Environmental Engineering Reference
In-Depth Information
3.1
INTRODUCTION
The “uncertainty cascade”
Level of certainty
Low
Despite ongoing media and political debate, it is gener-
ally accepted scientifi cally that the Earth's climate is
changing and that human activities are, at least in part,
implicated in speeding up the rate of change (Intergov-
ernmental Panel on Climate Change (IPCC) 2007a).
Carbon dioxide concentrations in the atmosphere are
increasing more rapidly and to higher levels than ever
before experienced in human history, and climate
appears to be changing such that parts of the world are
experiencing record temperatures, changing rainfall
patterns, more frequent intense storms and so on.
While the existence and effects of a changing climate
are increasingly evident, the policy and management
responses at global and local levels are still under
intense debate. In addition, climate change comes as
the latest in a large array of changes being wrought on
the earth by human activity - land use change, trans-
port of species around the globe, pollution, land degra-
dation and resource over-use present an interacting set
of pressures on the world's ecosystems (Sala
et al
.
2000; Millennium Ecosystem Assessment (MA) 2005).
Climate change adds a further factor to this set of inter-
actions. In this chapter, I discuss
climate change
in
this context and examine what it means in the context
of ecosystem management and restoration. In particu-
lar, I focus on coping with uncertainties, the increasing
prevalence of
novel ecosystems
and the challenges
of devising, and choosing among, effective manage-
ment interventions.
High
Climate is changing
Human activities are a major cause
Likely regional/local changes
Likely impacts on ecosystems
Likely interactions with other changes
Possible management interventions
Possible policy responses
Figure 3.1
The uncertainty cascade.
about which there is increasing consensus and various
levels of uncertainty about others. One can view this
situation as an
uncertainty cascade
(Figure 3.1 ).
This schematic cascade starts with the basic premise
that climate is changing, and this premise has a high
degree of certainty - climates have changed in the past
and will continue to do so. It is now agreed that human
activities are currently of a magnitude and pervasive-
ness that it is fairly certain that humans are a causal
factor in recent and ongoing climatic change - however,
the complexity of the global climate system means that
there is still debate around the relative infl uence of
humans compared to other factors. This uncertainty is
at the heart of the public and political debate sur-
rounding climate change (Hulme 2009).
While there is near consensus in the scientifi c com-
munity that climate change is occurring, there is still
considerable uncertainty about how climate will
change in particular places. Climate models are con-
stantly being improved and the spatial resolution has
increased greatly over the last few decades, to the
extent that regional and local predictions are becoming
possible. Despite this, it remains diffi cult to provide cer-
tainty about the direction and magnitude of change in
rainfall and other important climatic parameters at
regional and local scales. This, in turn, causes consid-
erable uncertainty around what the impacts of climate
change will be on particular ecosystems, especially
when the potentially interacting effects of other factors
such as land use change, invasive species and so on are
also taken into account (Chapin
et al
. 2008 ).
Hence there is increasingly less certainty at local
scales and when management responses are consid-
3.2 THE UNCERTAINTY CASCADE:
WHAT WE KNOW AND WHAT WE
DON'T KNOW
Clearly there is a lot we still do not know about how
climate change will play out, how it will interact with
other global changes and how it will impact ecosys-
tems and human society. While levels of understand-
ing are likely to increase as more information becomes
available and climate models become more reliable,
there will still be considerable uncertainty surround-
ing all aspects of both the science and how manage-
ment and policy should respond. Uncertainty can be
viewed in many ways and can lead to endless debate,
controversy and lack of action. However, it is useful to
consider the levels of uncertainty associated with the
various aspects of climate change. There are elements
