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Marin IJ
Marin does not face 4.9 feet in sea level rise by 2050. It faces 7 feet King tides now
On October 29, the Marin IJ published a cover page article on the subject: Marin IJ article.
Within this article, Dana Brechwald from the Bay Conservation and Development Commission (BCDC) stated that Marin faces a 4.9 feet in sea level rise by 2050. A rise of 4.9 feet in just 27 years from now seemed absurd. So, I looked into it.
(Please click on the images to enlarge them)
First, a short introduction to sea level rise
Let's go back to 1900 to look at a long-term time series.
Between 1900 and 2018, sea level rose by 205 millimeters or 8 inches. The rising rate over the entire period is 1.7 millimeters per year. Since around 1990 or so, this rising rate has accelerated. So, let's look at this recent period.
The above graph shows that from 1993 until 2022 sea level rose by 100 millimeters or 3.9 inches or 3.4 millimeters per year. The above graph shows a linear trend. Thus, we could project that by 2050, sea level would rise by:
3.4 mm x 27 years = 92 mm or 3.6 inches
The above forecast may potentially be on the high side given that the current sea level rise rate on the West Coast is about 2 millimeters per year (slower than the recent global average of 3.4 millimeters per year). See below the related data from the NOAA.
The NOAA data is available here.
Sea level rise is not uniform. The map from the NOAA below shows that based on current trends, sea level is actually declining in Alaska (blue dots). Sea level is rising slightly under the global average on the West Coast (dark green dots) and slightly above average in parts of the East Coast and the South (light green dots). And, it is rising above the global average in parts of Texas and Louisiana (orange and red dots).
You can view the NOAA map at the following link: NOAA map
Quoting the NOAA on explaining the difference in sea level rise in various locations:
"The variations in sea level trends seen here primarily reflect differences in rates and sources of vertical land motion.
Areas experiencing little-to-no change in relative sea level are illustrated in green, including stations consistent
with average global sea level rise rate.
These are stations not experiencing significant vertical land motion.
Stations illustrated with positive sea level trends (yellow-to-red) are experiencing both global sea level rise,
and lowering or sinking of the local land, causing an apparently exaggerated rate of relative sea level rise.
Stations illustrated with negative trends (blue-to-purple) are experiencing global sea level rise and a greater vertical rise in the local land, causing an apparent decrease in relative sea level."
Our forecast of 3.6 inches by 2050 using the global sea level rising trend is conservative or potentially on the high side.
The BCDC 4.9 feet projection mentioned in the IJ is 16 times higher than the above projection (which is in line with the NASA/NOAA Intermediate scenario shown later)!
Dana Brechwald from BCDC is confused and confusing
Within the IJ article, Dana Brechwald from the Bay Conservation and Development Commission (BCDC) first states that the 4.9 feet by 2050 comes from BCDC. Next, she supports it by quoting NOAA forecasts to 2050 that come in 50% to 80% lower than her BCDC forecast (that suggests the 4.9 feet is way too high). Then, later she states that the 4.9 feet by 2050 comes from the California Ocean Protection Council's "extreme sea-level-scenario."
Let's look at the different data sources and understand how to interpret them.
The NASA & NOAA San Francisco Scenarios
The above projections are based on an interagency effort between NASA and the NOAA. The intersection of the two straight red lines represents sea level rise by 2050. And, they indicate that all scenarios including their uncertainty prediction intervals come in under 2 feet of sea level rise by 2050.
The Low (dark green) and Intermediate Low (light blue) scenarios come in flat near Zero.
The Intermediate scenario (blue) comes in at less than 1/4 of a foot. Interestingly, this Intermediate scenario comes very close to our linear extrapolation at 3.6 inches. That gives me comfort that even though my methodology was simple, it is well benchmarked by the NASA/NOAA interagency models which used far more complex methodology.
Even the High (pink) scenario comes in only a bit higher than a foot. All these scenarios are way under the 4.9 feet advanced by the BCDC.
California Ocean Protection Council (COPC) forecast
Here are their projected probabilities for San Francisco sea level rise.
As shown above, there is only a 31% probability that sea level rise would reach 1 foot and a 0.4% probability that it would reach 2 feet by 2050. In other words, they project a 99.6% probability that San Francisco's sea level rise will be under 2 feet.
Note that their 31% probability of reaching or exceeding 1 foot is commensurate with the highest NASA/NOAA scenario. Thus, the COPC probability at the 1-foot level is rather an aggressive forecast relative to the NASA/NOAA scenarios.
They start with 1.4 feet in actual sea level rise (at the 95th percentile of the COPC projections). This is consistent with the NASA & NOAA top scenario. As stated, the COPC associates this scenario with only a 5% probability of occurring.
To this sea level rise, BCDC adds another 3.5 feet for what they call a 100-year storm. The sum of the two gets you to the 4.9 feet.
The BCDC framework is wrong because it has little to do with Climate Change sea level rise. It has a lot more to do with the temporary impact of a 1 in a 100-year storm. This prospective storm would account for 3.5/4.9 or over 71% of the BCDC-stated sea level rise.
BCDC's 2050 scenario framework is more than confusing
They combine a permanent effect (the 1.4-foot sea level rise with a 5% probability ) with a short-term effect, the 3.5-foot storm. The latter would have an impact on sea level for just a few days at most.
Focusing on the storm, we already have King tides that reach between 6 to 8 feet throughout the November to January period. Thus, what is the big deal about this 1-in-100-year storm? We routinely have King tides that have twice the impact. Even if you would take the midpoint between the low tide and high tide, a routine King tide has as much impact as the BCDC 1-in-100-year storm.
As we speak, the King tides season has started. Over the current consecutive 7 days, two of them are forecasted to exceed 7 feet.
Any study of Climate Change sea level rise excludes short-term phenomena such as storms, tides, etc. And, the BCDC should have done the same. Their 4.9 feet by 2050 is misinformation.
The BCDC does not need to fabricate absurd scenarios, the flooding disaster is now
None of the above alleviates the fact that our existing Marin road infrastructure is already a disaster. During King Tides season access to highways 101 and 37 is often impaired; the Mill Valley to Sausalito bike path is flooded.
During King tides, the Manzanita parking lot, a major commuting hub, is completely flooded.
A compounding issue is that the mentioned highway and parking lot hub infrastructure are on grounds associated with much settling. Cal Trans indicated that the grounds on Highway 1 below the bridge have settled by 18 inches.
THE END