Science Snippets: Paradise Lost?

Draft script:

I remember when Popular Mechanics was all about automobiles. Long before there was such a thing as online stories, this magazine had great stories about vehicles. When I was a kid, I never imagined this outlet would be publishing serious stories about anthropogenic climate change. More recently, the online version of Popular Mechanics has been printing excellent articles about climate change and other topics. They go well beyond muscle cars.

One recent effort from Popular Mechanics was published 18 March 2025. The article is titled Hawaii Is Sinking 40 Times Faster Than Scientists Thought It Was. The subhead reads “Some parts of the island chain have a 0.6 millimeter-per-year subsidence rates, but others are in a much more dire state.”

The article begins with three bullets points: (1) “As islands like O’ahu very slowly drift from the magmatic hotspot that once formed it, the island’s weight is slowly causing it sink into the ocean at around 0.6 millimeters per year”; (2) “However, a new study shows that in some areas of O’ahu, that subsidence rate can be as high as 25 millimeters per year, roughly 40 times faster than expected”; and (3) “Researchers believe this is largely due to some areas, such as the more industrial Mapunapuna region, experiencing compaction as it was originally built on sediment and artificial fill.”

I’ve visited Hawaii a few times. Named the Sandwich Islands by Captain James Cook in 1778 to honor the Fourth Earl of Sandwich, the chain of islands is beautiful. The most common greeting in Hawaii is “how’s it?” This is a Hawaiian resident’s version of hello.

The Hawaiian Islands are well known to be growing, with the Big Island as the youngest. The big island is still growing, as indicated by recent lava flows. The oldest island in the chain of Hawaiian Islands is Kauai, which formed about 5.1 million years ago via volcanic activity. Kauai is sometimes called the Garden Island because its age and location have facilitated the development of high biological diversity. In contrast, the big island—called Hawaii—is less than half-a-million years old, with many areas still experiencing volcanic activity. The Big Island continues to grow as a result of this volcanic activity. Some areas of the big island are a few seconds old. Among the more spectacular phenomena I have observed is the volcanic activity from the safety of watercraft a few hundred meters offshore from the Big Island.

Back to the story in Popular Mechanics, where we read a short history of the island chain. “The geologic story of Hawaii has historically been one of ascension. More than a million years ago, when the Pacific Island Plate moved atop a volcanic hotspot rising through the Earth’s crust, sea-level volcanic islands formed what eventually became the U.S.’s 50th state. Now, a new study from the University of Hawai’i at Manoa reports that the island chain may be reversing course—literally.

Published in the journal Communications Earth & Environment, the study analyzes subsidence (the gradual caving in or sinking of an area) on the island of O’ahu, home of Pearl Harbor and the state capital, Honolulu. [The researchers] found that in some areas of the island, located 185 miles northwest of the Big Island … which rests on top of the island chain’s hotspot, the subsidence rate was at around just 0.6 millimeters per year. However, they also recorded areas that were sinking a stunning 40 times that rate at roughly 25 millimeters per year. This rate, along with the localized nature of the subsidence, is what caused researchers to raise a few eyebrows.”

What’s the big deal? As you can probably imagine, many areas on island chains are susceptible to flooding. The lead author of the peer-reviewed paper reported in the Popular Mechanics article is quoted in a press statement: “Our findings highlight that subsidence is a major, yet often overlooked, factor in assessments of future flood exposure. In rapidly subsiding areas, sea level rise impacts will be felt much sooner than previously estimated, which means that we must prepare for flooding on a shorter timeline.”

If you don’t live in Hawaii, this seems as if it’s no big deal. If you do live in Hawaii, especially if you live in Oahu, it’s definitely a big deal. Consider the peer-reviewed paper mentioned in Popular Mechanics, which was created by four scholars and published on 19 February 2025. Titled Coastal land subsidence accelerates timelines for future flood exposure in Hawai’i, the peer-reviewed paper was published in Communications Earth & Environment. The Abstract of this open-access paper includes this information: “Coastal subsidence exacerbates relative sea level rise, making low-lying areas vulnerable to flooding. In Hawai’i, the contribution of vertical land motion has not been fully studied. This is critical for urban O’ahu, where infrastructure is on low-lying coastal areas with varying sedimentary consolidation. Here we processed Interferometric Synthetic Aperture Radar data from 2006–2024 for the Hawaiian Islands, referencing them with Global Navigation Satellite System measurements to calculate subsidence rates. We also created a two-meter resolution digital elevation model for coastal O’ahu using 2007–2013 Federal Light Detection and Ranging data, which included hydro-enforcement and gap filling with reprocessed data. Using this elevation data and vertical land motion measurements, we numerically modeled flood exposure. Results suggest that while island-wide subsidence on O’ahu is about 0.6 ± 0.6 mm/yr, the south shore has localized rates exceeding 25.0 ± 1.0 mm/yr. This subsidence, which is much faster than Hawaii’s long-term sea level rise rate …, could expand flood exposure …. Accounting for subsidence compresses the timeline for flood preparedness …, emphasizing the need to integrate these insights into planning and policy for sustainable development and flood mitigation.” If you’ve ever lived in a house that is settling, then you have noticed cracks in the walls. This is an uncomfortable experience.

The bottom line comes in the final paragraph of the Discussion section of the peer-reviewed paper: “Our study highlights the need for subsidence to be considered when assessing the impacts of rising sea level, and adaptation strategies must account for both … [sea level rise] and land subsidence together. For future work, these results can be further combined with analysis of other processes that are known to exacerbate flood exposure for a more complete estimate of future flood exposure. ... The combined effects of any number of these types of processes … can lead to much greater flood exposure.”

Hawaii is an amazing place. Its urban flooding problem is emblematic of other areas, especially those surrounded by oceans. The typically human approach of taking the short, money-driven approach is fully on display in Hawaii. Had we always employed a perspective focused on many generations in the future, we would not be facing the issue of flooding. For that matter, many of our problems would have never arisen.