Arguments
Madness over sea level rise in North Carolina
Posted on 29 June 2012 by John Bruno
Sleepy North Carolina became an international topic of conversation (and ridicule) this month thanks to our state legislature's bills declaring sea level rise "illegal", or more accurately, insisting that state planning for future sea level be based only on "historical records", meaning tide gage measurments during the last century (translation; there is no acceleration of sea level rise here folks - now move along).
What does the science say?
Everything started with the publication of the North Carolina Sea-Level Rise Assessment Report, prepared by the N.C. Coastal Resources Commission’s Science Panel on Coastal Hazards in March 2010. The panel included regional and international experts on sea level rise and coastal geophysics from many of the state’s most esteemed scientific institutions, including UNC-CH’s Institute of Marine Sciences, UNCW, NC State, the US Army Corps of Engineers, East Carolina University, and Western Carolina University. (read more about the charge given to the panel by the state here)
Past sea level rise: The report describes the empiral findings of several studies of past sea level rise in North Carolina (Horton et al. 2009, Kemp et al. 2009, Zervas 2004, see references here). In the 20th century, sea level rise increased from 1mm/year to about 3.2 mm/year (12.6 inches/century). Eight tide gage stations indicate the recent sea level rise has varied from ~ 2mm/year in the southern part of the state to nearly twice that rate in the north, e.g., 4.3 mm/year or 17 inches/century in Duck, near the Virginia border (see Table 1). (Note a recently widely discussed paper on NC sea level rise (Kemp et al 2011) was not included in the report since it was not publsihed when the panel met in 2009 and 2010, however, most of the data/findings in Kemp et al 2011 were included as they had been publsihed in earlier related outlets, including Kemp's 2009 PhD dissertation.)
The NC science panel's report is supported by a just published paper in Nature Climate Change (Sallenger et al 2012), that describes a global hot spot of sea level rise that begins at Cape Hatteras, NC. Between 1970 and 2009, average sea level rise in the hot spot (which includes Washington, New York City, and Boston) was 3.80 mm/yr (±1.06). The authors tentatively attributed the hot spot to another aspect of global warming; the expected slowdown of the Atlantic Meridional Overturning Current, although see a discussion of other potential explanations here.
Sea level rise measured with tide gauges for 60-yr time series at locations across North America. source Circles are colour-coded to reflect computed SLRDs; no colour fill indicates SLRDs that are not statistically different from zero. Confidence limits are ±1σ and account for serial correlation; 50- and 40-yr time series results are shown in Supplementary Fig. S3.
Future sea level rise: Next, as requested, the panel cautiously projected some of the possible scenarios of future sea level based on different degrees of sea level rise acceleration. Globally, sea level rise is known to be accelerating (also see here) and expected to accelerate further due to greenhouse gas emissions and global warming, and more directly to the loss of ice mass from Greenland and Antarctica.
..based on multiple indicators suggesting that global climate is warming, the Panel believes that an acceleration in the rate of SLR is likely.
Confidence levels and margins of error are not calculated for the individual rate curves because the curves are considered to be the upper and lower boundaries of sea level over the next 90 years. It is important to understand that the curves were generated using a constant acceleration rate to reach the selected endpoints derived from the literature, and are not projections of actual sea level at specific future dates. As a consequence, it is not accurate to interpolate quantities of sea level rise for specific years since we do not know whether RSL acceleration will be constant over the next 90 years. The curves are primarily intended to illustrate the expectation of increased acceleration.
The Science Panel does not believe, based on the data available at this time, that it is appropriate to attempt to quantify confidence intervals or margins of error beyond those inherent in the chosen scenarios, as informed by the published literature. Nevertheless, the Science Panel is confident that the curves presented constrain the plausible range of sea level by 2100 as accurately as is possible at this time.
The panel's projections were based on the current science about sea level rise and climate change and are very much in line with the broad and deep consensus within the scientific community. The panel did not argue that any of the scenarios were more or less likely than others; they simply reported the probable range of sea level rise by 2100. They did not rule out lower sea level rise or far higher sea level rise, both of which are possible. Finally, the panels sea level rise forecast for North Carolina is concordant with what has been forecasted globally.
Enter the politics
The report immediately attracted the attention of real estate investors and coastal development lobbying groups like "NC 20" that responded with anti-science propaganda like this (PDF). These groups successfully lobbied the state legislature to declare that coastal communities should only prepare for sea level rise this century of eight inches, which is lower than the rate most of North Carolina is already experiencing.
Thankfully, sanity and science prevailed (for the momemt) when last week, the NC house of representatives voted 144 to 0 against the Senate bill "outlawing" accelerated sea level rise. This is a radical change of heart by a house that only the week before had voted in favor an even more anti-science bill.
This battle surely isn't over. But there are already several of lessons that could apply to similar battles going on in other states in the US and also in Australia. The most striking is how easily a small handful of advocates for junk sea level rise science were able to persuade the state legislature to write and initially vote in favor of a pretty crazy bill. They spout the same denier swill that SkS has been debunking for years. And they threw in some unique arguments for good measure, e.g.:
Moreover, although thermal expansion does cause satellite-measured mid-ocean sea level to rise, it does not necessarily cause coastal sea level to rise. If deep-ocean water were to expand, it would, indeed, affect coastal sea levels. But when surface water warms, it rises in place, like ice, and its displacement is unaffected, so it does not affect coastal sea levels.
The second lesson for me was how effectlve the widespred public shaming of the legislature and the debunking of NC20's propaganda was in changes votes (if not changing minds).
Note: for more information on North Carolina coastal sea level rise, see John Bruno's SeaMonster blog.
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The longer-term problem is that ice mass loss from the Greenland & Antarctic Ice Sheets is accelerating and this, coupled with the Earth's current energy imbalance (that dictates further warming is effectively dialed in), suggests an acceleration of sea level rise is likely at some point in the future. This will be influenced by how the trend in human-made and natural volcanic reflective aerosols develop too.
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This is why evaluations of sea level change need to take GIA into account, and use measurements from widely spread tidal gauges and satellites. Otherwise you may get thrown off by local effects.
To make things even more interesting, a significant change in mass at the Earth's poles will slightly change the Earth's rotation, which in turn effects ocean currents, tending to pile water higher on east coasts than west coasts (in the case of the loss of the WAIS). (discussion here)
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