Real science is never settled.
Sea level rise
is not even settled
within the US government !
The only agreement is that
sea level rose about 400 feet
since peak glaciation
about 20,000 years ago.
Important Question:
How much of the 400 foot
sea level rise
COULD HAVE BEEN
caused by global warming,
assuming man made CO2
is the ONLY cause of
global warming after 1940.
Important Answer:
Only three to six inches,
out of the 400 foot rise,
assuming CO2 is responsible
for ALL the warming since 1940,
when the era of adding
man made CO2 began.
(Note that there is no
scientific proof that CO2
caused ANY of the warming
since 1940)
Tide gages are only suited
to help provide data
for shipping traffic,
on the water depth
at a specific location.
Reason:
Tide gages are located
on moving bases (land).
There is vertical movement
of the land
supporting the tide gage,
that can't be differentiated
from vertical movement
of the sea (sea level rise).
It is typical to have the
sea surface rising a little,
and the land the tide gage
is mounted on,
moving down a little.
That's true for most US
east coast tide gages,
for example.
Tide gages actually measure
local relative sea level
-- the height of the water,
measured along the coast,
relative to a specific point
on land.
The tide gage measurement
includes downward vertical
land movement of an
unknown amount.
Trying to measure
absolute global sea level
with tide gages, is like
measuring the height
of people worldwide,
with every person
standing on a platform
that is moving up or down.
No amount of averaging
would provide a useful answer
for the average height.
I've just described
the problem from using
local tide gages
to estimate an average
absolute global sea level.
Sea level seems like
a simple concept,
but is not.
For one example,
each end of the Panama Canal
has a different sea level !
US Commerce Department's
NOAA says:
“global sea level rise is believed to be
+1.7 +/- 0.3 millimeters per year
during the 20th century”.
But NASA is currently claiming:
"+3.0 +/- 0.4 mm per year.”
Of course I'm assuming
the end of the 20th century
is similar to “currently”.
MEASUREMENT DETAILS
NOAA says that tide gages
measure changes of
local relative sea level
(mostly vertical
land movements).
Tide gages alone
are not suitable
for determining
a global average
of absolute
sea level changes.
But modern tide gages,
used with continuously operating
GPS reference stations
attached to the same structure
the tide gage is attached to,
CAN measure the actual rise
of the surface of the oceans
after subtracting the
vertical land movements.
Downward vertical
land movement
is usually caused
by movement of
Earth’s crust,
compaction of the soil
(landfill is often added
before building
docks and piers,
where tide gages
are located),
and sometimes from
water and oil extraction.
NOAA claims a global absolute
sea level rise of about +1.7 mm/year.
Vertical land movement
along most of the US east coast
is similar, usually less than 5 mm/yr.
NOAA has a “Comparison of
northern Atlantic station trends”
for various ports,
along the US east coast
-- they range from a +1.5 mm/yr.
rise to almost a +6 mm/year rise.
That doesn't mean
the Atlantic Ocean
is rising three times faster
at the Chesapeake Bay Tunnel
(+5.92 mm/year.)
than at Southport, N.C.
(+2.01 mm/year.) !
NOAA states:
"The (tide gage) graphs
give an indication
of the differing rates
of vertical land motion,
given that the absolute
global sea level rise is
believed to be
1.7 +/- 0.3 millimeters / year
during the 20th century."
"These charts ... do not show
how much the surface of the sea
is rising (or falling) --
— they do not show absolute
sea level rise or fall."
"They show relative
sea level trends for
individual tide gage locations,
and taken together,
simply demonstrate visually
the differing rates of
vertical land motion
between the stations."
Tide gages can only be used
to measure local relative sea level,
and its changes.
Comparing one tide gauge to another
only gives us “an indication of the
differing rates of vertical land motion”.
For tide gage data to be useful
for determining actual changes
in absolute sea surface height,
the tide gage must have
an associated Global
Positioning (by) Satellite
(GPS) reference station.
There must be a
continuously operating
GPS reference station
mounted on the same structure
that the tide gauge is mounted on,
so we can precisely determine
vertical land movement (VLM)
of the tide gauge.
(link to my February 24 article on
satellite derived sea level rise
Satellite-derived sea level data
may be useful someday,
but have too many issues now.
NASA uses them because they
show much more sea level rise
than tide gages do -- warmists
almost always select whatever
data show the most sea level rise,
or the most warming -- they ignore
all other data that don't support
their "cause" as much --
data accuracy means
nothing to the warmists !
Satellite altimetry
is a complex calculation
with a dozen or so
“corrections”
and “adjustments”,
all of which are
of a greater magnitude
than the change
in sea surface height !
The NASA data using
satellite data since 1993,
are not really a sea level
measurement.
They are "adjusted" data,
based on a theory.
For one example of tide gages
versus satellites, from 2016:
The Tampa Bay
Climate Science Advisory Panel
(CSAP) concluded that
the Tampa Bay region
may experience sea level rise
between 1 to 7 feet, by 2100.
-- The 1-foot rise
in the next 84 years
was an extrapolation
based on tide gage data.
-- The 7-foot rise
in the next 84 years
was an extrapolation
based on satellite data
since 1993.
One foot to seven feet,
is not a conclusion.
It's wild speculation
on sea level rise
by government bureaucrats
who have no idea
what they are talking about.
NOAA’s long-term
tide gage trend
does NOT radically
accelerate after 1993,
like NASA's
sea level trend does,
by switching to satellite data,
and ignoring tide gage data,
after 1992.
NOAA's tide gage data
are almost perfectly linear.
"Linear" means
no ACCELERATION
of sea level rise after 1940,
the start of the era of adding
man made CO2 to the air.
Acceleration of sea level rise
could be a "signature"
of global warming from
from man made CO2.
Sea level expert
Nils-Axel Mörner
reduces the sea level rise
trend to near zero,
and includes the possibility
of falling sea levels.
Perhaps, in the future,
we'll have adequate
tide gage / global positioning
data to differentiate between
sea level rise and
vertical land movement,
at each tide gage station ?
Perhaps, in the future,
we'll have adequate and
accurate satellite data
to verify the tide gage /
global positioning data,
resulting in the first ever
accurate, and verified,
estimates of absolute
global sea level rise?
But ... please remember that
accurate sea level rise data
can easily be compromised
("fixed with unjustified "adjustments"),
by leftist government bureaucrats,
who want to show more sea level
rise, simply because that is
exactly what they believe in,
and have predicted for decades.
No one wants to be known
for their wrong predictions !