Projections for Sea Level Rise in the Forth National Climate Assessment
We summarize the data on past Global Mean Sea Level (GMSL) rise, on the recent increase in the rate of rise, and future projections for a century and two. The source is the Climate Science Special Report (CSSR) at
science2017.globalchange.gov
This is from the Fourth National Climate Assessment (NCA4), Volume I. Sea Level Rise is Chapter 12.
From 1901-1990, the GMSL rise was 4-5 inches. But since 1993 the rise quickened, rising about 3 inches over the 25 years from 1990-2015, giving a total 7-8 inches since 1900. Since 2005, about one third of the GMSL rise has been from thermal expansion of the ocean, and about two-thirds from land ice melting and other contributions.
The Pacific Coast ocean level rose slower, and the western Pacific rose faster, due to winds blowing westward. This has reversed since about 2012.
We look at projections for GMSL rise to 2050, 2100, and 2200, above the 2000 level, under various scenarios. The sceanarios relate to the Representative Concentration Pathways (RCP) 8.5, 4.5, and 2.6 climate forcings in Watts/meter-squared increase over the pre-industrial average, that we might have in 2100. The RCP 8.5 is possibly the do-nothing projection, which it seems we can avoid as a result of the Paris Agreement, and State and City actions in the US. This is from Tables 12.2 and 12.5. The numbers are in feet of rise.
Scenario…..2050…..2100…..2200
Low……………0.5……..1.0………1.3
Int. Low………0.8……..1.6………3.1
Intermediate.1.1……..3.3………9.2
Int. High……..1.4……..4.9……..17
High…………..1.8……..6.6……..25
Extreme……..2.1……..8.2……..32
The GMSL projected for 2050 is disruptive, but the rapid increases by 2100 and 2200 are truly shattering.
According to Table 12.3, the Intermediate-Low scenario is the middle of the likely range under RCP 2.6. The other ones depend on the possibility of ice cliff instabilities. With the instabilities, Intermediate is the middle range of RCP 4.5, Intermediate-High is the middle range of RCP 8.5, and High is the high end of the very likely range of RCP 8.5.
To me it implies the Venice model, where we all move back into the hills, raise all the low roads, abandon the first floors, and hire gondolas and gondoliers.
From maps of the US, we can see that on the US West Coast, the decade in which the 5-year flood event becomes a 0.2 year flood event, under the Intermediate scenario, becomes about 2040.
The additional Relative Sea Level (RSL) height above average highest tide in GMSL is about 2-3 feet on the West Coast for 2100. The Gulf Coast level rises an extra 4-6 feet, the Florida coast 3-4 feet, and the Eastern Coast rises an extra 4-5 feet.
The extra rise surrounding the US is due to Antarctic ice loss.
In my own opinion, we are presumably intelligent enough to avoid wars and become a sustainable and equitable civilization by 2100. However, the costs of adaptability and repairing damages might overwhelm funds needed for mitigation or clean energy conversion.
