"Records from tidal stations show a rise on the order of a couple of mm per year, a rate which is little changed over the century or so for which we have adequate records.
But the satellite record shows a rise of 3.3 mm/year.
Why the large difference?
... The two most recent satellites show trends that are significantly larger than the earlier two satellites.
The first two satellites agree quite well, but they both show a much smaller trend than the latter two satellites.
And neither half of the satellite record shows any acceleration.
... we get into the question of the accuracy and precision of the satellite sea level measurements themselves.
These measurements are done by bouncing radar waves off of the ocean surface and measuring how long it takes them to return to the satellite.
Here, repeated measurements are not possible because the sea level at any point changes constantly, and the satellite is rarely in the same position twice.
... The satellites orbit at an altitude of about 830 miles, which is about 1.34 billion millimetres.
So to measure the change in sea level to the nearest tenth of an mm, we’d need to be able to measure the distance from the satellite to the sea surface to a precision greater than one part in thirteen billion … and that is a hard challenge even in a controlled laboratory setting.
Here are some of the difficulties in that measurement.
First is the measurement of the altitude of the satellite itself.
Unless we know that to the nearest mm or so for every second of every day, we’re going to get inaccurate answers.
Next is the varying composition, temperature, cloudiness, and humidity of the atmosphere. All of these change the time it takes the radar signal to return to the satellite.
Then there are the ocean waves, which obviously change the height of the ocean by thousands of mm.
Finally, there is “instrument drift”, the inevitable changes that occur to electronic measuring instruments over time.
Net result?
... according to the University of Colorado one satellite says the sea level is rising at 2.5 mm/year, and a mere 8 days after the end of that satellite’s data (the interval between one satellite and the next in the Colorado sea-level record) the successor satellite says it is rising at 4.1 mm/year
... They’re claiming that in 8 days, the rate of rise jumped by 1.6 mm per year.
Note also that there is absolutely no acceleration in either half of the satellite record, just a step-change between satellites.
Clearly, they’re not able to measure annual sea-level changes to the nearest millimetre, much less to the nearest tenth of a millimetre.
However, the people working on the project are all true believers.
In the same article, Josh Willis is quoted as saying “We know that the oceans are rising because of human-caused interference with the climate.”
... The problem is that starting out with a fixed “scientific” belief like that leads to the people working on the satellite sea-level datasets splicing together what are obviously incompatible satellite results, spreading peanut butter over the cracks so they can’t be seen, and announcing to the world that the satellites show a dangerous acceleration in sea-level rise, so we should all be very worried …
... I’ve said for some time that we shouldn’t put any weight on the satellite results.
However, I have based this solely on the very large differences in both trend and acceleration between the satellite and the tidal station records, and the known difficulties in satellite measurements discussed above.
... But now, at long last, I have the facts to back up my claim.
There’s no evidence of any acceleration in the rate of sea-level rise in either the tide gauge or the shabbily-spliced satellite records.
It’s been going up at on the order of eight inches (200 mm) per century for quite some time, and there’s no sign of any change in that rate of rise."