Oh say can you see modern sea level rise from a geological perspective?

Adaptation: “It’s déjà vu, all over again!”If mankind and our infrastructure adapted to this…

Figure 2. Northern Hemisphere temperature, atmospheric CO2 and sea level since 1700 AD.

We can adapt to this without breaking a sweat…

Figure 3. Projected sea level rise through 2100 AD.

Particularly since sea level rose just as fast from 1931-1960 as it has risen since 1985…

Figure 4. Paracyclical sea level rise since 1931.

Anyone threatened by 6-12 inches of sea level rise over the next 85 years is already being flooded by high tides and/or storm surges. The red areas on this EPA map would be threatened by 1.5 meters of sea level rise.

Figure 5. Coastal areas threatened by 1.5 meters of sea level rise along US Gulf Coast (US EPA).

Bear in mind the fact that it would take an average rate of sea level rise nearly twice that of the Holocene Transgression for sea level to rise more than 1.5 meters (~5 feet) over the remainder of this century. This caused sea level.to rise by ~10 mm/yr for about10,000 years…

Figure 6. Animatiion of Late Pleistocene to Early Holocene deglaciation (Illinois State Museum).

Approximately 52 million cubic kilometers of ice melted during that 10,000 year period.

52,000,000 km^3 ÷ 10,000 yr = 5,200 km^3/yr

The Antarctic and Greenland ice sheets were recently estimated to be losing ~213 gigatonnes of ice mass per year (Shepherd et al., 2012).. This is equivalent to 213 km^3/yr.

5,200 km^3/yr ÷ 213 km^3/yr = 24

Polar ice sheets are currently melting at about 1/24th the rate of the Holocene Transgression, if they are actually melting.

Isostacy, Eustacy, Cycles, Supercycles, Paracycles and Sequence Stratigraphy

Some have disagreed with the use of the words “cycle” and “oscillation” as they pertain to climate change and sea level. From a purely mathematical standpoint they are correct. Climate and sea level cycles and oscillations are technically quasi-periodic fluctuations. However, cycle and oscillation have become the accepted nomenclature for a wide range of quasi-periodic fluctuations and they are easier words to type.

Firstly, a couple of definitions:

Isostacy: 1. n. [Geology] The state of gravitational equilibrium between the lithosphere and the asthenosphere of the Earth such that lithospheric plates “float” at a given elevation depending on their thickness. The balance between the elevation of the lithospheric plates and the asthenosphere is achieved by the flowage of the denser asthenosphere. Various hypotheses about isostasy take into account density (Pratt hypothesis), thickness (Airy hypothesis), and pressure variations to explain topographic variations among lithospheric plates. The current model consists of several layers of different density. See: asthenosphere, eustasy, isostatic, isostatic correction, lithosphere, plate tectonics, topographic map

Eustacy: 1. n. [Geology] Global sea level variations. Changes in sea level can result from movement of tectonic plates altering the volume of ocean basins, or when changes in climate affect the volume of water stored in glaciers and in polar icecaps. Eustasy affects positions of shorelines and processes of sedimentation, so interpretation of eustasy is an important aspect of sequence stratigraphy. See: accommodation, basin, hiatus, isostasy, Milankovitch cycles, plate tectonics, regression, sequence stratigraphy, systems tract, transgression

Simply put… Isostasy is the land moving up and down; while eustasy is the water moving up and down. Sequence stratigraphy is the process of identifying depositional sequences as they relate to the cyclical rise and fall of sea level.

Figure 7. Cycles, paracyles and supercycles (AAPG).

For a detailed explanation of “relative changes of sea level from coastal onlap” see the following…

C.E. Clayton, ed., Seismic stratigraphy – applications to hydrocarbon exploration: Tulsa, Oklahoma, American Association of Petroleum Geologists Memoir 26, p. 49-212.

Or you can check out the University of Georgia’s online guide to sequence stratigraphy.

The Holocene Highstand

There are at least two schools of thought regarding Holocene sea level changes. The view favored by the IPCC and the so-called scientific consensus is that of a rapid rise in sea level during the early Holocene followed by a static quiescence from about 6,000 years ago up until the dawn of the “Anthropocene” (generally the Industrial Revolution). The second school of thought, favored by many (if not most) sedimentary geologists, is that of a dynamic Holocene sea level and a pronounced Holocene Highstand.

Figure 8. Sea level was 1-2 meters higher than it currently is during the Holocene Highstand.

Evidence for a Holocene Highstand is global in nature, consisting of stranded beaches and other facies associated with shorelines 1-2 meters higher than present day from 4-7 kya.

Amazing GRACE

Greenland is alleged to have lost between 93 and 191 gigatonnes of ice per year from 1992 (ten years before GRACE was launched) and 2011. If we assume 1 Gt of ice = 1 km^3 of ice and that the current volume of the Greenland ice sheet is ~5 million km^3 and that Greenland continues to melt at a rate of 142 km^3/yr over the next 90 years… The Greenalnd ice sheet will lose a bit more than 0.3% of its ice volume. ~142 Gt of ice per year equates to about 0.003% of ice mass loss per year. At 142 Gt/yr, Greenland will be ice-free in 35,211 years.

GRACE (Gravity Recovery And Climate Experiment) consists of two satellites, launched in 2002, that measure subtle variations in Earth’s gravitational field. GRACE is the ideal tool for measuring changes in Earth’s polar ice caps.

Figure 9. GRACE Mission (Source University of Texas).

One of the most prolific authors on GRACE has been Dr. Isabella Velicogna, UC Irvine (one of Sheppard’s co-authors). Back in 2009 Dr. Velicogna published this paper in GRL:

Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE.

Dr. Velicogna concluded that the ice mass-loss was “accelerating with time.” She found that “in Antarctica the mass loss increased from 104 Gt/yr in 2002–2006 to 246 Gt/yr in 2006–2009.”

Figure 10. Total Mass Difference: TMD = Actual GRACE measurements. TMD – IJ05 and TMD – ICE5G = GRACE measurements adjusted for GIA (Riva et al., 2007).

Furthermore, the GIA-adjusted Total Mass Differences (TMD) from the TU Delft publication are significantly lower than those of Velicogna 2009. GIA is the abbreviation for “glacial isostatic adjustment,” sometimes referred to as post-glacial rebound (PGR). The areas of the Earth’s crust that were covered by thick ice sheets during the last glacial maximum were depressed by the ice mass. As the ice sheets have retreated over the last 15-20,000 years, the crust has rebounded (risen) in those areas. So, the GRACE measurements have to be adjusted for GIA. The problem is that no one really knows what the GIA rate actually is. This is particularly true for Antarctica. Riva et al., 2007 concluded that the ice mass-loss rate in Antarctica from 2002-2007 could have been anywhere from zero-point-zero Gt/yr up to 120 Gt/yr. Dr. Riva recently co-authored a paper in GRL (Thomas et al., 2011) which concluded that GPS observations suggest “that modeled or empirical GIA uplift signals are often over-estimated” and that “the spatial pattern of secular ice mass change derived from Gravity Recovery and Climate Experiment (GRACE) data and GIA models may be unreliable, and that several recent secular Antarctic ice mass loss estimates are systematically biased, mainly too high.”  So, there’s no evidence that the Antarctic ice sheets have experienced any significant ice mass-loss since GRACE has been flying.

The GIA has generally been as large or larger than the asserted ice mass-loss. In 2009, Velicogna asserted that Antarctic ice mass loss “increased from 104 Gt/yr in 2002–2006 to 246 Gt/yr in 2006-2009.” In the current paper, supposedly showing accelerated melting, they claim that Antarctica is lost an average of 71 Gt/yr from 1992-2011. Both of those estimates add up to about 1,400 Gt from 1992-2011. This would mean that Antartica didn’t lose any ice before 2002 or after 2009. The steepening of the trend occurred in mid-2006. So there were 5.5 years of +72 Gt/yr and 3.5 years of -70 Gt/yr measurements. Velicogna didn’t repeat the mistake she made in 2006, when she actually published the pre-GIA (PGR) measurements…

Figure 11. Antarctic ice mass from GRACE. The blue curve is prior to GIA/PGA adjustment (Velicogna and Wahr, 2006)

Before the GIA adjustment, GRACE indicated a gain in ice mass. This means that from 2002-2006, GRACE was measuring a mass gain of 72 ±76 Gt/yr. Note: the error bar of the GIA is larger than the measured anomaly. From 2006 to 2009, GRACE recorded a net loss of 70 ±76 Gt/yr. Now, there should be some PGR or GIA. However, prior to Thomas et al., 2011 PGR/GIA had been model-derived. Now it appears that PGR/GIA is actually much smaller than the models indicated and its distribution is highly variable.

But… Let’s assume that the Velicogna GIA/PGR adjustment is correct anid ice mass loss did accelerate from 2002-2009. Where did the water go? The rate of sea level rise has decelerated since 2002. Where did all that meltwater go?

Figure 12. Decelleration of sea level rise during global warming hiatus.

More fun with numbers… Let’s assume that Antarctica is losing 190 Gt of ice mass per year. 190 Gt sounds like a really big number, doesn’t it? 360 Gt of ice melt will yield 1 mm of sea level rise. 190 Gt is good for ~0.5 mm/yr of sea level rise. The volume of ice in the Antarctic ice cap is ~30,000,000 km3. 190 Gt is roughly 0.0006% of 30 million km3. GRACE is measuring no net change in the ice mass; yet a 0.0006% annual change is being calculated from the PGR adjustment. At 0.0006% per year, Antarctica will have lost 0.06% of its ice mass by the end of this century (99.94% of Antarctica will not have melted)! And sea level will have risen by… (drum roll)… 46 millimeters!!!…{ SARC} Almost 2 inches!!! Very extreme!!! {/SARC}

A recent geoid-corrected sea level estimate using GRACE measurements (Baur et al., 2013) indicates that the actual seal level rise is about half of what Jason/Topex indicate. The GRACE value agrees with another recent and equally unpublicized NOAA study of tide gauge data.

Is Sea Level Really Rising?

In light of Baur et al., 2013, this is a fair question. I think it probably is rising, barely rising. Two of the primary sub-tectonic components of sea level change are 1) thermal expansion of seawater and 2) glacial retreat (negative mass balance, ice ablating faster than accumulating). Thermal expansion only occurs when the climate is warming.

There has been little to no net thermal expansion since the most recent phase of warming stopped. Glacial retreat will generally occur whenever the climate isn’t significantly cooling. The most recent period of significant glacial advance (positive mass balance, ice accumulating faster than melting/ablating) was during the Little Ice Age. Most alpine/valley glaciers, like Glacier National Park, reached their maximum Holocene extent during this period. Most glaciers will remain in a state of negative mass balance until the climate begins to cool on a similar scale as the Little Ice Age. This is why the average rate of sea level rise dropped from 3.6 mm/yr to ~2.7 mm/yr since 2003. However, many other factors affect sea level, it’s not rising everywhere and the rate is extremely variable locally and regionally.

However, Mörner, 2003 makes a very strong case that the adjustments applied to the raw TOPEX/POSEIDEN data actually account for all of the apparent sea level rise from October 1992 through April 2000.

Global mean sea level may be eustatically rising at a rate of ~3 mm/yr… It might be rising at half that rate or not at all. It’s definitively not rising at an alarming rate.

Oh Say Can You See… Modern Sea Level Fluctuations From a Geological Perspective?