Can you really detect a 0.7-inch rise in global sea level?
The media release and abstract are below.
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Media release
Sea-level rise between 2005 and 2011 was predominately caused by the melting of mountain glaciers and polar ice sheets, reports a paper published online this week in Nature Geoscience. The findings suggest that sea level rose by 2.4 mm per year over this period.
Jianli Chen and colleagues used gravity data from the GRACE satellites to estimate changes in ocean mass between 2005 and 2011. They show that the ocean mass increased over this period, resulting in a 1.8 mm rise in sea level per year, largely due to the melting of ice sheets in Greenland and Antarctica, and mountain glaciers. In addition, they assessed changes in ocean density using data from a network of ocean floats. They estimate that a reduction in density over the same period led to a sea-level rise of 0.6 mm per year. Total sea-level rise obtained from these two techniques provides independent support for the estimate of 2.39 mm per year derived from satellite altimeters.
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Abstract
Changes in global mean sea level primarily reflect the sum of a three contributions: water mass changes in the oceans, water density changes, and variations in the volume of the ocean basins. Satellite altimetry data suggest that sea level rose by about2.39±0.48mmyr−1 between 2005 and 2011. However, previous estimates of sea level rise from density and ocean mass changes were lower than the altimeter data indicate. Here
we show that the gap in the sea level budget disappears when we combine gravity data from the GRACE (Gravity Recovery and Climate Experiment) satellite mission and temperature and salinity observations from the Argo programme collected between 2005 and 2011. The Argo data indicate a density- driven sea level rise of 0.60 ± 0.27 mm yr−1 throughout this period. To estimate ocean mass change from the gravity data, we developed a forward modelling technique that reduces the bleeding of terrestrial signals into the ocean data. Our reassessment suggests an ocean mass contribution of 1.80 ± 0.47 mm yr−1 , for a total sea level rise of 2.40 ± 0.54 mm yr−1 , in agreement with the altimeter-based estimates. On the basis of the GRACE data, we conclude that most of the change in ocean mass is caused by the melting of polar ice sheets and mountain glaciers. This contribution of ice melt is larger than previous estimates , but agrees with reports of accelerated ice melt in recent years.
It pays to read the full paper, which is about comparing different measurement systems and trying to account for discrepancies.
ftp://ftp.csr.utexas.edu/pub/ggfc/papers/ngeo1829.pdf
Looks like the ‘climate scientists’ remain consistent in their views on short-term trends. If only ‘skeptics’ would add such caveats to their pronouncements.
Wait, did they attribute the whole rise to just the first 2 components and ignore the third, the volume of the ocean basins? They say the change is 2.4mm (matching satellite altimeters) and then provide a breakdown of 1.8mm for ice melt, and 0.6mm for density. What is the value for the volume change (you know, things like those two pesky little volcanos in Hawaii busy expanding the Big Island ocean-front property. Maybe that’s where all that missing CO2 is hiding!
This is quite a difference from the reports of 3-3.3 mm/yr sea level rise, which is a less scary 9.4″/century than the 12″/century. Also, 2.39 +/- 0.48 mm/hr? I quibble with the decimal places, 2.4 +/- 0.5 mm/yr would be a better expression. Sometimes climate science seems more like my expert freshman chemistry scholars who reported the results of calculations to the number of decimal places those new fangled pocket calculators gave, rather than the significant figures from their measurements.
OK. I’ll agree with the difficultly in the accuracy of any change. But the “caused by the melting of mountain glaciers and polar ice sheets” conclusion?? Really!
That’s an extremely sharp knife to be parsing a hair’s breadth change (literally) in a sea level where ‘level’ has a local variation of several thousand millimeters at any given instant – on a CALM day – by measuring the CHANGE in gravity resulting from a change in the earth’s radius of under a part in a billion
Sea-level rise from a density reduction in the upper ocean, due to warming of the water, only affects (satellite-measured) open-ocean sea-level. It does not affect coastal sea-levels, because it doesn’t affect displacement, which is measured in units of mass, not volume.
Gravity balances mass, not volume, so density changes in the upper ocean cause only in-place vertical movements of the water. That’s why icebergs and sea ice stick up above the rest of the ocean surface, and why their melting or freezing does not affect coastal sea-levels elsewhere.
The same principle applies to density changes in the upper ocean due to warming or cooling of liquid water. Density changes in the upper layer of the ocean cause depth changes equal to a percentage change in the thickness of the affected layer of water. Near the shore, that thickness approaches zero. A small percentage of zero is zero, so temperature changes in the upper ocean do not significantly affect coastal sea-levels.
But only coastal sea-levels matter. Changes of depth in the deep ocean affect nothing of consequence. So it is wrong to headline that estimated 2.4 mm/yr rise for the open ocean. They should be talking about the 1.8 mm/year number.
Unfortunately, Nature Geoscience articles are paywalled, and I can’t find this paper on the web. But my guess is that the 1.8 mm/yr figure also includes Peltier’s estimated 0.3 mm/yr addition to compensate for the hypothesized ongoing post-glacial sinking of the ocean floor. In other words, it’s not real sea-level rise. “Sea-level” means the level of the surface of the sea. Subtracting a model-derived, calculated estimate of one of the factors which is thought to reduce sea-level leaves you with a number that is larger than the actual rate of sea-level rise. 1.8 mm/yr minus 0.3 mm/yr = 1.5 mm/yr ±0.48 mm/yr, a range which nicely straddles the 1.1 to 1.2 mm/yr average rate of sea-level rise measured by the best tide-stations over the last 80 years.
In other words, sea-level is rising at the the same rate that it has been rising for almost a century. The nearly 100 ppm CO2 level increase over that time has caused no measurable increase in the rate of sea-level rise.
What’s more, whether Antarctica is actually gaining or losing ice mass is disputed. Indirect inferences of ice mass from GRACE satellite measurements of the Earth’s gravity field led some researchers to conclude that Antarctica is losing ice mass, but ICESat measurements of ice surface elevation indicate that it is gaining ice mass. Both types of measurements can be confused by land movement, but, in general, the ICESat data is a better indicator.
One thing we know for sure: the net effect of the various contributors to sea level rise has been no increase at all in the rate of sea level rise in response to the last ~3/4 century of rising GHGs. Plus, we know that two other anthropogenic factors, groundwater depletion and decreased reservoir impoundment, should have contributed to an acceleration in sea level rise over that time period, but no such acceleration occurred. So if the contribution to sea level rise from ice sheets is increasing. as some researchers believe, then we know that it is is more than balanced by decreasing contributions to sea level rise from other sources.
Wait a second. NOAA released a report last year that concluded sea level rise from 2005 – 2012 was between 1.2 and 1.6 mm/year. The 1.2 mm/year estimate included 1.0 +/- 0.2 mm/year of mass contribution using the same GRACE data.
Therefore, the GRACE-measured mass contribution to sea level rise from 2005 – 2011/2012 is somewhere between 0.8 mm/year and 2.5 mm/year.
NOAA reported a steric rise of 0.2 +/-0.8 mm/year based on ARGO data. This paper reports 0.6 +/-0.27 mm/year, also based on ARGO data.
Therefore, the ARGO-measured steric component of sea level rise from 2005 – 2011/2012 is somewhere between -0.6 mm/year and +1.0 mm/year.
The total sea level rise from 2005 – 2011/2012 is somewhere between 0.2 mm/year and 3.5 mm/year.
Of course, no climate scientist would *ever* be so duplicitous as to draw any conclusions from such a short data record. We are constantly scolded that 15 or 17 or 20 or even 30 years is not sufficient to draw conclusions from a temperature data set. Right?
Ofcourse not. No way jose. 10 cm would be about doable with any precision i guess using the satellites. Assuming that they don’t drift at all and/or corrections are correctly calculated it still needs some serious massaging of data to get the water signal out of that.
The earth according before
https://dl.dropboxusercontent.com/u/1828618/earthbefore.jpg and after ‘massaging’: https://dl.dropboxusercontent.com/u/1828618/earthafter.jpeg
Some difference.