature review, we develop a framework to identify and characterize social tipping processes critical to facilitating rapid social transformations. We find that social tipping processes are distinguishable from those of already more widely studied climate and ecological tipping dynamics. In particular, we identify human agency, socialinstitutional network structures, different spatial and temporal scales and increased complexity as key distinctive features underlying social tipping processes. Building on these characteristics, we propose a formal definition for social tipping processes and filtering criteria for those processes that could be decisive for future trajectories to global sustainability in the Anthropocene. We illustrate this definition with the European political system as an example of potential social tipping processes, highlighting the potential role of the FridaysForFuture movement. Accordingly, this analytical framework for social tipping processes can be utilized to illuminate mechanisms for necessary transformative climate change mitigation policies and actions.
Environmental Research Letters
Based on suggested interactions of potential tipping elements in the Earth’s climate and in ecolo... more Based on suggested interactions of potential tipping elements in the Earth’s climate and in ecological systems, tipping cascades as possible dynamics are increasingly discussed and studied as their activation would impose a considerable risk for human societies and biosphere integrity. However, there are ambiguities in the description of tipping cascades within the literature so far. Here we illustrate how different patterns of multiple tipping dynamics emerge from a very simple coupling of two previously studied idealized tipping elements. In particular, we distinguish between a two phase cascade, a domino cascade and a joint cascade. While a mitigation of an unfolding two phase cascade may be possible and common early warning indicators are sensitive to upcoming critical transitions to a certain degree, the domino cascade may hardly be stopped once initiated and critical slowing down–based indicators fail to indicate tipping of the following element. These different potentials for...
Tipping elements are nonlinear subsystems of the Earth system that can potentially abruptly and i... more Tipping elements are nonlinear subsystems of the Earth system that can potentially abruptly and irreversibly shift if environmental change occurs. Among these tipping elements is the Amazon rainforest, which is threatened by anthropogenic activities and increasingly frequent droughts. Here, we assess how extreme deviations from climatological rainfall regimes may cause local forest-savanna transitions that cascade through the coupled forest-climate system. We develop a dynamical network model to uncover the role of atmospheric moisture recycling in such tipping cascades. We account for the heterogeneity in critical thresholds of the forest caused by adaptation to local climatic conditions. Our results reveal that, despite this adaptation, increased dry-season intensity may trigger tipping events particularly in the southeastern Amazon. Moisture recycling is responsible for one-fourth of the tipping events. If the rate of climate change exceeds the adaptive capacity of some parts of ...
Geoscientific Model Development
The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions be... more The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high-resolution configurations, limiting these studies to individual glaciers or regions over short timescales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM (Parallel Ice Sheet Model) with the global ocean general circulation model MOM5 (Modular Ocean Model) via the ice shelf cavity model PICO (Potsdam Ice-shelf Cavity mOdel). As ice shelf cavities are not resolved by MOM5 but are parameterized with the PICO box model, the framework allows the ice sheet and ocean components to be run at resolutions of 16 km and 3 • respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the Antarctic Ice Sheet and the global ocean over time spans of the order of centuries to millennia. In this study, we describe the technical implementation of this coupling framework: sub-shelf melting in the ice sheet component is calculated by PICO from modelled ocean temperatures and salinities at the depth of the continental shelf, and, vice versa, the resulting mass and energy fluxes from melting at the ice-ocean interface are transferred to the ocean component. Mass and energy fluxes are shown to be conserved to machine precision across the considered component domains. The implementation is com-putationally efficient as it introduces only minimal overhead. Furthermore, the coupled model is evaluated in a 4000 year simulation under constant present-day climate forcing and is found to be stable with respect to the ocean and ice sheet spin-up states. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions, and timescales between the ice and ocean component in a generic way; thus, it can be adopted to a wide range of model setups .
. Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribu... more . Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribution. In diminishing the buttressing force of the ice shelves that fringe the ice sheet the melting increases the solid-ice discharge into the ocean. Here we contrast the influence of basal melting in two different ice-shelf regions on the time-dependent response of an idealized, inherently buttressed ice-sheet-shelf system. Carrying out three-dimensional numerical simulations, the basal-melt perturbations are applied close to the grounding line in the ice-shelf's 1) ice-stream region, where the ice shelf is fed by the fastest ice masses that stream through the upstream bed trough and 2) shear margins, where the ice flow is slower. The results show that melting below one or both of the shear margins can cause a decadal to centennial increase in ice discharge that is more than twice as large compared to a similar perturbation in the ice-stream region. We attribute this to the fact that melt-induced ice-shelf thinning in the central grounding-line region is attenuated very effectively by the fast flow of the central ice stream. In contrast, the much slower ice dynamics in the lateral shear margins of the ice shelf facilitate sustained ice-shelf thinning and thereby foster buttressing reduction. Regardless of the melt location, a higher melt concentration toward the grounding line generally goes along with a stronger response. Our results highlight the vulnerability of outlet glaciers to basal melting in stagnant, buttressing-relevant ice-shelf regions, a mechanism that may gain importance under future global warming.
Global Sustainability
Non-technical summary We summarize some of the past year's most important findings within cli... more Non-technical summary We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements. Technical summary A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to st...
New Journal of Physics
Tipping elements in the climate system are large-scale subregions of the Earth that might possess... more 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 Ice Sheets (GIS) and West Antarctic Ice Sheets, the Atlantic meridional overturning circulation (AMOC), the El-Niño Southern Oscillation 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. By combining these two methodologies with a large-scale Monte Carlo approach, we are able to propagate the many uncertainties associated with the critical temperature thresholds and the interaction strengths of the tipping elements. 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 • C above pre-industrial climate conditions, representing a highly undesired state where a majority of the tipping elements reside in the transitioned regime. 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 GIS 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.
The European Physical Journal Special Topics
Tipping elements occur in various systems such as in socio-economics, ecology and the climate sys... more Tipping elements occur in various systems such as in socio-economics, ecology and the climate system. In many cases, the individual tipping elements are not independent of each other, but they interact across scales in time and space. To model systems of interacting tipping elements, we here introduce the PyCascades open source software package for studying interacting tipping elements (10.5281/zenodo.4153102). PyCascades is an object-oriented and easily extendable package written in the programming language Python. It allows for investigating under which conditions potentially dangerous cascades can emerge between interacting dynamical systems, with a focus on tipping elements. With PyCascades it is possible to use different types of tipping elements such as double-fold and Hopf types and interactions between them. PyCascades can be applied to arbitrary complex network structures and has recently been extended to stochastic dynamical systems. This paper provides an overview of the ...
The European Physical Journal Special Topics
The Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest are potential ti... more The Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest are potential tipping elements of the Earth system, i.e., they may respond with abrupt and potentially irreversible state transitions to a gradual change in forcing once a critical forcing threshold is crossed. With progressing global warming, it becomes more likely that the Amazon will reach such a critical threshold, due to projected reductions of precipitation in tropical South America, which would in turn trigger vegetation transitions from tropical forest to savanna. At the same time, global warming has likely already contributed to a weakening of the AMOC, which induces changes in tropical Atlantic sea-surface temperature (SST) patterns that in turn affect rainfall patterns in the Amazon. A large-scale decline or even dieback of the Amazon rainforest would imply the loss of the largest terrestrial carbon sink, and thereby have drastic consequences for the global climate. Here, we assess the direct...
The Cryosphere Discussions, 2021
Abstract. Surface melting of the Greenland Ice Sheet contributes a large amount to current and fu... more Abstract. Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea-level rise. Increased surface melt, algae growth, debris, and dust deposition lower the reflectivity of the ice surface and thereby increase melt rates: the so-called melt-albedo feedback describes this potentially self-sustaining increase in surface melting. Here we present a simplified version of the diurnal Energy Balance Model (dEBM-simple) which is implemented as a surface melt module in the Parallel Ice Sheet Model (PISM). dEBM-simple is a modification of diurnal Energy Balance Model (dEBM), a surface melt scheme of intermediate complexity useful for simulations over centennial to multi-millennial timescales. dEBM-simple is computationally efficient, suitable for standalone ice-sheet modeling and includes a simple representation of the melt-albedo feedback. Using dEBM-simple and PISM, we find that this feedback increases ice loss until 2300 through surface warming by 60 % ...
<p>Effective climate change mitigation necessitates swift societal transformations in order... more <p>Effective climate change mitigation necessitates swift societal transformations in order to meet the goals of the Paris Accord and to prevent abrupt, irreversible, transitions in the Earth System. Social tipping processes, where relatively small groups trigger sudden qualitative shifts in collective behaviour have been identified as a potential key mechanism instigating these necessary transformations.  However, the specific processes whereby experienced or anticipated future climate impacts effect large-scale societal changes remain largely unidentified and underrepresented in contemporary Earth System models. Here, we combine output from the MAGICC climate model, country-level social survey data and a low-dimensional network-based threshold model of social tipping to exemplify a transformative pathway in which climate change concern increases the potential for social tipping and extended anticipatory time horizons of future sea level rise shift the system closer towards a critical state whereby interventions, such as emergent social movements or policy change, can ultimately kick the system into a qualitatively different state. While dynamics of climate tipping elements are often reduced to a single control parameter, our findings suggest that such an approach may be inapplicable for social tipping processes, as single parameters alone may not reach critical thresholds required for tipping. Instead, we show that comparatively smaller changes in a set of multiple parameters can suffice to shift a system into its critical state where ephemeral (potentially deliberate) kicks can bring about social tipping. Tipping in the climate system is commonly associated with bifurcations, while social tipping processes are instead more likely induced by sudden events or shocks, where the required magnitudes of such kicks emerge from multiplicative, interacting factors. Effective analyses of such processes therefore requires novel modeling paradigms, specifically accounting for the increased complexity of socio-economic systems.</p>
Geoscientific Model Development Discussions, 2020
Abstract. The past and future evolution of the Antarctic Ice Sheet is largely controlled by inter... more Abstract. The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high resolution configurations, limiting these studies to individual glaciers or regions over short time scales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM with the global ocean general circulation model MOM5 via the ice-shelf cavity module PICO. Since ice-shelf cavities are not resolved by MOM5, but parameterized with the box model PICO, the framework allows the ice sheet and ocean model to be run at resolution of 16 km and 3 degree, respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the entire Antarctic Ice Sheet and the Earth system over time spans on the order of centuries ...
Melt rates from Antarctic ice shelves are determined by the temperature and salinity of the ambie... more Melt rates from Antarctic ice shelves are determined by the temperature and salinity of the ambient ocean. In many parts, ice shelves are shielded by clearly defined density fronts which keep relatively warm Northern water from entering the cavity underneath the ice shelves (Jacobs et al., 1992; Alley et al., 2015). Projections show that a redirection of coastal currents might allow these warmer waters to intrude into ice shelf cavities, for instance in the Weddell Sea (Hellmer et al., 2012, 2017), and thereby cause a strong increase in sub-shelf melt rates.
The Antarctic Ice Sheet is by far the largest potential source of future sea-level change, storin... more The Antarctic Ice Sheet is by far the largest potential source of future sea-level change, storing approximately 58 m sea-level equivalent. Its past and future evolution is thus of primary importance for coastal communities, infrastructure and ecosystems worldwide. To this day, the complex dynamics of the ice sheet and its surrounding ice shelves are one of the key challenges for sea-level projections. Recent observations show that part of the West Antarctic Ice Sheet is rapidly retreating, and that this retreat is likely irreversible on human timescales. Other regions are currently protected by ice plugs which hinder the onset of a dynamic instability. We will discuss the underlying mechanisms and potential critical thresholds for triggering persistent and possibly rapid ice discharge from Antarctic basins. As a consequence of these processes, sea-level might continue to rise for centuries or millennia. The magnitude and rate of ice loss depend critically on the warming trajectory and the feedbacks between the ice-sheet and the surrounding atmosphere and ocean.
A major difficulty encountered in estimating future sea-level rise is the potentially changing dy... more A major difficulty encountered in estimating future sea-level rise is the potentially changing dynamic contribution from the Antarctic Ice Sheet. One of the most critical factors determining the Antarctic mass budget, if not the decisive one, is the melting below ice shelves which influences the ice flow across the grounding line. Recent observations (e.g. Pritchard et al., 2012) and model simulations (e.g. Bindschadler et al., 2013) show that subshelf melting induced by a warming ocean caused additional ice flow across the grounding line and dominated the sea-level contribution from Antarctica in the past decades.
The ice-parameter sensitivity for a number of perturbations of the boundary of the Antarctic ice ... more The ice-parameter sensitivity for a number of perturbations of the boundary of the Antarctic ice sheet within the SeaRISE project is investigated for the Parallel Ice Sheet Model (PISM). The model incorporates a shallow approximation of the stress balance including the potential to model ice streams and the backstress of ice shelves on grounded ice. The dynamic enhancement of the flux across the grounding line caused by additional sub-shelf melting, reduced basal friction, enhanced net accumulation or surface warming, is sensitive to ice parameters for ice flow and sliding. The resulting model spread is large in the experiments with reduced basal friction, where after a strong initial response the ice discharge settles towards a new equilibrium. In the experiments with enhanced sub-shelf melting, the grounded-ice response is delayed by over a century, because the forcing itself acts on the ice shelves first and is then dynamically transmitted into the ice sheet. The experiments with...
SSRN Electronic Journal
Societal transformations are necessary to address critical global challenges, such as mitigation ... more Societal transformations are necessary to address critical global challenges, such as mitigation of anthropogenic climate change and reaching UN sustainable development goals. Recently, social tipping processes have received increased attention, as they present a form of social change whereby a small change can shift a sensitive social system into a qualitatively different state due to strongly self-amplifying (mathematically positive) feedback mechanisms. Social tipping processes have been suggested as key drivers of sustainability transitions emerging in the fields of technological and energy systems, political mobilization, financial markets and sociocultural norms and behaviors. Drawing from expert elicitation and comprehensive literature review, we develop a framework to identify and characterize social tipping processes critical to facilitating rapid social transformations. We find that social tipping processes are distinguishable from those of already more widely studied climate and ecological tipping dynamics. In particular, we identify human agency, socialinstitutional network structures, different spatial and temporal scales and increased complexity as key distinctive features underlying social tipping processes. Building on these characteristics, we propose a formal definition for social tipping processes and filtering criteria for those processes that could be decisive for future trajectories to global sustainability in the Anthropocene. We illustrate this definition with the European political system as an example of potential social tipping processes, highlighting the potential role of the FridaysForFuture movement. Accordingly, this analytical framework for social tipping processes can be utilized to illuminate mechanisms for necessary transformative climate change mitigation policies and actions.
Environmental Research Letters
Based on suggested interactions of potential tipping elements in the Earth’s climate and in ecolo... more Based on suggested interactions of potential tipping elements in the Earth’s climate and in ecological systems, tipping cascades as possible dynamics are increasingly discussed and studied as their activation would impose a considerable risk for human societies and biosphere integrity. However, there are ambiguities in the description of tipping cascades within the literature so far. Here we illustrate how different patterns of multiple tipping dynamics emerge from a very simple coupling of two previously studied idealized tipping elements. In particular, we distinguish between a two phase cascade, a domino cascade and a joint cascade. While a mitigation of an unfolding two phase cascade may be possible and common early warning indicators are sensitive to upcoming critical transitions to a certain degree, the domino cascade may hardly be stopped once initiated and critical slowing down–based indicators fail to indicate tipping of the following element. These different potentials for...
Tipping elements are nonlinear subsystems of the Earth system that can potentially abruptly and i... more Tipping elements are nonlinear subsystems of the Earth system that can potentially abruptly and irreversibly shift if environmental change occurs. Among these tipping elements is the Amazon rainforest, which is threatened by anthropogenic activities and increasingly frequent droughts. Here, we assess how extreme deviations from climatological rainfall regimes may cause local forest-savanna transitions that cascade through the coupled forest-climate system. We develop a dynamical network model to uncover the role of atmospheric moisture recycling in such tipping cascades. We account for the heterogeneity in critical thresholds of the forest caused by adaptation to local climatic conditions. Our results reveal that, despite this adaptation, increased dry-season intensity may trigger tipping events particularly in the southeastern Amazon. Moisture recycling is responsible for one-fourth of the tipping events. If the rate of climate change exceeds the adaptive capacity of some parts of ...
Geoscientific Model Development
The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions be... more The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high-resolution configurations, limiting these studies to individual glaciers or regions over short timescales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM (Parallel Ice Sheet Model) with the global ocean general circulation model MOM5 (Modular Ocean Model) via the ice shelf cavity model PICO (Potsdam Ice-shelf Cavity mOdel). As ice shelf cavities are not resolved by MOM5 but are parameterized with the PICO box model, the framework allows the ice sheet and ocean components to be run at resolutions of 16 km and 3 • respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the Antarctic Ice Sheet and the global ocean over time spans of the order of centuries to millennia. In this study, we describe the technical implementation of this coupling framework: sub-shelf melting in the ice sheet component is calculated by PICO from modelled ocean temperatures and salinities at the depth of the continental shelf, and, vice versa, the resulting mass and energy fluxes from melting at the ice-ocean interface are transferred to the ocean component. Mass and energy fluxes are shown to be conserved to machine precision across the considered component domains. The implementation is com-putationally efficient as it introduces only minimal overhead. Furthermore, the coupled model is evaluated in a 4000 year simulation under constant present-day climate forcing and is found to be stable with respect to the ocean and ice sheet spin-up states. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions, and timescales between the ice and ocean component in a generic way; thus, it can be adopted to a wide range of model setups .
. Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribu... more . Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribution. In diminishing the buttressing force of the ice shelves that fringe the ice sheet the melting increases the solid-ice discharge into the ocean. Here we contrast the influence of basal melting in two different ice-shelf regions on the time-dependent response of an idealized, inherently buttressed ice-sheet-shelf system. Carrying out three-dimensional numerical simulations, the basal-melt perturbations are applied close to the grounding line in the ice-shelf's 1) ice-stream region, where the ice shelf is fed by the fastest ice masses that stream through the upstream bed trough and 2) shear margins, where the ice flow is slower. The results show that melting below one or both of the shear margins can cause a decadal to centennial increase in ice discharge that is more than twice as large compared to a similar perturbation in the ice-stream region. We attribute this to the fact that melt-induced ice-shelf thinning in the central grounding-line region is attenuated very effectively by the fast flow of the central ice stream. In contrast, the much slower ice dynamics in the lateral shear margins of the ice shelf facilitate sustained ice-shelf thinning and thereby foster buttressing reduction. Regardless of the melt location, a higher melt concentration toward the grounding line generally goes along with a stronger response. Our results highlight the vulnerability of outlet glaciers to basal melting in stagnant, buttressing-relevant ice-shelf regions, a mechanism that may gain importance under future global warming.
Global Sustainability
Non-technical summary We summarize some of the past year's most important findings within cli... more Non-technical summary We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements. Technical summary A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to st...
New Journal of Physics
Tipping elements in the climate system are large-scale subregions of the Earth that might possess... more 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 Ice Sheets (GIS) and West Antarctic Ice Sheets, the Atlantic meridional overturning circulation (AMOC), the El-Niño Southern Oscillation 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. By combining these two methodologies with a large-scale Monte Carlo approach, we are able to propagate the many uncertainties associated with the critical temperature thresholds and the interaction strengths of the tipping elements. 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 • C above pre-industrial climate conditions, representing a highly undesired state where a majority of the tipping elements reside in the transitioned regime. 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 GIS 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.
The European Physical Journal Special Topics
Tipping elements occur in various systems such as in socio-economics, ecology and the climate sys... more Tipping elements occur in various systems such as in socio-economics, ecology and the climate system. In many cases, the individual tipping elements are not independent of each other, but they interact across scales in time and space. To model systems of interacting tipping elements, we here introduce the PyCascades open source software package for studying interacting tipping elements (10.5281/zenodo.4153102). PyCascades is an object-oriented and easily extendable package written in the programming language Python. It allows for investigating under which conditions potentially dangerous cascades can emerge between interacting dynamical systems, with a focus on tipping elements. With PyCascades it is possible to use different types of tipping elements such as double-fold and Hopf types and interactions between them. PyCascades can be applied to arbitrary complex network structures and has recently been extended to stochastic dynamical systems. This paper provides an overview of the ...
The European Physical Journal Special Topics
The Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest are potential ti... more The Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest are potential tipping elements of the Earth system, i.e., they may respond with abrupt and potentially irreversible state transitions to a gradual change in forcing once a critical forcing threshold is crossed. With progressing global warming, it becomes more likely that the Amazon will reach such a critical threshold, due to projected reductions of precipitation in tropical South America, which would in turn trigger vegetation transitions from tropical forest to savanna. At the same time, global warming has likely already contributed to a weakening of the AMOC, which induces changes in tropical Atlantic sea-surface temperature (SST) patterns that in turn affect rainfall patterns in the Amazon. A large-scale decline or even dieback of the Amazon rainforest would imply the loss of the largest terrestrial carbon sink, and thereby have drastic consequences for the global climate. Here, we assess the direct...