19.6.4. Climate Protection in an Irregular World
The predictability and manageability of singular phenomena is low. Their impacts
can be sudden, large, and irreversible on a time scale of centuries. Regularizing
such impacts would be an appropriate response, but this would require much better
understanding of the statistics and characteristics of the complex processes
involved. The presence of singularities therefore makes analytic and political
treatment of the climate change problem particularly difficult.
Little is known, in quantitative terms, about the potential damages that could
be inflicted by singularities on ecosystems and market sectors across the globe.
This deficit has two main reasons (see also Moss and Schneider, 2000). First,
extensive research on the causes, mechanisms, and impacts of singular events
in the context of climate change is just getting started. Second, mechanistic
and probabilistic analysis of complex nonlinear systems is more demandingby
orders of magnitudethan investigation of simple linear ones.
Figure 19-6: Stability of North Atlantic thermohaline circulation
(THC) computed with the CLIMBER model (Petoukhov et al., 2000). Degree of
shading indicates probability of THC collapse. Light shading denotes low
probability; dark shading denotes high probability. The higher the hydrological
sensitivity (HHS = high hydrological sensitivity, LHS = low hydrological
sensitivity), the faster the rate of temperature increase, or the greater
the magnitude of temperature increase, the more likely that the North Atlantic
THC becomes unstable.
The knowledge base for assessing consequences of singularities
will probably be broadened considerably over the next 5-10 years. Further
advances in simulation modeling soon will allow better projections of future
climate variability down to modified extreme events statistics (CLIVAR, 1998),
as well as better translations of those projections into impacts on natural
and societal systems (e.g., Weyant et al., 1996; Alcamo et al., 1998; Rotmans
and Dowlatabadi, 1998). Earth system analysis, as supported by the big international
research programsWorld Climate Research Programme (WCRP), International
Geosphere-Biosphere Programme (IGBP), and International Human Dimensions Programme
(IHDP)will bring about more complete understanding of macro-singularities
within the responses of the Earth system under pertinent forcing (Schellnhuber,
1999). A major source of information and comprehension, in this context, will
be evidence provided by paleorecords (IGBP, 1998). These scientific efforts
should assist the decisionmaking process by creating a clearer picture of the
future. Unfortunately, creating plausible projections is always tricky in practice
(Sarewitz et al., 2000).
A major challenge is to make responsible use of available information regarding
the likelihood and the consequences of conceivable singular events. Responsibility
here means the obligation of decisionmakers to make the "right" decision,
taking into account the diverse societal values and wide ranges of individual
interests that are at stake and that may be mutually contradictory. Thus, the
standard challenge is to develop proper policies under uncertainty (i.e., neither
ignorance nor omniscience) to achieve the objectives of the UNFCCC and to satisfy
affected stakeholders as well as possible.
A broad and intensive discourse on the ethical aspects of singular responses
to climate change (e.g., Markandya and Halsnaes, 2000; Munasinghe, 2000; Toth,
2000) is rediscovering many of the arguments put forward in traditional moral
philosophy and risk policy. Ethical and procedural aspects of this type have
been examined in various other contexts before, where certain concepts (such
as human rights) act as a constraint on economic activity (emphasizing utilitarian
goals), even when the cost-benefit ratio is unfavorable (e.g., the review of
the agricultural situation by Aiken, 1986).
One of the crucial questions is how to deal with high-consequence impacts that
may wipe out entire systems or cultures. Such non-implausible "nightmare"
or "doomsday" scenarios could result from the speculative but consistent
concatenation of individually possible causal relationships (e.g., Schellnhuber
and Yohe, 1997). A vexing question is whether the lack of credible scientific
evidence for such a scenario provides justification to ignore its possibility
completely. Some argue that such effects have to be avoided by all means, irrespective
of the economic burdens involved. Others argue that the uncertainties involved
do not provide enough support for extensive measures and their economic costs.
Within the climate-change framework, however, many incalculable risks could
be reduced considerably by more sensible measures. The debate on the "legitimacy"
of the different perspectives is impossible to resolve, however (Jasanoff, 1990).
The vague evidence provided by the present state of research supports the notion
that even relatively small changes in mean climate could lead to large changes
in the occurrence of stochastic extreme events. Furthermore, it suggests that
large-scale discontinuities are unlikely below a 2°C warming but relatively
plausible for a sustained warming of 8-10°C. The relatively small set
of investigations discussed above lead to the conclusion that a warming range
of 4-5°C seems to represent a critical disturbance regime where macro-discontinuities
may start to emerge. This temperature threshold appears to be sensitive to the
rate of change at which this level is reached.