Considering the above summary and the information

Considering the above summary and the information presented in this report the following
conclusions are appropriate:
• Climate is changing, but there is significant uncertainty regarding the magnitude of the
change over the design life of the systems and elements of our built environment. It will
be difficult to reliably estimate the change that will occur over several decades, long after
the infrastructure is built and the financing and governance have been established.
• The prediction of future extreme events with associated parameters and their frequency of
occurrence have even greater uncertainty and less reliability than projections of long-term
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Adapting Infrastructure and Civil Engineering Practice to a Changing Climate page 61
trends in temperature or precipitation. Downscaling does not reduce the uncertainty
inherent in GCM projections and most likely would increase the uncertainty.
• Probabilistic methods often have relied on the assumption of stationarity, which implies
the statistical properties of variables in future time periods will be similar to past time
periods. The use of this assumption has been challenged recently because future climate,
weather and their extremes are expected to be statistically different than in the past.
• Because the uncertainty associated with future climate is not completely quantifiable, it
may not be possible to employ a probabilistic risk-based approach and, therefore, if
projections of future climate are to be considered in engineering practice it will require
considerable engineering judgment.
Engineers build long-lived infrastructure. The right-of-ways and footprints of the infrastructure
have even longer-term influences. These facts suggest that the planning and design of new
infrastructure should account for the climate of the future. Considering the impacts of climate
change in engineering practice is analogous to including forecasts of long-term demands for
infrastructure use as a factor in design. However, even though the scientific community agrees
that climate is changing, there is significant uncertainty about the spatial and temporal
distributions of the changes over the lifetime of infrastructure designs and plans. The
requirement that engineering infrastructure meets future needs while taking into account the
uncertainty of future climate, and at the scale of the majority of engineering projects, leads to a
dilemma for practicing engineers. The dilemma is a gap between climate science and engineering
practice that must be bridged.
Infrastructure designs and plans, as well as institutions, regulations and standards to which they
must adhere, will need to accommodate a range of future climate conditions. Secondary effects
from a changing climate such as changes in land cover and land use, resource availability and
demographics in population will be similarly uncertain and will require flexibility in
infrastructure location and design. The standards, codes, regulations, zoning laws, etc., which
govern infrastructure are often finely negotiated or delicately balanced legally, which often
makes them slower to adapt. In addition, different stakeholders may exploit the uncertainties
associated with climate change to argue for positions they prefer.