Notes on Sweet and others (2022) Seal Level Rise

Earlier this year Sweet and others(2022) updated Sweet and others (2017): Global and Regional Sea Level Rise Scenarios for the United State. Sweet and others (2017) suggested global sea level (GMSL) will rise as between 0.3 meters and 2.5 meters by 2100. Sweet and others (2022) find the high end of 2.5 m by 2100 less plausible. The bad news is that the rate of GMSL rise has been increasing and Sweet and others (2022) project that the rise in GMSL over the next 30 years will be as much as that over the past 100 years. The 2022 report notes a high level in confidence for their sea level rise scenarios over the next 30 years. Post 30 years the confidence level for sea levels is lower primarily because of uncertainty regarding some of the ice sheets in Greenland and Antarctica.  

GMSL is not simple and the sea level rise is not uniform around the planet. Some places will see greater sea level rise and others less. The 2017 report included an image of global sea level rise from 1992 to 2016 derived from satellite data measurements. 

 

Figure from Sweet and others (2017)

Global sea level has rises in an uneven manner due to currents, warm water expansion, and changes to gravity fields from more water in the oceans (the Earth's surface is flexible). The sea level also can vary due to cyclical climate patterns that move the ocean water around via wind and temperature patterns. I like to think that the ocean layer as having weather only slower and a bit less pronounced than the atmosphere. The image above also shows that on the Washington State coast the global sea level trend was near neutral for the 1992-2016 time period.

The 2022 report has an image with three plots showing global sea level rise along the coast of North America. 

Figure 2.1 from Sweet and others (2022) Regional sea level linear rates of rise (mm/year) from satellite altimetry over three different time periods: (a) 1993–2006, (b) 2007–2020, and (c) 1993–2020. Linear rates of change of relative sea level (ocean and land height changes) from tide gauges over the same time period are also shown (circles). 

For Washington State the 1993 to 2006 period the regional sea level rise was mostly neutral, but the more recent period of 2007 to 2020 shows that regional sea level on the Washington coast has increased as has the regional rates in most places around North America. 

The global and regional sea level increase is not a simple uniform rise. There is an added complexity: while regional sea level is changing, the land next to the sea is also changing in level. More on that on a future soon post.

The Two Hat Islands in Washington State

I visited Hat Island in Possession Sound west of Everett this week. The icy thick fog in the morning prevented a good picture of the island, but but I had a nice view from the island. 

View from a high bluff on Hat Island looking south to the Mukilteo Ferry and Whidbey Island coast

Just the week before I had a nice view of Hat Island in Padilla Bay east of Anacortes. 

Hat Island viewed from the west in Guemes Channel 

How can there be two Hat Islands in the same state?  

If one zooms in on the USGS National Map the Possession Sound Hat Island has two names.  

I have always thought of the island in Possession Sound as Hat Island. The community of homes and lots on the island is called Hat Island and the ferry (private) is the Hat Island Ferry. However, its official name on the USGS topographic map is Gedney Island. The name was given to the island by Wilkes following a common custom of the time of the random naming things for associates or friends that never came near the area. Waterman (2017) provides some background on Gedney and his role in the La Amistad case. Gedney's claims on the La Amistad and it cargo may explain why locals preferred using the name Hat Island. 

The Hat Island in Padilla Bay is a Washington State Natural Resource Conservation Area. Perhaps an official name change is in order for one or both of the Hats.