Climate change futures: health, ecological and economic dimensions

• Thawing of permafrost (permanently frozen land)
could increase atmospheric concentrations of methane
and contribute to further global warming.
o Methane, while shorter lived than CO 2
, is 21
times more powerful as a greenhouse gas.
CANDIDATES FOR ABRUPT CLIMATE CHANGE
• Slippage of a large portion of Greenland or the
WAIS would raise sea levels many feet, inundating
coastal settlements throughout the world.
o Loss of all of Greenland or the WAIS (unlikely to
occur for centuries) would each raise sea levels
7 meters (21 feet).
• Release of methane from thawing Arctic and boreal
permafrost could suddenly force the climate into a
much warmer state (Stokstad 2004).
o The world’s largest frozen peat bog — a permafrost
region the size of France and Germany
combined, spanning the entire sub-Arctic region of
western Siberia — has begun to melt for the first
time since forming 11,000 years ago at the end
of the last ice age (Pearce 2005). The Alaskan
tundra is also thawing.
o Western Siberia has warmed an average of 3°C
(5.4°F) in the last 40 years, faster than almost anywhere
else on Earth. The west Siberian bog contains
some 70 billion tons of methane, a quarter of
all the methane stored on the earth’s land surface
(Pearce 2005).
• Changes in the North Atlantic (ice melting and rain
falling) could shut down the Gulf Stream and the
ocean conveyor belt, triggering a “cold reversal” that
alters climate in the Northern Hemisphere and the
Middle East (NAS 2002; ACIA 2005).
o The global impacts of such a shutdown might be
tempered by overall global warming.
• There may be a threshold level or “tipping point” for
Earth’s total reflectivity (albedo).
o The Earth’s overall albedo is now about 30%. If
enough ice melts and Earth’s albedo decreases to
28%, for instance, the increased heat entering the
oceans could potentially trigger a “runaway warming,”
with accelerated heating of Earth’s surface.
(Rignot and Thomas 2002; Rignot et al. 2004;
Cook et al. 2005).
The instabilities underlying the potential “tipping
points” are all present today — and they are not
occurring in isolation. Several of the changes depicted
could occur concurrently. Significant discharges of ice,
for example, could be accompanied by large releases
of methane. As modelers grapple with the potential for
step-wise changes in the climate system (Schellnhuber
2002), the potential for multiple, linked abrupt
changes to occur makes the outcomes and impacts of
accelerated change all the more uncertain.
Management, adaptation and mitigation strategies that
underestimate the potential for exponential change in
biological systems or abrupt change in climate are
unlikely to be successful. Substantially reducing greenhouse
gas emissions to stabilize the concentrations
could slow the rate of climate change and give the
system the chance to reach a new equilibrium.
THE CLIMATE CHANGE
FUTURES SCENARIOS
In order to envision the future impacts of climate
change, this study considers the potential for warming
to proceed gradually, but with growing variance in
weather. Both scenarios envision a climate context of
gradual warming with growing variability and more
weather extremes. Both scenarios are based on “business-as-usual,”
a scenario which, if unabated, would
lead to doubling of CO 2
from pre-industrial values by
midcentury. Extensive case studies described in Part II
of this report provide background on the various classes
of impacts. The first scenario calls for escalating
impacts, and this assessment examines the economic
dimensions of health and environmental impacts. The
second scenario envisions a future with widespread,
abrupt impacts. Note that these two scenarios are
about the potential impacts of climate change, not the
types of climate shocks or abrupt changes depicted
above. The first scenario implies grave consequences
for the global economy, while the widespread impacts
of the second would be devastating and most likely
unmanageable.
Regarding the worst-case scenario, the interested reader
may refer to the “Pentagon Scenario” (Schwartz
and Randall 2003) on abrupt climate change, which
forces the reader to “think the unthinkable.”
27 | THE CLIMATE CONTEXT TODAY