Critical transitions are abrupt shifts in the state of
ecosystem
An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...
s, the
climate
Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...
, financial and economic systems or other
complex
Complex commonly refers to:
* Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe
** Complex system, a system composed of many components which may interact with each ...
dynamical systems
In mathematics, a dynamical system is a system in which a Function (mathematics), function describes the time dependence of a Point (geometry), point in an ambient space, such as in a parametric curve. Examples include the mathematical models ...
that may occur when changing conditions pass a critical or
bifurcation point
Bifurcation theory is the mathematical study of changes in the qualitative or topological structure of a given family of curves, such as the integral curves of a family of vector fields, and the solutions of a family of differential equations. M ...
. As such, they are a particular type of
regime shift
Regime shifts are large, abrupt, persistent changes in the structure and function of ecosystems, the climate, financial and economic systems or other complex systems.Lewontin, R. (1969) Meaning of Stability. ''Brookhaven Sym Biol'', 13Holling, C. ...
. Recovery from such shifts may require more than a simple return to the conditions at which a transition occurred, a phenomenon called
hysteresis
Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
. In addition to natural systems, critical transitions are also studied in psychology, medicine, economics, sociology, military, and several other disciplines.
Early-warning signals
Critical slow down
Significant efforts have been made to identify early-warning signals of critical transitions.
[Scheffer, M., et al. (2009) Early-warning signals for critical transitions. ''Nature'' 461, 53–59][Dakos, V., et al. (2008) Slowing down as an early warning signal for ]abrupt climate change
An abrupt climate change occurs when the climate system is forced to transition at a rate that is determined by the climate system energy-balance. The transition rate is more rapid than the rate of change of the external forcing, though it may ...
. ''P Natl Acad Sci Usa'' 105, 14308–14312[van Nes, E.H., and Scheffer, M. (2007) Slow recovery from perturbations as a generic indicator of a nearby catastrophic shift. ''Am. Nat.'' 169, 738–747] Systems approaching a bifurcation point show a characteristic behaviour called critical slowing down leading to an increasingly slow recovery from perturbations. This, in turn, may lead to an increase in (spatial or temporal) autocorrelation and variance, while variance spectra tend to lower frequencies,
and the 'direction of critical slowing down' in a system's state space may be indicative of a system's future state when delayed negative feedbacks leading to oscillatory or other complex dynamics are weak.
Researchers have explored early-warning signals in lakes, climate dynamics,
the Amazon rainforest,
[
* News article about the study: ] forests worldwide,
[
* News article: ] food webs, dry-land transitions and epilepsy attacks.
Examples
Studies show that more than three-quarters of Amazon rainforest has been losing resilience since the early 2000s as measured by CSD
and that tropical, arid and temperate forests are substantially losing resilience.
It has been proposed that a loss of resilience in forests "can be detected from the increased temporal autocorrelation (TAC) in the state of the system, reflecting a decline in recovery rates due to the critical slowing down (CSD) of system processes that occur at thresholds".
Flickering
The above approach (looking for critical slow down) is how most researchers assess if a critical transition is imminent. However, in highly stochastic (random) systems, alternative basins of attraction will be reached well before bifurcation points are reached. Perturbations might therefore cause the system to 'flicker' between the basins of attraction.
Examples
This idea has gained considerable interest in the last few years, somewhat entering the mainstream.
The idea has been applied widely, to studies of ecological resilience (such as eutrophication of a lake
) and to larger systems such as the potential collapse of the
Atlantic Meridional Overturning Circulation
The Atlantic meridional overturning circulation (AMOC) is the main ocean current system in the Atlantic Ocean.IPCC, 2021Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Sem ...
.
See also
* Tipping points in the climate system
* Deforestation and climate change
* Ecological resilience
* Ecological threshold
* Ecosystem collapse
* Cascade effect (ecology)
* Percolation theory
References
External links
*
* {{Cite news , date=2022-09-08 , title=Climate change: Six tipping points 'likely' to be crossed , language=en-GB , work=BBC News , url=https://www.bbc.com/news/science-environment-62838627
Systems theory