We'll start with Burton's spiel:
Brest, France is not a proxy for global sea levels.
Pete wrote, "Brest, France is not a proxy for global sea levels.”
It's not a proxy at all. It's actual, measured sea-level, the longest such measurement record in the world. It goes way back to 1807.
I mentioned that the NOAA graph of sea-level at Brest, France looks very linear for more than a century. But what seemed obvious to me apparently wasn't obvious to DavidAppell, because he asked I "prove it with mathematics." So, I did.
He hasn't even replied. A "thank you" would have been nice.
FYI - 3.0 ± 0.7 mm/year between 1993 and 2010
Probabilistic reanalysis of twentieth-century sea-level rise
"Our analysis, which combines tide gauge records with physics-based and model-derived geometries of the various contributing signals, also indicates that GMSL rose at a rate of 3.0 ± 0.7 millimetres per year between 1993 and 2010, consistent with prior estimates from tide gauge records4. The increase in rate relative to the 1901–90 trend is accordingly larger than previously thought; this revision may affect some projections11 of future sea-level rise."
Global Mean Sea Level (GMSL) rise
William V. Sweet and John J. Marra | June 8, 2016
National Oceanic and Atmospheric Administration’s Center for Operational Oceanographic Products and Services and National Centers for Environmental Information
High tide flooding, measured locally by National Oceanic and Atmospheric Administration (NOAA) tide gauges, is described as “nuisance”, “sunny-day” and “recurrent”. Such minor flooding is increasingly common with little or no storm effects (Sweet et al., 2014). Impacts include degraded storm water systems, infiltration into waste-water systems, contamination of fresh water supplies and salt-water flooding of roads, homes and businesses; tidal flooding is disrupting commerce and ways of life.
During 2015, there was extensive reporting of tidal flooding impacting cites in New Jersey, Delaware, Maryland, Virginia, North and South Carolina, Georgia, Florida, Louisiana, Texas and California to name a few.
Tidal flooding is increasing in frequency within U.S. coastal communities due to sea level rise (SLR) from climate change and local land subsidence. Tidal flooding is further exacerbated by climate variability of the El Niño Southern Oscillation (ENSO). Decades ago powerful storms caused such impacts, but due to SLR, more common events are now more impactful. Event frequencies are increasing rapidly – two to three times or more frequent than just 20 years ago (Table 1).
Annual tidal flood rates have entered a sustained acceleration phase at many locations (Sweet and Park, 2014) as the annual distribution of daily highest tides steadily surpasses “fixed” elevations. Thus, once flooding becomes problematic, impacts will become chronic rather quickly and communities should plan for this eventuality.
This document updates the number of days during the May 2015 – April 2016 (2015) meteorological year with a nuisance tidal flood. Nuisance flooding is defined as a water level measured by NOAA tide gauges (tidesandcurrents.noaa.gov) above the local NOAA National Weather Service (NWS) threshold for minor impacts (water.weather.gov/ahps) established for emergency preparedness (Figure 1a).
We highlight the 27 long-term gauges across the U.S. examined by Sweet and Park (2014) and an additional gauge in Virginia Key (Miami region) because of the extent of tidal flooding that occurred there in 2015.
2015 Conditions. During 2015, anomalously high (>0.1 m) coastal sea levels persisted (Figure 1b) along the U.S. Southeast and Gulf Coast and parts of the West Coast. This increased the reach of typical storm surges and high tides. In response, the frequency of nuisance tidal flooding in 2015 increased by more than 50% on average across all locations as compared to 2014 (Figure 1c).
During 2015, several locations experienced all-time records (see Table 1), including Wilmington (90 days), Charleston (38 days), Port Isabel (36 days), Mayport (19 days), Virginia Key (Miami region) (18 days), Key West (14 days) and Fernandina Beach (7 days). Frequencies were at or above the 1950-2013 trend expected values for 2015 at most locations. It is important to note that the overall number of daily exceedances per year is correlated to the height of the local NWS threshold. Where the thresholds are low, more flooding occurs (e.g., Wilmington); where thresholds are highest such as in St. Petersburg and Galveston (reflecting hurricane flood mitigation structures), little to no exceedances were recorded.
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The National Oceanic and Atmospheric Administration (NOAA) water level (tide) gauges have been measuring water levels around the U.S. for over a century, providing clear evidence of sea level rise relative to land (SLR) around most of the continental United States and Hawaii. As SLR increases mean sea level (MSL), there is naturally an increase in tidal datum elevations, which are typically used to delineate inundation thresholds. Direct consequences of rising sea level against fixed elevations such as today’s built infrastructure also include increased inundation during extreme events both spatially and temporally. Not only are extreme flooding events reaching higher grounds and covering larger areas due to SLRrel, the frequency and duration of these extreme flood events are increasing.
Another consequence of SLRrel is the increase in lesser extremes such as occasional minor coastal flooding experienced during high tide. These events are becoming more noticeable and widespread along many U.S. coastal regions and are today becoming more of a nuisance. As sea levels continue to rise and with an anticipated acceleration in the rate of rise from ocean warming and land-ice melt, concern exists as to when more substantive impacts from tidal flooding of greater frequency and duration will regularly occur. Information quantifying these occurrences to inform mitigation and adaptation efforts and decision makers is not widely available.
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