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bjbj- Video Transcript Level Rise for the Coasts of California, Oregon, and Washington
Past, Present, Future National Research Council of the National Academies The National Research
Council has just completed a new report on sea level rise along the coast of California,
Oregon and Washington which is intended to provide elected officials, coastal managers,
and decision makers with an objective and independent analysis upon which they can base
future coastal planning. Sea levels are rising because the ocean is warming which increases
ocean volume, and also because ice sheets and glaciers are melting Over the past century
tide gages indicate that sea level has risen globally about 7 inches but over the last
20 yrs satellite measurements indicate that number has accelerated to nearly twice as
fast as its been over the last hundred years So the question is how much will sea level
rise over the next century? Although we have global sea level rise values, we know from
place to place that those values will vary depending on offshore oceanographic conditions
and whether the land is rising or sinking or is tectonically active, and along the west
coast we know we have an active coastline such that the land has been rising and sinking
which affects those local sea level rise values. From San Diego north to Cape Mendocino, we
know the coast of California which is the Pacific plate is sliding alongside the San
Andreas fault with very little vertical motion along the coast line such that sea level from
tide gages over the last century is close to the global number about 4-8 North of Cape
Mendocino, along the coast of Northern California, Oregon, and Washington, however, the land
has been slowly rising such that many of the tide gages actually show a small drop in sea
level over the last century or so This region lies along the Cascadia Subduction Zone, where
the Juan de Fuca Plate, descends or is subducted, beneath the North American Plate. This builds
up seismic strain along the coast, which actually pushes the land upward, and explains why sea
level in the region has dropped, even as global sea level has risen. This could all change
very rapidly however if we have a large offshore earthquake which could cause rapid subsidence
and therefore an instant rise in sea level. Observations and projections of both climate
change and sea level rise indicate that sea level rise is going to continue to rise well
into the future. There are uncertainties however and that makes precise predictions difficult.
The further we go out in time, the greater those uncertainties become The Committee projected
future regional sea levels, and they vary along the west coast. By 2030 our average
sea-level rise values for the area south of Cape Mendocino are projected to be about 6
inches, while to the north, only about 2 inches of rise is expected because the coastline
is slowly rising. By 2050, we project 12 inches orf rise to the south and 6 inches to the
north along the Oregon and Washington coasts; and by 2100, average values of 36 inches along
the California coast are projected, and 24 inches north of Cape Mendocino. These are
average values however and the actual values could be significantly higher or lower. For
some perspective, the two major international airports in San Francisco Bay, San Francisco
and Oakland, were built on fill only a few feet above sea level such that 16 inches of
sea level rise, which could happen within the next several decades, would begin to inundate
those runways. Many west coast communities already experience coastal erosion, flooding
and inundation, and loss of wetlands due to El Ni o elevated sea levels, the impacts of
large storm waves at times of high tide, and a slowly rising sea level. The water levels
reached during these short-term events have exceeded mean sea levels projected for 2100.
Thus, at least for the next several decades, these events are a greater hazard for the
west coast than the climate-driven rise in sea level. It is very likely that in the future
as sea level continues to rise, that the impacts of those events will get greater in magnitude
and also likely they will increase in frequency, as we move into the future. Coastal communities
need to begin to understand these processes and what these sea level rise indicate to
them and plan accordingly. gd E gd E gd E gd E gd E :p E [Content_Types].xml #!MB ;c=1
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