Geoscience Reference
In-Depth Information
interested in climate change construct scenarios of the future and identify the
nature of the uncertainties involved. As part of this exploration, the Great
Barrier Reef will be used as an example of the types of impacts and scenarios that
are likely if we continue along the pathway to a Four Degree World. This type
of approach has also been extended to coral reefs in the South East Asian and
Indo-Pacific regions (e.g. Hoegh-Guldberg, 2000; Hoegh-Guldberg et al., 2009).
Three types of information are used to construct ecosystem scenarios. The
first involves an in-depth understanding of the physiological tolerance of marine
organisms to key variables (e.g. sea temperature, alkalinity) that are changing
as the climate changes. This field of science is often referred to as 'stress
biology' and has a long history, stretching back to the beginnings of research
fields such as physiological ecology. The central paradigm of these fields is
that organisms are adapted to perform optimally within specific environments.
Understanding limits to their ability to tolerate environmental variability is
extremely important. Generally, organisms adjust their physiological behaviour
to optimise their operation within a 'coping range', which is defined by upper
and lower thresholds, beyond which organisms experience reduced performance
and ultimately increased mortality. For example, reef-building corals undergo
coral bleaching in laboratory experiments when they are exposed to temperatures
1-3°C above regional summer temperatures (Hoegh-Guldberg and Smith, 1989;
Glynn and D'croz, 1990). This allows important insights into what might happen
if seas surrounding reef-building corals increase another 1°C or more beyond
today.
The output of these experimental studies links directly to the observations
of how organisms and ecosystems respond to environmental change under field
conditions. Typically, this second type of information provides a more subtle
insight into the complex changes that are likely under changes to environmental
conditions. Going back to the example of coral reefs, the laboratory-based
conclusion that reef-building corals are sensitive to small temperature excur-
sions (1- 3°C) above the average summer maxima has been verified through
field observations that show that mass coral bleaching events occur under similar
levels of heat stress in the field (Strong et al., 1997; Hoegh-Guldberg, 1999
; Wilkinson and Hodgson, 1999). In addition to these types of observations,
there is also value in looking at the current distribution of coral reefs relative
to environmental factors (Kleypas et al., 1999). In this case, field evidence also
identifies potential combinations of environmental factors which limit the distri-
bution of a particular type of organism or community.
The last type of information that is used to construct scenarios involves
projections of how environmental conditions are likely to change. In this
respect, outputs of the community of General Circulation Models (GCMs) are
invaluable for constructing perspectives on how key environmental variables
within the environments are likely to change and a range of possible futures
can be explored (IPCC, 2007). This is especially powerful if multiple models
are used (e.g. CMIP5 models, Taylor et al., 2012). Combining this type of
information has led to the conclusion that coral reefs such as the Great Barrier
