Geoscience Reference
In-Depth Information
Event attribution often uses a method called fractional attribution. This method
tries to assess what fraction can be attributed to natural cycles and what can be
attributed to human infl uence on climate. This approach is based on the physical
understanding of the climate system and the individual hazard itself, on data com-
parison, as well as on climate models. Pall et al. (2011) and Min et al. (2011) applied
this method in their studies (see Sect.
2.3.3
).
The Interpreting Climate Conditions group at the Earth System Research
Laboratory's Physical Science Division from NOAA and the Attribution of Climate-
related Events group (ACE) as part of the Met Offi ce/Hadley Centre in collabora-
tion with NOAA have been established to forward this research arm.
Whereas the Interpreting Climate Conditions group is mainly focused on the
climate attribution of the United States, the ultimate goal of ACE is to establish an
international system that could provide timely, scientifi cally robust, and reliable
assessments of recent extreme events and the infl uence climate change has had on
them (Schiermeier
2011
).
2.3.2
Potential Issues
Event attribution cannot relate a specifi c event with absolute confi dence to human
causes. Extreme events are part of the natural climate system and have always
occurred, even when humans have not been present. Event attribution statements
therefore remain in the realm of possibilities and cannot deliver fi nite answers
(Nature 2011; Allen
2003
). This means that only the infl uence of factors on the
probability and intensity of an extreme event can be assessed (Stott et al.
2011
).
Event attribution is dependent on how well we understand the physics behind
extreme events (Stott et al.
2011
). Hence, some events like heat events are easier to
attribute than others (Schiermeier
2011
). Further, “[a]ttribution is only as good as
the models and statistics that power it” (Nature 2011). The results depend on the
model and the data availability, reliability, resolution, and length of historic records.
The results of event attribution also depend on the exact research question and
what the research tries to attribute: If it is the magnitude of an individual event or the
likelihood that a certain threshold is exceeded (Peterson et al.
2012
) (see Sect.
2.3.3
).
Lastly, a very important question is: what drives event attribution research? Is it
the goal to create a liability case for climate change extremes and their related costly
damage? Who do you sue in the aftermath of a fl ooding when the house prices fall?
(Allen
2003
).
Event attribution up until now can only produce probabilities; will that be enough to
make legal cases? This is not only a scientifi c question but also a legal one (Allen
2003
).
The big question is whether current greenhouse-gas emitters could ever be held liable for
the actual impacts of their emissions. (Allen
2003
)
Trenberth (
2012
) suggests that the attribution approach should be changed;
instead of having a null hypothesis that states that the human infl uence has no effect
on climate to a null hypothesis that recognizes the anthropogenic infl uence. As a
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