Download - Act Talk - Vasilis Dakos: Expecting the unexpected

Vasilis Dakos

Aquatic Ecology and Water Quality Management Group Wageningen University, The Netherlands [email protected], (www.aew.wur.nl/UK/)

Expecting the unexpected:Leading indicators of regime shifts

Nordwijk March 2010

[transitions]

Vasilis Dakos Wageningen University Expecting the unexpected: Leading indicators of regime shifts


Clear lakes get turbid

Scheffer and Carpenter, 2003

algae dominated state

macrophyte dominated state


Cod in North Atlantic crashes


deMenocal et al, 2000

The Sahel turned into desert


Earth climate systems shift


Financial markets collapse


Ave

rage

jour

ney

time

We get stuck in traffic jams


Humans get epileptic seizures

Can we foresee if a system approaches a transition?


Can we foresee if a system approaches a transition?


Even if we do not understand the system?


Same shift different causes:

Small changes big surprisesBig changes big surprises

Critical transition

It depends…

Scheffer 2009


Critical Transitions workshop 2007

Early Warning Signals

for critical transitions

as Indicators of Resilience


Vasilis Dakos Wageningen University Expecting the unexpected: Leading indicators of regime shifts Scheffer and Carpenter, 2003

Why should we expect early-warning signals?

Bifurcation point

Eigenvalue goes to zero

Critical slowing down prior to a transition

Van Nes & Scheffer, 2007


What does the “eigenvalue goes-to-zero” mean?


Consequences of critical slowing down

Indicators of transitions in time



Rising variance

Carpenter & Brock, 2006



Guttal & Jayaprakash, 2008

Increasing skewness


Held & Kleinen, 2004


Increasing autocorrelation at-lag-1


Indicators of transitions in space



pattern formation

Rietkerk et al, 2004



Kéfi et al, 2007


Increasing grazing

Truncated power law

Spatial Variance

Spatial Skewness


Guttal & Jayaprakash, 2008

Spatial Mean


overexploited

underexploited

Dakos et al, early online



Increasing spatial correlation

Turbid state

Clear state


The indicators seem to work well on models…

23 juni 2005


Do the indicators work in reality?

But…

23 juni 2005


Slowing down precedes ancient climate shifts

Shutdown of thermohaline circulation

Model prediction Data

end of Younger Dryas

Dakos et al, 2008

23 juni 2005


Slowing down precedes ancient climate shifts

Dakos et al, 2008

…more examples

23 juni 2005


Increasing variance precedes epileptic attacks

McSharry et al, 2003; Scheffer et al, 2009

23 juni 2005


Increased spatial variance prior to community reorganization

Litzow et al, 2008

� Indirectestimates of resilience(indication of proximity to transition not predictive tools)

�Tools for verifying past regime shifts (indication in establishing a sudden change as a critical transition)

�Limitationsin their estimation in real systems (data length, data resolution, scale issues)

�Practical applicability:may work better in spatial than temporal context


Few concluding points

�How can we identify false positives? (need for proceedures to increase statistical power)

�What kind of monitoring schemesthat can capture the indicators do we need to design?

�Can we develop empirical tests for the indicators next to monitoring for probing the resilience of the system?

�Are they only relativemeasures? Or could an one-timesampling estimate indicate how much fragile the system is?

�How much early is early enough?


Challenges

23 juni 2005

[email protected]

Thank you for your attention!


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