high tide. Levees and other defenses judged adequate to withstand foreseeable events today may be breached when stressed
by storms in the future, making it likely that the effect of rising
seas will be felt through increasingly likely extreme events.
If society waits until so-called 100-year events are experienced every decade, individuals and communities will suffer
needlessly, and the nationwide costs of responding will greatly
exceed the forgone costs of mitigation.
A study titled “Coastal flood damage and adaptation costs
under 21st century sea level rise” by Jochen Hinkel, et al., sum-
marizes the issue as follows (the numerical values are global):
Without adaptation, 0. 2-4.6% of global population is ex-
pected to be flooded annually under 25-123 cm of global
mean sea level rise, with expected annual losses of 0. 3-9.3%
of gross domestic product. Damages of this magnitude
are unlikely to be tolerated by society and adaptation will
be widespread. The global cost of protecting the coast
with dikes are significant … but much smaller than the
global cost of avoided damages even without account-
ing for indirect costs of damage to regional production
supply. (emphasis added).
A similar point was made by the Congressional Budget Office in “Potential Cost Savings from the Pre-Disaster Mitigation
Program,” a 2007 study that concluded that future losses are
reduced by about $3 for each $1 spent on FEMA’s pre-disaster
mitigation program (measured in discounted present value).
Findings such as this strongly argue for a long-range view
of coastal development and land use so that the benefits of
development (usually apparent in the near term due to increased economic activity) can be balanced with costs (often
not apparent in the near term due to increasing costs for risk
transfer or changing climatic conditions). There is ample
precedent for such an approach using previously cited analyses of Social Security and Medicare costs over a multi-decadal
An obvious first step in that process is to improve and use
tools to assess potential exposure, in particular estimates of
future inundation potential during the design lifetime of structures. As pointed out above, such tools are available. Gathering
this information and analysis will not halt development nor
force prohibitively expensive mitigation measures. Instead, development may be channeled into areas more easily defended
against rising seas; structures may be concentrated in order to
reduce the extent of required defenses; or individual building
characteristics may be adjusted. If ongoing coastal development
will require increased expenditures in coming decades for adaptation, at least such costs should be identified and planned for
before construction commences.
With regard to property or infrastructure already in place,
potential costs for adaptation should be understood so invest-
ments can be made gradually, minimizing disruption to the
economy. Doing so is analogous to adjusting taxes, benefits, or
the retirement age gradually to maintain the financial solidity
of the Social Security program. Ignoring needed investments in
coastal defenses until cities are experiencing ruinous flooding
is no more appropriate than ignoring problems with the Social
Security trust funds until cash runs out.
The key issue underlying this article and its companion “
Demographics, Development, and Disasters” is that the combination
of rapid development in high-risk areas and changing hazards is
combining to pose serious macroeconomic challenges for many
countries. Wealthy countries with large coastal populations such as
the United States or Australia have an opportunity to manage these
issues with a practicable mix of affordable adaptation strategies.
Developing countries with growing populations, increasing wealth,
and/or extreme hazards face a much more daunting challenge.
Melting glaciers and high-latitude ice can be easily observed,
making it hard to argue with predictions of future difficulties. A
reasonably clear scientific consensus exists as to the likely range
of future states. Fortunately, major problems are several decades
in the future. Tools exist that have proved effective in quantifying exposure and informing decisions about which adaptation
strategies are cost-effective. Regrettably, despite a number of
catastrophes that should have served as a wake-up call for action, relatively little is being done to make meaningful changes
in exposure or to invest in defenses.
Tackling this problem requires new ways of thinking, particularly with regard to building codes and land-use policies. We
face difficult choices, including abandoning property, restricting
development in coastal areas, significantly increasing requirements for mitigation (such as higher elevation requirements
on new and rebuilt structures), or investing tens of billions of
dollars in defenses. All of these options will generate strong opposition from various affected parties, making it likely that little
will be done until a series of disasters provides the impetus to
overcome inertia. Unfortunately, as we learned from Katrina,
ignoring warnings can be very expensive.
The successful example of a long-term planning process in
the Social Security and Medicare programs can serve as a road
map of how the government can analyze a problem with similar potential for long-term economic consequences and act to
reduce the likelihood of disaster. As is the case with social programs, relatively small changes made now can result in large
long-term benefits. If Ronald Reagan was able to raise taxes to
protect Social Security for future generations, perhaps a future
president can champion policies that require moderate sacrifice
in the short run to mitigate ruinous flooding in the future.
RADE MUSULIN is an Academy volunteer with decades of
research in this area who currently serves on the Academy’s
Extreme Events Committee.
1. NASA’s Earth Observatory; http://www.earthobservatory.nasa.gov/
2. Florida Sea Level Scenario Sketch Planning Tool; http://sls.geoplan.ufl.edu/
3. “Recommendations for Using Future-Conditions Hydrology for the National
Flood Insurance Program”; http://www.fema.gov/media-library-