On Sea Level Rise

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Sea levels are rising with increasing global temperatures. It seems that whenever there is a new estimate of the rate of melting of one or more major parts of the polar ice caps, that estimate is higher than previously thought. By the end of the century, the most aggressive estimates suggest that we will have close to 2 meters (6 feet) of sea level rise along the coasts.

So,here are three sea level rise items for you.

First, the Obama Administration will begin to plan for sea level rise in all major federal projects to which this variable pertains. See this item in the Washington Post.

The order represents a major shift for the federal government: while the Federal Emergency Management Administration published a memo three years ago saying it would take global warming into account when preparing for more severe storms, most agencies continue to rely on historic data rather than future projections for building projects.

The new standard gives agencies three options for establishing the flood elevation and hazard area they use in siting, design and construction of federal projects. They can use data and methods “informed by best-available, actionable climate science”; build two feet above the 100-year flood elevation for standard projects and three feet above for critical buildings such as hospitals and evacuation centers; or build to the 500-year flood elevation.

Second, not breaking news but something you may want to know about, is the US Army Corps of Engineers report on risk management for coastal communities, here.

Third: you may remember a while back I made a map that showed North American coast lines under the extreme scenario where all of the polar ice on Earth melts. That would represent about 80 meters of sea level rise. Well, the data I used to do that, from the USGS, had a problem, and with new data I’ve redone the map (and focused on the eastern part of the continent because it is more interesting). See: How high can the sea level rise if all the glacial ice melted?

That is all, thank you very much.

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19 thoughts on “On Sea Level Rise

  1. Sorry but you are wrong!!
    There is no rise in sea level because N.Carolina passed a law saying there is no rise in sea level, so there can’t be any raise as the sea would be in violation of NC law!!!!

  2. Boats will have a hard time negotiating the steep cliff in the ocean between the waters of North Carolina and the rest of the ocean.

  3. Sure, but technology and entrepreneurial spirit will soon create a set of water “ramps” to allow safe (and Fun!) passage of important commercial shipments between NC waters and other realms. Or will it be hoverboards? There’s no way to tell.

  4. That steep permawave on the boundaries of NC waters will be a Mecca for surfers the world over! I imagine the local chamber of commerce will soon fund a surf NC add campaign.

    Now, if we could tap the permawave for energy production, then we’d have a real continuous motion machine worthy of a Nobel!

  5. Well AR4 said ~64 meters (Table 4.1) and AR5 said ~66 meters (again Table 4.1).

    So, I’m sort of thinking the USGS data might be somewhat dated, it’s hard to tell, but most of the underlying references seem to date to the 1990’s.

    Also the NOAA-USGS-FEMA-USACE work fairly close together where their mission statements overlap.

    The USACE is the permitting body for anything done in the coastal zone, as such (or vica versa), the federal coastal zone management lies primarily within the USACE mission statement.

    So while NOAA (sea level, tide and offshore wave data), FEMA (flood plain mapmakers) and USGS (geology) have their roles, the people who integrate that data are mostly within the USACE (e. g. FEMA currently contracts heavily to USACE for water levels within a probabilistic framework, this work is ongoing).

    What all they do at the state level (NC and VA) is pretty much a real estate joke.

    1. Different approaches have led to different numbers. If you look at the map I refer to the problem is course enough that it does not matter for the reasons stated. I have no reason to believe one estimate is much better than the other. The IPCC uses some more recent estimates, but some of those estiamtes consider only part of the ice sheets, where the USGS is trying to count all of the ice. At some point in the future if a review comes out that is convincingly more useful I may once again redo the map.

  6. AR5 references for GIS and AIS:

    Bamber, J. L., et al., 2013: A new bed elevation dataset for Greenland. Cryosphere, 7, 499–510.

    “We estimate that the volume of ice included in our land-ice mask would raise mean sea level by 7.36 m, excluding any solid earth effects that would take place during ice sheet decay.”

    The “solid earth effects” would be due to considerations of a dynamic geoid (e. g. Jerry Mitrovica).

    Fretwell, P. T., et al., 2013: Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. Cryosphere, 7, 375–393.

    “The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, …” (from Table 8 the actual SLE is 58.3 meters)

    Seeing as no author on any of those two papers is directly affiliated with the USGS, and in the list of IPCC authors (only three are listed from the USGS, and that of those three none appear in Chapter 4 of AR5 WG1, methinks I’ll WILL contact the USGS in regards to this matter (and CC: a few authors on that Chapter 4 list that are from the USA).

    Thank you very much.


  7. You don’t even know if it’s 64 meters or 66 meters? Uncertainty! You must not know anything at all! The sea might even retract for all you know! I say we start building underwater right now for the inevitable retraction of the sea and opening of new oceanfront property!


  8. Actually, we don’t know if it is 60, 64, or 80!

    (But, as I said, the coarseness with which the map is made is so great, combined with the uncertainty as to where the strand line would erode to, makes it almost moot unless one does a really detailed geophysical study.)

  9. Greg,

    I have just emailed the appropriate list of people at the USGS, IPCC lead authors (USA) and the corresponding authors of the two peer reviewed papers as cited above.

    Hopefully, this matter will be addressed by the appropriate individuals/bodies in regards to this matter.

    Thank you very much.

    Very Respectfully,
    Everett F Sargent

  10. Everett, I want to say it again because your letter (thanks for the cc by the way) indicates that you did not understand when I said it before.

    The difference between the two estimates (and that difference is too large to be OK, we need to get the numbers right) does not affect the outcome of my map, given the very coarse divisions used in the original USGS map that I based it on. In fact, 64 meters is what I used as the cutoff because it was closest to the 80 m estimate, to provide a very conservative estimate of a fully inundated coast line. The upper elevation, which defines the upper end of the “gray zone” (shaded in gray!) is much higher than the 80 meter USGS estimate (114 meters). The purpose of the grey zone is to define the region in which a more careful and local look would be required to actually place the strand line if ALL of the ice melted. This needs to be a large area because of several factors. First, sea level does not rise uniformly. Second, gravitational effects would increase sea level beyond a simple estimate of water volume. Third, there might be in some places, isostatic effects that increase effective sea level rise. Fourth, and probably most important, transgression will eventually cut the strand line horizontally horizontally a great distance, such as on glacial moraines (i.e., Long Island) where eventually the non-bedrock sediment will be eroded away no matter what the elevation.

    But thank you for writing the letter to the USGS. It would be nice to have numbers in which we have more confidence.

  11. Greg,

    Yes, I needed to keep you in the loop, as it were, as it’s the only respectable thing to do.

    (4) The “grey zone” at least for the CONUS would mostly affect the areas of relatively low relief which have large unconsolidated sedimentary deposits, primarily the east and gulf coasts (and similarly globally).

    I’m currently using hypsometry data (one minute resolution) from NOAA:


    The Excel file is in aggregate horizontal depth bins (and one needs to perform a vertical integral instead of a horizontal integral to see the volume versus ocean depth relationship).

    Anyways, the hypsometry above current RSL appears to be significantly flatter than that below RSL (at least visually from the NOAA graphic).

    One can make a 1st order SWAG using the current hypsometry raised so many meters (worth a try).

    (1) & (2) Yes, the dynamic geoid (solid earth) work I mentioned above suggests that CONUS could see ~1.4 the SLE for WAIS and GrIS (five meters of SLE). Tides will change as well as steric effects.

    (3) Long term GIA (pitch & heave DOF’s) would occur in those areas that lose their ice sheets.

    So yes, the subject is rather complex and perhaps beyond our current understanding to some degree.

    However, these calculations are meant to be ‘dumbass’ simple, in terms of global sea level equivalent, and as such the 1st metric will always be a rather simple ‘what melts here will end up here’ in a uniform global sense.

    That is all.

  12. Thank you, Michael 2, for informing us that if the ground is not uniformly flat, then any deviation in height must be concentrated in one big mound. I wonder if cars & buses will go over it or around it?

  13. Michael, you’ll find relative sea level going down lots of places like Oregon and elsewhere on the Ring of Fire. That is mainly the land going up.

  14. Re. uneven sea level rise:
    Chris Mooney had an article about the long-term effect of West Antarctic melting on the US. The melting will cause a decrease in Antarctic gravity with the result that water will move away from Antarctica and towards the US.

    “West Antarctica is so large that it pulls the global ocean toward it, which slopes upward toward the ice sheet and the Antarctic continent in general. But if West Antarctica were to lose a substantial part of its ice, then the gravitational pull would relax, and sea level would actually decrease near the ice sheet even as it spreads and increases across the global ocean.
    But not evenly. Instead, areas farther from West Antarctica would get more sea level rise, and North America and the United States might get more than any other inhabited place on Earth.”
    http://www.washingtonpost.com/news/energy-environment/wp/2015/01/22/the-u-s- has-contributed-more-to-global-warming-than-any-other-country-heres-how-the- earth-will-get-its-revenge/

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