Climate change futures: health, ecological and economic dimensions

CLIMATE CHANGE CAN
OCCUR ABRUPTLY
Perhaps the most daunting factor complicating the task
of estimating the future health and economic impacts
of climate change is that most climate futures and insurance
industry projections drastically underestimate the
rate at which climate might change.
on linear extrapolations of past trends and current trajectories,
though the insurance industry has long considered
“catastrophe theory” to project the impacts of
sudden, extreme losses. However, these models do not
predict the probabilities of such events. For climate,
increasing rates of change and greater volatility are
signs of instability and suggest greater propensity for
sudden change (Epstein and McCarthy 2004).
26 | THE CLIMATE CONTEXT TODAY
Most envisioned climate futures of international assessments
to date are based on gradual projections of
increasing temperatures. Some include temperature
variability, and others have begun to examine variance
in weather patterns. But most do not reflect the
high degree of variance in weather that is already
occurring and few address the potential consequences
of sudden change in impacts or abrupt shifts in climate
itself.
The notion that climate might change suddenly, or shift
from state to state, rather than change gradually —
what Richard Alley calls the “switch” rather than the
“dial” model for climate change — seemed like a radical
notion when it first began to take hold in the early
1990s. In nature, however, sudden shifts are the rule,
not the exception.
Steven J. Gould’s conception of evolution as “punctuated
equilibrium” depicts long periods of relative stability
with gradual change, punctuated by periods of mass
extinctions. These “interruptions” are then followed by
the explosion of new species with new solutions to
new environmental problems that fit together into new
communities of organisms.
On a more immediate time scale, non-linear changes
are part of our daily experience. When temperatures
change, liquid water can suddenly transform into a
hard, latticed structure as it freezes or vaporizes, when
it boils. Damage functions are also non-linear. For
example, hailstones tend to bounce off of windshields
until they reach a critical weight and break them.
Though abrupt climate change is a ubiquitous phenomenon
and is observed throughout ice, pollen, fossil
and geological records (NAS 2002), the bias toward
gradual, incremental change may reflect the constraints
of climate models that represent our best understanding
of how dynamic systems behave. Models have a difficult
time incorporating step-wise changes to new
states. Most industries naturally base their projections
Even more challenging is the observation that changes
in state can be triggered by small forces that approach
(often unforeseen) thresholds or “tipping points” — and
surpass them. Disease outbreaks can slowly grow in
impact, for example, then suddenly become epidemics.
For the climate, the transitions between glacial and
interglacial warm periods can involve changes from
5-10°C (9-18°F) in the span of a decade or less
(Steffan et al. 2004b). Sudden shifts are sometimes
restricted in geographic scope. At other times there are
global transformations (Severinghaus et al. 1998;
NAS 2002; Alley et al. 2003). Many such “high
impact” events that were considered “low probability”
just several years ago now seem to some increasingly
likely (Epstein and McCarthy 2004) or inevitable
(NAS 2002).
TIPPING POINTS
POSSIBLE “CLIMATE SHOCKS” WITH LIMITED
GEOGRAPHIC IMPACTS
• Small sections of Greenland, the West Antarctic Ice
Sheet (WAIS) or the Antarctic Peninsula could slip
into the ocean, raising sea levels several inches to
feet over years to several decades.
o Meltwater is seeping down through crevasses in
Greenland, lubricating the base of large glaciers
(Krabill et al. 1999; ACIA 2005).
o “Rivers of ice” in the WAIS are accelerating
toward the Southern Ocean (Shepherd et al.
2001; Payne et al. 2004; Thomas et al. 2004).
o Recent loss of floating ice shelves along the
Antarctic Peninsula removes back pressure from the
land-based ice sheets (Rignot and Thomas 2002).
• Alpine glacial melting could accelerate, inundating
communities below and diminishing water supplies
for nations dependent on this source for freshwater.