Rising Sea Levels Making Days Longer? – Watts Up With That?

Guest “I Couldn’t Make This Slate, Even If I Tried” by David Middleton

‘Unprecedented’ sea level rise is making days longer on Earth

Published July 15, 2024 at 3:00 PM EDT

Via Jess Thomson

Science reporter

Climate change is impacting our planet in many ways—from powerful storms and severe droughts to invasive species and ocean acidification—but there may be another strange impact you haven’t heard about.

Climate change may actually be gradually changing the length of a day on Earth, according to a new paper in the journal Nature. Proceedings of the National Academy of Sciences.

This is the result of rising sea levels – due to rising temperatures and melting polar ice – which in turn causes a redistribution of mass from our planet’s poles towards the equator.

[…]

Newsweek

NewsweekAre they still in business?

PNAS articles are paid. However, the abstract says it all…

abstract

Melting of global ice sheets and glaciers leads to rising sea levels, and mass transport from the poles to the equator increases the Earth’s oblateness and leads to an increase in the length of day (LOD). Here, we use observations and reconstructions of mass variations on the Earth’s surface since 1900 to show that the climate-induced LOD trend fluctuated between 0.3 and 1.0 ms/cy during the 20th century, but has accelerated to 1.33 ± 0.03 ms/cy since 2000. We further show that surface mass transport fully explains the observed acceleration in oblateness over the past three decades. We present an independent measure of the decreasing LOD trend due to Glacial Isostatic Adjustment (GIA) of −0.80 ± 0.10 ms/cy, providing a constraint on mantle viscosity. The sum of this GIA rate and lunar tidal friction fully explains the secular LOD trend inferred from the eclipse record over the past three millennia prior to the onset of contemporary climate change. Projections of future climate warming under high emissions scenarios suggest that the climate-induced LOD rate could reach 2.62 ± 0.79 ms/cy by 2100, surpassing lunar tidal friction as the most important contributor to long-term LOD fluctuations.

PNAS

That’s the model to the extreme. There’s no way to measure milliseconds per century (ms/cy) changes in the length of day (LOD) over any time period, much less on a hundred-year to decade scale. Might as well try to determine “How many angels can dance on the head of a pin?”

LOD has generally increased over geological time (Mitchell and Kirscher, 2023). As the Earth pushes the Moon farther away, the Earth’s rotation also slows down.

1.33 ms/cy = 0.0000133 seconds/year

At a rate of 0.0000133 seconds per year, in 80 million years, the stellar day will be 18 minutes longer than it is now.

Back in the Cretaceous period (about 80 million years ago), when sea levels were much higher than today and there was virtually no ice at the poles, a day was about 23.5 hours long (de Winter et al., 2020). The rate of change in LOD from 80 million years ago to the present (1950 AD) is about 2.25 ms/cy.

Let this sink in: The rate of change in LOD from 80 million years ago to 1950 AD was about +2.25 ms/cy. The rate of change in LOD since 2000 AD, attributed to “‘unprecedented'” sea level rise, is only +1.33 ms/cy.

Of course, there are no LOD measurements for the Cretaceous. This is based on reconstructions from shells and crude models… And the error bars are in days and hours… not milliseconds.

LOD measurement

LOD can now be measured directly with great precision. Schreiber et al., 2023 used “a laser ring gyroscope” to measure changes in stellar day. They found that the LOD fluctuated by up to 6 ms over a 120-day measurement period.

If the LOD fluctuates by 6 ms over a two-month period, then an increase of 1.33 ± 0.03 ms/century in LOD is related to a sea level rise rate of 1–3 mm/year associated with a daily tidal amplitude of 1 meter.

Presenter

de Winter, NJ, Goderis, S., Van Malderen, S.J.M., Sinnesael, M., Vansteenberge, S., Snoeck, C., Belza, J., Vanhaecke, F. and Claeys, P. (2020), Subdaily- Scale of chemical changes in a Torreites Sanchez Rudist Shells: Implications for Rudist Paleobiology and the Cretaceous Day-Night Cycle. Paleoceanography and paleoclimatology35: e2019PA003723. https://doi.org/10.1029/2019PA003723

Mitchell, RN, Kirscher, U. Mid-Proterozoic daylength stagnates due to tidal resonance. Geoscience Nation. 16, 567–569 (2023). https://doi.org/10.1038/s41561-023-01202-6

Schreiber, K.U., Kodet, J., Hugentobler, U. et al. Changes in the Earth’s rotation rate measured by a ring laser interferometer. Natural photons. 17, 1054–1058 (2023). https://doi.org/10.1038/s41566-023-01286-x

Shahvandi MK, Adhikari S, Dumberry M, Mishra S, Soja B. The increasingly dominant role of climate change in day length variability. Proc Natl Acad Sci US A. 2024 Jul 23; 121 (30): e2406930121. doi: 10.1073/pnas.2406930121. Epub 2024 Jul 15. PMID: 39008671.