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Two recent studies have brought new attention to the issue of sea level rise.

Researchers at the Australian National University have compared today’s sea levels with those approximately 125,000 years ago in the last interglacial period when the Earth was only 1 degree Celsius warmer than today. And the United Nations Environmental Program issued its annual Emission Gap report.

The conclusions of both should be of great concern.

The Australian analysis concluded that “sea levels rose 10 meters (32.8 feet) above present levels during the Earth’s last warm period 125,000 years ago.” This rise occurred over centuries at an estimated 3 meters per 100 years. This is far more than the United Nations’ Intergovernmental Program on Climate Change has estimated.

Its estimates for the year 2100, depending on assumptions, have been from .7 to 1 meter (the results largely leave out large mass loss from Antarctic ice shelves).

The UN’s World Meteorological Organization reports that greenhouse gasses today are at record levels. CO2 is measured at 410 ppm today, almost twice the CO2 levels noted in the interglacial period 125,000 years ago of 280 ppm. CO2, along with other greenhouse gasses methane and nitrous oxide, are major contributors to a warming planet.

With global emissions continuing to increase approximately 1.5% annually, the Earth has warmed 1 degree Celsius already since pre-industrial times in the late 1700s. The Paris Climate Accords of 2016 proposed a limit of no more than 2 degree Celsius. Projections now are for temperatures to rise 3.9 degrees Celsius by the year 2100.

“According to scientific models, that kind of temperature rise sharply increases the likelihood of extreme weather events, the accelerated melting of glaciers and swelling seas” concluded the New York Times. The WMO Director General has commented that the last time the Earth had comparable CO2 levels “sea level was 10 to 20 meters higher than now.”

In an article for the Pacific Forum (No. 63, pacnet@pacforum.org, Nov. 26) I wrote “… most estimates of future sea level rise are based on tidal data of the past century and more recently on satellite data. This does not account for previously unobserved sudden disruptions, such as rapid concurrent melting of both Antarctic Greenland/Arctic ice.”

It is such a “black swan” event (i.e., something not anticipated) that could drive the degree of sea level rise and its timing. Scientists’ most recent observations of the rate of melting in both the Arctic and Antarctic exceed earlier estimates.

Seas Will Reach Fort Shafter

The Australian researchers concluded “melting ice from Antarctica was the main driver of sea level rise in the last interglacial period.” The Washington Post in an editorial (Oct. 21) noted that the effects of sea level rise (coupled with major storms and king tide events) will be evident by 2050, within the lifetime of anyone born after 1980.

There are no facts about the future, so understanding the assumptions that underlie estimates of the future is important. Scientists differ on the severity and timing of sea level rise but not on the trend. A 3 meter rise in sea levels is now seen as possible this century (or soon thereafter).

What is the impact on Hawaii?

Using an interactive flood map () set at a sea level rise for both 3 and 10 meters indicates the following:

• On Kauai, at 3 meters, Hanalei will flood to a depth of a meter, and the small boat harbor at Nawiliwili will flood. On the south coast much of Waimea will be under 2 meters of sea water. At 10 meters the south coast, including Waimea and the Pacific Missile Range, will be up to 7 meters underwater. Hanalei will be flooded to 5 meters; much of Nawiliwili to about a meter.
• On Oahu, the economic center of the state, at 3 meters there will be major flooding along the southern coast from Diamond Head to Barbers Point. Waikiki, Kakaako, downtown, and Kalihi will flood up to the H1 highway. Seas will reach the gates of Fort Shafter. Facilities at Pearl Harbor will be inundated to mauka of Kamehameha Highway. Ewa Beach will be under 1 meter. Kailua floods from the marsh side, and Enchanted Lake will be ocean to a depth of 2 meters. The area from Haleiwa to Waialua will flood to 2 meters. At 10 meters the southern shore from Diamond Head to Ewa to Barbers Point disappears by as much as 9 meters. Ford Island is gone. Seas will extend mauka to the H1-H2 interchange above Pearl City. Hawaii Kai is up to 9 meters under water. Kailua floods completely past Enchanted Lakes. Downtown Haleiwa will be under 9 meters of sea.
• At 3 meters most hotels at Kaanapali on Maui are inundated. Downtown Lahaina floods to 2 meters as does much of Kihei. Much of downtown Kahului floods. At 10 meters each will be submerged up to 9 meters, including the entire airport.
• At 3 meters downtown Hilo floods. The highway at Kailua-Kona is interdicted by the sea. At 10 meters much of Hilo and the airport will be underwater by 5 to 6 meters; the Kona airport to a lesser, but still inoperable, 2 meters.
• Papahanaumokuakea Maritime National Monument will largely disappear at 3 meters and completely at 10 meters.

The trend in estimates of sea level rise have become “more dire as more data is collected and analyzed. The rate of sea level rise is now projected to be more rapid than estimates of only a few years ago.” (Pacific Forum No. 63.). That will not change as long as greenhouse gas emissions continue to increase. The year 2100 is only an arbitrary point in time. With continued global warming sea level rise will continue for centuries, as suggested by the conclusions of the Australian scientists examining the last interglacial period.

The nearer term effects (severe storms, flooding from king tides, the dissolving of coral reefs due to ocean acidification, and uncomfortable increases in air temperature) will be evident by mid-century and at some point will make Hawaii an undesirable destination for visitors.

Even with mitigation efforts the long-term future of the Hawaiian Islands, like many island groups around the world, is bleak.