Sea Level Rise, Acceleration, and Closure

Guest essay by Rud Istvan

Background

There is no doubt that interglacials change sea level (SL). And that sea level rise (SLR) can be dramatic on millennial interglacial time scales. That’s what happens when the vast Laurentide ice sheet (among others) melts. But sea level has changed relatively little in the past 7 millennia. We know from archeology that it rose somewhat in the Medieval Warm Period, dropped some during the Little Ice Age, and has been rising slowly since based on tide gauge records. This mostly natural variation is, from 1950-2000, about +1.8mm/year to 2.2mm/year (discrepancy explanation and references follow below). That rate is no cause for alarm. We coped with it for the past century, and can cope with it for the next.

The anthropogenic global warming (AGW) question is whether SLR will accelerate into catastrophic AGW (CAGW) requiring urgent mitigation? Warmunists argue yes, with many alarming images such as National Geographic’s photoshopped Statue of Liberty half submerged (which would require that all of Greenland and Antarctica melts before the next glaciation sets in). We know that in the last interglacial, the Eemian, the sea level highstand was about 6.6 meters above present sea level, so the ice sheets did melt more with global temperature about 2C higher (perhaps 8C higher in Greenland). This took about 3000 years to achieve. That is (660cm/30 centuries) ~22 cm/century, or roughly 2.2mm/year. That rate is no different than the best estimate of present ‘true’ SLR found in what follows.

Consensus Belief

There are two parts to the SLR alarm meme. 1. SLR is accelerating because of AGW. 2. SLR will therefore become a big problem even if not one today. Ergo, future CAGW requires urgent mitigation. Hansen says up to 1 meter SLR by 2060 (and maybe more with tipping), so goodbye Miami Beach. The Obama administration uses occasional recent high tide flooding there to support his climate urgency– without revealing that Miami Beach is 2/3 fill dredged from Biscayne Bay, and is subsiding as the fill compacts and as the underlying Biscayne Aquifer subsides as it is drained to provide Miami’s fresh water.

There are many graphics floating about that support the SLR acceleration alarm.

This seemingly authoritative graphic has been constructed out of two deceptions.

(1) Uses tide gauge records uncorrected for land motion. (C&W 2005 is actually doubly misrepresented: C &W data before 1950 is W,C,&G GRL 2006 [C&W 2005 is only 1950-2000], and there is no 1925-1992 reference period in the 2006 paper). C&W 2005 SLR 1950-2000 was 1.8 mm/year rather than 1.9 and was not accelerating. C&W used approximately 350 long record tide gauges for their ‘accelerating’ reconstruction. There are only 146 PSMSL tide gauges (TGs) within 1000 meters of a differential GPS to correct for vertical land motion of whatever cause, and only about 70 of those are long record TGs. So vertical land motion is NOT excluded in either C&W paper.

(2) Splice on satellite measurements since 1993 that fail the closure test below: observed SLR should roughly equal the sum of observed sea level contributions from thermosteric rise (OHC causes the estimated water column to expand as it warms) plus ocean mass increase (water volume from ice sheet losses).

Side comment: in the SLR literature, there are also two lesser possible SLR contributors: mountain glaciers, and groundwater extraction. Both are sufficiently uncertain and small that they are ignored in this post. There is little doubt that glaciers have been receding most places since 1900, for example in the Himalayas. But IPCC AR4 issued a retraction concerning its alarming conclusion that they would disappear by 2030. Most terrestrial groundwater is annually replenished; else water tables would fall and wells fail. That which is not replenished (e.g. the world’s largest aquifer, the Ogallala) is de minimus in the context of global SLR. (Ice density at 0C is 0.9187, water is 0.9998, so if 365 Gt ice (roughly 365 cubic km) equals 1mm of SLR [reference below] then 1mm of SLR requires adding about 335 cubic kilometers of water. Ogallala withdrawals are about 26-30 cubic km/year and in some places will be exhausted by 2030.)

Tide Gauge SLR

The actual rate of sea level rise is uncertain, let alone possibly detectable AGW acceleration. There are two basic uncertainties.

(1) SLR is inconstant because of multiannual changes in lunar tides (~18 year periodicy) and ocean currents/oscillations (~30-60 year periodicy). Tide gauges show this natural decadal variability almost everywhere. So fluctuations over just a decade or so should be discounted.

(2) SLR is locational because of geographic inhomogeneity. Land does not stand still thanks to plate tectonics, glacial isostatic adjustment (GIA), ground resource extraction (Miami water), and river delta sediment compaction (as in Bangkok). The NH is much better represented than the SH. One paper even said NH SLR is 2.0mm/yr, while SH SLR is only 1.1mm/yr. This peer-reviewed paper would be logically implausible to any 2 year old familiar with bathtubs and water.

SLR fluctuating and land not standing still are both illustrated by Juneau Alaska:

So, what is the ‘true’ tide gauge (TG) measured SLR? There are three ways to estimate this: some big average of a lot of TGs hoping land motions cancel out (the Church and White example above, ~1.8mm/year 1950-2000), model GIA corrected TGs, and direct measurement differential GPS corrected TGs.

There have been a number of papers that have used various subsets and time frames of the ‘stationary’ (GIA or dGPS corrected PSMSL) TGs to infer more reliable estimates of SLR noted by the IPCC. Past half-century estimates range from about 1.7mm/year to about 2.0mm/year, with little to no acceleration. The most relevant recent estimate is Mörner, 2.2mm/year from 1970-2010 during the period when AGW was supposedly happening. This seems plausible, as the average dGPS TG SLR estimates for Western Europe (2.2), the US East Coast (2.1), Japan (2.3), and Australia (2.2) since 1950 are similar. Also proving the sea isn’t truly level, and dGPS isn’t completely accurate.

Satellite Altimetry

As the second chart above illustrated, satellite altimetry tells a very different story, and that story has ‘accelerated’ over time. The present NASA estimate from 1993 to the present is 3.4mm/year (with GIA +0.32). So is the estimate from University of Colorado (with GIA +0.31).

In 2012 it was 3.1mm/year per the second chart above. In 2013 it was 3.2mm/year, as the following chart illustrates.

The ‘acceleration’ arises from Jason-2. But the Jason-2 specification is for instrument stability not exceeding 1mm/year of drift.[1] The acceleration could just be instrument drift. Certainly there has been no causative change in global temperature; Jason-2 is flying during the infamous global warming ‘pause’. Perhaps a comparison to just launched Jason-3 can resolve this; there are already initial discrepancies between the two ‘birds’.

The most recent attempt to reconcile TGs to sat alt to ‘prove’ CAGW acceleration is Jevrejeva et. al.[2] The paper used 1277 PSMSL tide gauges (but explicitly without applying the customary inverted barometer correction—higher air pressure depresses sea level), used a modeled GIA land correction (which dGPS corrected GRACE Antarctic ice loss proved is very unreliable—the paper abstract even said, “Choice of GIA correction is critical…”), to find TG +3.1 versus sat alt +3.2 for the overlap period of 1993-2009 (the sat alt is wrong per both NASA and U. Colorado. Should have been 3.1 mm/year and an exact match, but that might have exposed the manipulated TG data deceits). It also purports to find SLR amplification at both poles, which illogically ignores the hemispheric bathtub problem noted above. It ignores the underlying closure problem entirely. It ignores known decadal tidal variability. The paper isn’t very credible; it seems a desperate warmunist [3] faux defense of the SLR acceleration belief.

Closure

The dGPS tide gauges do not agree with satellite altimetry by a factor of about (3.4/2.2) 1.5x. So which is more correct? SLR should roughly equal the sum of thermosteric rise and ice mass loss. Lets examine those components separately.

Thermosteric rise was estimated to be 1.23mm/year through 2003. Say 1.2. ARGO only estimates are slightly less, perhaps due to known greater uncertainties in the previous XBT sensors. The ARGO period 2005-2010 estimated thermosteric rise is 1.1mm/year (footnote 4).

Greenland’s ice loss depends on which decade, since the 1990’s lost less than the 2000’s. A PNAS estimate for 2003-2009 is 243Gt annually equaling 0.68mm/year. (The NASA conversion factor is 365Gt = 1mm, which would give 0.67.) Other published estimates for multiple years since 2000 range from 0.66 to 0.74. Say 0.7 for closure purposes.

Antarctica is controversial. Perhaps the best estimate is the new dGPS GIA correction to GRACE, which gives 135Gt/year, or 0.37mm/year. Say 0.4.

The sum is 1.2+0.7+0.4 = 2.3mm/year. If ARGO is used, the sum is exactly 2.2. Cazenave’s independently derived estimate from several other references in NCC (paywalled, caption to figure 3) is 2.2. All agree with the dGPS corrected SLR of ~2.2mm/year within uncertainties. There is closure without acceleration.

There is anything but closure with the satellite altimetry. NASA presently says on one web page that present thermosteric rise is 0.8 (wrong), mass gain is 1.8 (wrong), and that SLR is 3.4 (wrong). NASA apparently does not realize that 0.8 + 1.8 = 2.6 ≠ 3.4. NASA climate stuff is seemingly off in a lot of things–temperatures, SLR, ARGO, Antarctic ice loss, closure arithmetic…

There have been three attempts to reconcile satellite SLR to closure and TGs. One set of three similar papers cherry pick short time frames when satellite SLR was less (2.4, 2.5, 2.4 respectively), and throws in higher Antarctic ice loss contributions. [4]^, [5]^, [6] The second argues that satellite altimetry signal processing is wrong (Topex in particular) so the satellite era is really only 2.6mm/year (but accelerating with Jason-2) with closure achieved using higher Antarctic ice loss. The third argues that NASA’s +0.3 GIA is modeled wrong, and according to Peltier’s ICE-5g(VM2) GIA model it should really be -1 with corrected SLR (3.4 -0.3 – 1) 2.1mm/year and closure.[7]

None of these attempts seem very credible.

Conclusions

Tide gauges cannot be relied on for short periods like a decade, or without vertical land motion corrections. Correctly used, they presently estimate about 2.2mm/year with any evidence for acceleration within the uncertainty. That estimate closes with thermosteric rise and ice mass loss for ~2000-2010. The satellite altimetry SLR used to assert SLR acceleration is inconsistent with tide gauge estimates and with closure. SLR acceleration alarm is unjustified.

[1] OSTM/Jason-2 Products Handbook, JPL ref. OSTM-29-1237 (1/20/2009)

[2] Jevrejeva et. al., Trends and Acceleration in global and regional sea levels since 1807, Global and Planetary Change 113: 11-22 (2014)

[3] Warmunist is a term developed and footnoted in essay Climatastrophy in ebook Blowing Smoke. It is an homage to former Czech Republic President Vaclav Klaus’ 2007 book Blue Planet in green Chains, which compares to Lysenkoism.

[4] Chen et. al., Contributions…to recent sea level rise, Nature Geoscience 6: 549-552 (2013).

[5] Li et. al., Assessing the global averaged sea level budget from 2003-2010, Acta Oceanol. Sin. 32: 16-23 (2013)

[6] Willis et. al., Global Sea Level Rise, Oceanography 23: 26-35 (2010)

[7] Peltier, Closure of the budget of global sea level rise, Quaternary Science Reviews (2009), doi:10.1016/j.quascirev.2009.04.004