Because of the holidays, I did not get an immediate response
from several climate experts I contacted following
Nels Sultan’s comments about sea level rise in a blog post
Earth at the winter solstice, Dec.
22, 2011 / NOAA photo
If you recall, Nels was making the point that the sea level in
Seattle has been rising at a steady rate of .68 feet, or about 8
inches, per century since 1898, as reported by the
National Oceanic and Atmospheric Administration.
His post included this statement:
“There is no real basis for the claims that sea levels will rise
by 2.6 feet or 7 feet, or more. Globally, sea level rise has NOT
accelerated. As found and reported by many researchers who
specialize in this, including the eminent professor Bob Dean and
other coastal experts.”
As a reporter, I’m not inclined to shoot back a response. I’d
rather discuss the issue with experts in the field. That is what I
did, and I think I have a better handle on the issue.
What I’m hearing is that the original estimates by the
Intergovernmental Panel on Climate Change — a rise of between 7
inches and 2 feet by the end of the century — remain reasonable,
but conservative given that they did not account for increased
melting of the Greenland ice sheet. See this
explanation by Stefan Rahmstorf soon after the release of the
2007 IPCC report. By the way, the range above accounts for the
minimum and maximum across six climate-change scenarios.
Ever since, researchers have been trying to find ways to account
for the melting of the Greenland ice sheet, but the uncertainties
remain high. A widely cited paper by
W.T. Pfeffer, J.T. Harper and S. O’Neel suggests that “most
likely” starting point for further refinement is .8 meter, or 31
inches, of sea level rise by 2100.
In some ways, the authors of the Pfeffer paper were trying to
limit some of the extremes being reported by others, so they
concluded that sea level rise could not be more than 6 feet by
2100. Some folks have reported 6 feet as the top of the range, as
unlikely as that extreme may be. Check out this explanation posed
Real Climate and this
response by Pfeffer and his collaborators.
As for the Houston-Dean paper that Nels Sultan mentioned, those
authors created “various problems” in their assumptions, according
to Eric Steig, professor of Earth and Space Sciences at the
University of Washington. One major problem was the starting date
of 1930, as explained by
Stefan Rahmstorf in Real Climate:
“Other start dates either before or after this minimum show
positive acceleration. Picking 1930 for this analysis is thus a
classic cherry-pick, and according to the authors that is no
accident. They write in the paper: ‘Since the worldwide data of
Church and White (2006)…appear to have a linear rise since around
1930, we analyzed the period 1930 to 2010.’ The interval was thus
hand-picked to show a linear rise rather than acceleration.
“Houston & Dean use their result to question the future
acceleration of sea level rise predicted by Vermeer & Rahmstorf
(2009) for the 21st Century as a consequence of global warming.
They argue that the 1930s acceleration minimum calls into question
the semi-empirical link between global temperature and global sea
level proposed by us in that paper. However, it is clear they never
bothered to check this, because quite the opposite is the case: our
semi-empirical formula predicts this acceleration minimum,
as the graph above shows. As it turns out, this is an expected
outcome of the mid-20th-Century plateau in global temperature.”
I also discussed this issue of sea level rise with Lara Whitely
Binder, outreach specialist for the UW’s Climate Impacts Group.
While sea level rise means one thing on the world scale, she told
me, the local impacts can be quite different.
If you live in Neah Bay on the Olympic Peninsula, for example,
you are not likely to see any sea level rise until at least 2080.
That’s because the entire land mass is uplifting as a result of
movement along the tectonic plates, and the uplift is predicted to
be faster than sea level rise until late in the century.
On the other hand, Central and South Puget Sound may not be
uplifting at all and could be sinking, which would intensify the
effects of sea level rise. Areas built on fill, including portions
of Olympia, also could be sinking as the fill settles, Lara
In addition to global rise in sea level and local tectonic
shifts, factors affecting regional sea level rise include thermal
expansion of ocean waters and changes in onshore and offshore wind
During El Niño events, sea level can rise as much as 12 inches
for several months at a time. The Climate Impacts Group analyzed
more than 30 scenarios from global climate models and concluded
that the change in wind patterns as a result of climate change
could decrease sea level by as much as 1 inch or possibly increase
it by as much as 6 inches. Review the white paper
“Sea Level Rise in the Coastal Waters of Washington State” (PDF 2.4
mb) for more details.
How much an individual property is affected by sea level rise
depends on the slope of the beach. Given the same rate of rise,
water will affect a house sooner when it is built on a gradually
sloping beach as opposed to a steep slope. In any case, tides and
weather will always play a major role in water levels.
Lara told me that a group of West Coast researchers is working
on a new report about sea level for publication later this year by
the National Academy of Sciences. I’ll try to review that paper
when it comes out.
I wish to thank Eric Steig, Lara Whitely Binder, Cliff Mass,
David Montgomery and Nate Mantua for responding to my inquiry.
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