California:  Rise and Fall – Watts Up With That?

Guest Essay  by Kip Hansen —  23 February 2025 — 1600 words

This is not about California’s nutty politics – but it could have been. 

This is about Vertical Land Motion (VLM hereafter).  VLM is the movement of the surface of the land further from the center of the Earth (up, a rise or uplift) or closer to the center of the Earth (down, a fall or subsidence).

For many locations in North America,  VLM is associated with Glacial Isostatic Rebound.  Basically, as the massive weight of ice on the northern part of northern continents melted away,  that portion of the continental that had been depressed by all that weight, had been rebounding, rising.  At the same time, the southern part of that continental sheet , having been teeter-tottered or bulged upward during the Ice Age, is moving back down.

On the U.S. East coast, the land mass north of Boston, MA , which is approximately the hinge point,  is uplifting and the land mass south of Boston is subsiding.  On the U.S. west coast, parts of Alaska are uplifting and points south are subsiding, from the effects of Glacial Isostatic Rebounding.

Note that all the Relative Sea Level Rise arrows on the California coast are in the “0 to 1 feet per century” range – that is VLM + Absolute Sea Level.  Absolute sea level is understood to be about 1.7 to 2.0 mm/yr – 7 to 8 inches per century.  

When uplift of the coast exceeds slow and steady sea level rise, Relative Sea Level falls.   When coastal  land subsides and absolute sea level rises, the effect is additive, and Relative Sea Level rises faster.  

California has a lot of VLM, both subsidence and uplift,  and some of it pretty extreme.  A recent study, that has measured VLM in California in several different ways, shows this map:

[click here for very hi-res image in new tab/window]

The most obvious feature is the serious major subsidence in the Central Valley – the dark blue blotch that runs diagonally across the state.  The coastal areas are generally neutral and pale blue-ish, indicating either no movement or slightly subsiding.  But, it is important to look at the scales.  There are two scales given. The top scale if for large scale subsidence – darker blues through greens to lighter colors.  This scale is for  +/- 100 to 200 (or greater) mm/year. 

The lower scale is in single digit mm/year, +/- 4.    This lower scale of subsidence, 0 down to -4 mm/yr, is equivalent in magnitude to the rise in absolute sea level. 

And, that is the important point.   The coastal portion of the state of California is generally subsiding at a rate of 1 to 4 millimeters per year.  At the same time, it is generally understood that absolute sea level,  often called  “global sea level”,  is rising at about 2 to 3 mm/yr [when using global tide gauges for the calculation].   In effect then, Relative Sea Level Rise along much of the coast of California can be said to be ‘doubled’ by subsidence.  

To be blunt, the Absolute Sea Level Rise of 2 to 3 mm/yr is not an alarming or dangerous amount. In a century, 100 years, 3 mm/yr comes to 30 cm or 1 foot.  Most areas have already seen that 1 foot of SLR over the previous century without disastrous effects.  To counter-act that 1 foot , those 30 cms, of sea surface rise, a sea wall or dock curbing  16 inches (440 mm) high, made of two standard 8x8x16 inch concrete blocks (in the EU, 215mm x 215mmx440mm) suffices.  

And if we double that amount of Relative Sea Level Rise, say to 6 mm/yr, half of that being subsidence, the total rise comes to 24 inches, 2 feet or 60 cm. 

Now, 2 feet, that’s getting to be something to talk about for locales that have infrastructure built far too close to current sea level or too close to the sea level of the past, which is far more common.   And for locales that have very little altitude above sea level altogether, such as low-lying lands, filled salt marshes turned into sea-level-plus-1-foot neighborhoods of houses with backyard docks on canals and other high-risk areas.  Those low-lying  areas are often spoken of as being “at risk from flooding by sea level rise and storm surge”.  And they are, and they already were, even a century ago.  They are more at risk today and will be even more at risk after another 100 years. 

The reason they are at risk is their relative altitude above sea level.  One foot, two feet, five feet, six feet – the same in meters – it doesn’t matter.  Storm surge can be as high as 14 feet – over 4 meters.   The surface of the sea will reliably rise about one foot – 30 cm – over the next century and to that must be added any local subsidence.

But what they are not at risk from is Climate Change.  The best long-term studies of relative sea levels around the world show that sea level has had a long steady and slow rise since man has been actively measuring it. 

The claims that melting land ice is a major contributor have not been shown to be true.   Water from melting land adds to the absolute sea level rise that is caused by expansion of the sea water due to the gentle warming of the oceans as the world continues to come up and out of the Little Ice Age.   By current rather vague calculations, melting land ice — glaciers, Greenland, Antarctica – may be adding up to 1 mm a year –  few inches, 10 centimeters per century.    The uncertainty stems from the absolute uncertainty of Antarctic ice mass:   is it growing or declining, adding mass or losing mass?  Even NASA, which measures Antarctic Ice Mass is not sure, it has two teams that find totally different answers, both answers derived from the same data sets.

To fight Climate Change the IPCC and the UN (and everyone else on the bandwagon) say we must decarbonize our societies, we must quit adding CO₂   to the atmosphere regardless of cost.  

Combating Climate Change may or may not be a good idea – I don’t think it is – but one thing it will not do is slow or stop sea level rise, not even the fraction of sea level rise actually caused by warming seas.  Reducing CO₂ emissions, atmospheric concentrations of GHGs  or sequestering CO₂ underground or in rocks certainly cannot change the portion of relative sea level rise caused by subsidence. 

Spending tax payer’s money, or society’s wealth, to fight Climate Change will do nothing to prevent today’s or tomorrow’s problems stemming from rising seas.   Those funds must be spent on adaption and mitigation to any negative effects of rising seas. 

Wild and alarming “predictions” of meters of Climate Change-driven sea level rise “by 2025” – in the next 30 years –  are scientifically ludicrous as such a future is literally impossible.  

It is however possible to drive very local Relative Sea Level changes by seemingly impossible amounts through human activities such as  extracting water, pumping water out of aquifers below the surface,  or pumping up  huge volumes of oil, can cause substantial subsidence and conversely, forcing volumes of water or gases (such as in fracking)  down into the Earth under pressure (causing uplift). 

Bottom Lines:

1.  The seas and oceans are rising, have been rising and will continue to rise until the planet again enters a period of cooling, similar to the Little Ice Age or a real full-blown ice age.

2.   Current rates of sea level rise will not be changing much.  If a locality is not currently at risk, it will not be at risk in the future – sea level rise is too slow.

3.  Human infrastructure already at risk will continue to be at risk and that risk will increase in the future – slowly and steadily.  Such localities should spend money and effort on adaption and mitigation.

4.  Vertical Land Motion – up and down – are important factors for localities to consider when looking at risks from relative sea level rise.  Nothing in the fight against Climate Change will effect VLM. Some of the VLM can be mitigated; such as ceasing to extract fresh water or oil close to the sea.  Some of the VLM-caused Relative sea Level Rise must be dealt with by adaptation – raising structures, building seawalls and otherwise protecting infrastructure.

5.  Alarming projections of dangerously high near-future sea level rise are not possible, thus the dissemination of those projections must be seen as politically-motivated Climate Alarm propaganda.

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Author’s Comment:

There is nothing particularly new in this essay, except for the very interesting study on California VLM – look at the Central Valley.  Some of that subsidence may be self-correcting as atmospheric rivers bring lots of new water to recharge the underlying aquifers.  But those aquifers have been being pumped out at tremendous rates to irrigate fields, orchards and vineyards for a long time. 

But, in general, coastal California has little to worry about – most seafront areas are backed by bluffs, huge remnant sand dunes in some places like Manhattan Beach, that rise rapidly, like most of Los Angeles.

There are areas around the edges of San Francisco Bay that are just filled wetlands right at sea level and then you have the Sacramento River Delta.  The surface of the Sacramento River at Washington Lake in Sacramento, 87 miles across the Bay and upstream,  is only 6 feet above San Francisco Bay.  They are potentially in trouble now. 

Rising Sea Level scares are just that – scares.  It is far past time to begin to adapt and mitigate. 

Thanks for reading.

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