NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Sea level rise (off-topic)
From: Geoffrey Kolbe
Date: 2006 Jul 11, 13:57 -0500
Hello Frank.
Yes, I have seen looked at the link you gave for
the sea level graphs, and in particular at the
Mean Sea Level (MSL) data for "The Battery" in
New York. The website shows a graph of MSL
derived from measurements taken at The Battery
from 1856 up to 1999 (with a break in the
1880's). There is a straight line fit to the data
which shows a mean sea level rise of 2.77mm/year.
By comparison, the MSL trend for Liverpool since 1850 is 1.23mm/year.
Eyeballing data like this to look for trends away
from the linear is not the most ideal method of
analysis, as I am sure you will agree. It is
difficult to see trends less than about one
standard deviation - and this set of data is
pretty noisy. Without deeper and more
sophisticated statistical analysis, I don't think
you are justified in saying, "… there is no
evidence for any upswing at the end of the 20th century."
At the Proudman Oceanographic Laboratory there
are people who spend their time doing just this
sort of statistical analysis and I contacted
Professor Philip Woodworth at the POL to ask him
about higher order trends in the data. He tells
me that it is possible to extract an
"acceleration" of 0.78 +/- 0.3 mm/year/century
for the New York Battery data. For Liverpool
since 1850 it is 0.82 +/- 0.36 mm/year/century -
which is in good agreement. For Amsterdam,
Stockholm, Brest (France) and Sheerness
respectively, the accelerations are 0.42, 0.45,
0.44 and 0.84. And to show the international
nature of these accelerations we can head back to
the United States where San Francisco shows an
acceleration of 1.62 mm/year/century since 1855.
(But the tectonics of the West Coast probably put
a question mark on this number.)
The point is that all these accelerations are of
a very similar order. Each one by themselves
proves nothing, but taken as a whole they add up
to a body of data which begins to indicate quite
strongly that not only are sea levels rising, but
they started rising a lot quicker in the mid 20th century.
On the matter of global warming, I stated that
the now famous "hockey stick" curve shows that
temperatures had remained relatively stable for
the 900 years prior to the 20th century. You
replied, " I don't know of many people who claim
that temperature has been constant for the 900
years before 1900. Did the cooling known as the
"Little Ice Age" not happen after all?
Well yes, all the versions of the hockey stick
curve I have seen do show a steady decline in
mean annual temperature for the Northern
hemisphere by about 0.2 degrees from the year
1000 to 1900. The data are very noisy, of
course, but there is general agreement from most
of the various sources from which the
temperatures were garnered. This is the "Little
Ice Age" to which you refer. Actually, the Little
Ice Age was probably only a European/North
Atlantic phenomenon. Data from the rest of the
world are too sparse to know if it was a world
wide temperature drop. But I would contend that a
0.2 degree drop in 900 years is "relatively
stable" compared to a temperature rise of about
0.5 degrees in just the last 100 years.
Given that the world was warmer 1000 years ago
than it is now, sceptics of the global warming
scenario say the present "bump in the graph" is
not an indication of anything unusual going on
and we can all stop worrying. Those on the other
side of the argument answer that the fact that
the world was warmer 1000 years ago, and that we
have had a "Little Ice Age" in between, suggests
that our climate is very sensitive to small
changes in temperature. Large climate variations
due to small temperature changes in the past
imply much greater climate change due to the
temperature spike we have seen in the past 100
years. Just how great that climate change it
going to be is the subject of much speculation at
present. Let us hope that the most pessimistic
forecasts are not well wide of the mark - on the wrong side!
I look forward to planting a vineyard on my 10
acre South facing field up here in Scotland. But
if the world governments are forced out of their
lethargy on global warming and put the breaks on
non-sustainable carbon emissions, I may end up
having to plant rape seed to power my generator!
Geoffrey Kolbe
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
From: Geoffrey Kolbe
Date: 2006 Jul 11, 13:57 -0500
Hello Frank.
Yes, I have seen looked at the link you gave for
the sea level graphs, and in particular at the
Mean Sea Level (MSL) data for "The Battery" in
New York. The website shows a graph of MSL
derived from measurements taken at The Battery
from 1856 up to 1999 (with a break in the
1880's). There is a straight line fit to the data
which shows a mean sea level rise of 2.77mm/year.
By comparison, the MSL trend for Liverpool since 1850 is 1.23mm/year.
Eyeballing data like this to look for trends away
from the linear is not the most ideal method of
analysis, as I am sure you will agree. It is
difficult to see trends less than about one
standard deviation - and this set of data is
pretty noisy. Without deeper and more
sophisticated statistical analysis, I don't think
you are justified in saying, "… there is no
evidence for any upswing at the end of the 20th century."
At the Proudman Oceanographic Laboratory there
are people who spend their time doing just this
sort of statistical analysis and I contacted
Professor Philip Woodworth at the POL to ask him
about higher order trends in the data. He tells
me that it is possible to extract an
"acceleration" of 0.78 +/- 0.3 mm/year/century
for the New York Battery data. For Liverpool
since 1850 it is 0.82 +/- 0.36 mm/year/century -
which is in good agreement. For Amsterdam,
Stockholm, Brest (France) and Sheerness
respectively, the accelerations are 0.42, 0.45,
0.44 and 0.84. And to show the international
nature of these accelerations we can head back to
the United States where San Francisco shows an
acceleration of 1.62 mm/year/century since 1855.
(But the tectonics of the West Coast probably put
a question mark on this number.)
The point is that all these accelerations are of
a very similar order. Each one by themselves
proves nothing, but taken as a whole they add up
to a body of data which begins to indicate quite
strongly that not only are sea levels rising, but
they started rising a lot quicker in the mid 20th century.
On the matter of global warming, I stated that
the now famous "hockey stick" curve shows that
temperatures had remained relatively stable for
the 900 years prior to the 20th century. You
replied, " I don't know of many people who claim
that temperature has been constant for the 900
years before 1900. Did the cooling known as the
"Little Ice Age" not happen after all?
Well yes, all the versions of the hockey stick
curve I have seen do show a steady decline in
mean annual temperature for the Northern
hemisphere by about 0.2 degrees from the year
1000 to 1900. The data are very noisy, of
course, but there is general agreement from most
of the various sources from which the
temperatures were garnered. This is the "Little
Ice Age" to which you refer. Actually, the Little
Ice Age was probably only a European/North
Atlantic phenomenon. Data from the rest of the
world are too sparse to know if it was a world
wide temperature drop. But I would contend that a
0.2 degree drop in 900 years is "relatively
stable" compared to a temperature rise of about
0.5 degrees in just the last 100 years.
Given that the world was warmer 1000 years ago
than it is now, sceptics of the global warming
scenario say the present "bump in the graph" is
not an indication of anything unusual going on
and we can all stop worrying. Those on the other
side of the argument answer that the fact that
the world was warmer 1000 years ago, and that we
have had a "Little Ice Age" in between, suggests
that our climate is very sensitive to small
changes in temperature. Large climate variations
due to small temperature changes in the past
imply much greater climate change due to the
temperature spike we have seen in the past 100
years. Just how great that climate change it
going to be is the subject of much speculation at
present. Let us hope that the most pessimistic
forecasts are not well wide of the mark - on the wrong side!
I look forward to planting a vineyard on my 10
acre South facing field up here in Scotland. But
if the world governments are forced out of their
lethargy on global warming and put the breaks on
non-sustainable carbon emissions, I may end up
having to plant rape seed to power my generator!
Geoffrey Kolbe
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
