PIK Biennial Report 2000-2001 - Potsdam Institute for Climate ...

TOPIK 2 - Management of Singular Events
This TOPIK is concerned with extreme events, such as
severe storms, floods or droughts, and with abrupt
changes in the Earth system, such as the break-up of a
large ice sheet. Meteorite impacts or major volcanic
eruptions are further examples of singular events. They
are characterized by a major impact or change occurring
over a relatively short time, in contrast to insidious
GRAIN
Guardrails and Indicators for Climate Protection
Project speaker: Elmar Kriegler
PIK project members: Nico Bauer, Ottmar Edenhofer,
Hermann Held, Thomas Kleinen, Elmar Kriegler,
Gerhard Petschel-Held.
External project collaborators: Thomas Bruckner,
(Technical University Berlin).
Motivation
The GRAIN project addresses the issue of robust climate
protection strategies under uncertainty and nonlinearity.
How can we account for the large uncertainty
about the complex human-environment system? How
can we detect possible indicators of nonlinear thresholds?
Which structural changes of the socio-economic
system are needed to address climate change?
Decision under Uncertainty and Imprecision
The objective uncertainty about climate change can in
many cases not be quantified by precise probabilities.
Hence we are investigating theories which allow us to
capture not only uncertainty, but also imprecision. We
are particularly interested in the implications for decision-making;
with imprecise information the decisionmaker
can adopt a range of equally rational attitudes
ranging from a pessimist to an optimist perspective. Preliminary
results show that the decision-making model
behaves rather pessimistically, if there exists an intolerable
domain of future developments which has to be
strictly avoided.
Indicators of Critical Thresholds
Nonlinear effects, such as bifurcations and thresholds,
can be very important for the behaviour of the climate
system. As a prominent example we consider the North
Atlantic thermohaline circulation (THC). The THC
trends. Singular events can have a particularly damaging
effect on natural and socio-economic systems. This
TOPIK aims at characterizing singular events with
respect to their mechanisms and potential consequences,
at defining and assessing associated risks, and at developing
mitigation and adaptation strategies.
Fig. 1: The "typical" red spectrum becomes much “redder” close to
the bifurcation and may even change to an algebraic relationship.
breaks down if the freshwater input into the North
Atlantic basin reaches a critical value. This behaviour has
been observed both in conceptual models and GCMs.
We are investigating the simplest model of the THC, the
2-box Stommel model. The model undergoes a bifurcation
at a critical freshwater flux � c. We have added a stochastic
freshwater flux with mean value �. Figure 1
shows that the power spectral density of the circulation
strength changes markedly when the system approaches
the bifurcation. We are investigating whether this
method can be applied to other systems and be used as
an indicator for critical thresholds.
Technology and Investment
The energy system today is based on fossil fuels. To limit
emissions we have three strategic options:
1) Efficiency: increasing the energy efficiency,
2) Substitution: conversion to renewable energy,
3) Sufficiency: stabilizing consumption.
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