I had heard about similar effects from hydro dams.
Reconciling past changes in Earth’s rotation with 20th century global
sea-level rise: Resolving Munk’s enigma
Jerry X. Mitrovica1,*, Carling C. Hay1,2, Eric Morrow2, Robert E.
Kopp2,3, Mathieu Dumberry4,5 and Sabine Stanley6
+ Author Affiliations
↵*Corresponding author. E-mail: [email protected]
Science Advances 11 Dec 2015:
Vol. 1, no. 11, e1500679
DOI: 10.1126/sciadv.1500679
http://advances.sciencemag.org/content/1/11/e1500679
Abstract
In 2002, Munk defined an important enigma of 20th century global mean
sea-level (GMSL) rise that has yet to be resolved. First, he listed
three canonical observations related to Earth’s rotation [(i) the
slowing of Earth’s rotation rate over the last three millennia
inferred from ancient eclipse observations, and changes in the (ii)
amplitude and (iii) orientation of Earth’s rotation vector over the
last century estimated from geodetic and astronomic measurements] and
argued that they could all be fit by a model of ongoing glacial
isostatic adjustment (GIA) associated with the last ice age. Second,
he demonstrated that prevailing estimates of the 20th century GMSL
rise (~1.5 to 2.0 mm/year), after correction for the maximum signal
from ocean thermal expansion, implied mass flux from ice sheets and
glaciers at a level that would grossly misfit the residual
GIA-corrected observations of Earth’s rotation. We demonstrate that
the combination of lower estimates of the 20th century GMSL rise (up
to 1990) improved modeling of the GIA process and that the correction
of the eclipse record for a signal due to angular momentum exchange
between the fluid outer core and the mantle reconciles all three Earth
rotation observations. This resolution adds confidence to recent
estimates of individual contributions to 20th century sea-level change
and to projections of GMSL rise to the end of the 21st century based
on them.
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Fig. 1Munk’s enigma of global sea-level rise (/1/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-1>).
(*A*) Clock error from 500 B.C.E. to 1600 C.E. inferred from untimed
partial solar eclipses (magenta; arrows reflect allowable bounds) and
untimed total and annular solar eclipses (blue lines) listed in Appendix
B of Stephenson (/4/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-4>) [see
also Stephenson and Morrison (/3/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-3>)]. The
green line represents the clock error associated with the slowing of
Earth’s rotation due to tidal dissipation (TD) (/3/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-3>,/6/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-6>). The
red line represents the clock error computed by adding to the green line
the signal due to GIA, as predicted using the VM1 viscosity profile
(/13/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-13>,/14/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-14>) and
the ICE-5G ice history (/15/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-15>).
(*Inset*) Change in the rotation period associated with the red and
green lines in the main frame, also plotted relative to the value for
1820 C.E. (*B*) Rate of change of the/J/_2 harmonic from 1976 to 1990.
The shaded region represents the satellite-derived (/7/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-7>–/9/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-9>)
observational constraint on the secular rate of change in the/J/_2
harmonic from 1976 to 1990. The red dot represents the predicted/J/_2
rate due to ongoing GIA computed using the VM1 viscosity model (/13/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-13>,/14/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-14>) and
the ICE-5G ice history (/15/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-15>). The
blue bar represents the correction to the GIA prediction associated with
the melting of glaciers (including those at the periphery of the
Greenland Ice Sheet) tabulated by Vaughan/et al./(/18/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-18>). The
vertical range of the blue bar reflects the uncertainty in this melt
contribution (0.7 ± 0.1 mm/year). The right ordinate scale maps the/J/_2
rate into an associated acceleration of Earth’s axial rate of rotation
(/11/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-11>).
(*C*) TPW rate over the 20th century. The black arrow with error ellipse
represents the secular rate of TPW relative to mantle reference frames
as inferred from astronomic and geodetic data (/12/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-12>).
(The black arrow at the bottom left of the map shows the amplitude scale
for the TPW vector.) The dashed red line and the solid red line
represent the TPW vector associated with ongoing GIA computed using the
viscosity model VM1 and either the standard (/11/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-11>) or
the revised ice age rotational stability theory (/21/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-21>),
respectively. The blue line represents the TPW signal driven by the
melting of glaciers (/18/
<http://advances.sciencemag.org/content/1/11/e1500679.full#ref-18>). The
fact that the GIA predictions based on the VM1 viscosity model (and, in
the case of the TPW datum, the old rotation theory) fit all three
rotation observables and do not allow for any excess signal associated
with modern ice mass flux. Frame (B) defines Munk’s enigma.
http://www.mnn.com/earth-matters/climate-weather/stories/rising-sea-levels-will-slow-down-earths-rotation
*Rising sea levels will slow down Earth's rotation*
Longer days are yet another profound consequence of global warming.
BRYAN NELSON
December 14, 2015, 9:34 p.m.
Global warming
<http://www.mnn.com/earth-matters/wilderness-resources/photos/11-ways-the-world-as-we-know-it-could-end/global-warming>is
causing glaciers to melt at unprecedented speeds, which in turn is
causing sea levels to rise worldwide. Now scientists have confirmed yet
another deleterious effect of this process: It is causing the planet's
rotation to slow down, according to a new studyrecently published in
Science Advances <http://advances.sciencemag.org/content/1/11/e1500679>.
The speed of Earth's rotation is affected by a number of things, such as
the shifting behavior of the planet's molten core, and even by a force
called tidal acceleration, which is caused by the gravitational dance
between Earth and themoon
<http://www.mnn.com/earth-matters/space/photos/how-much-do-you-know-about-the-moon/lunar-mystery>.
But the shifting mass of the world's water, as it goes from being frozen
as ice to free-flowing in the seas, should also have a measurable effect.
Since human-caused global warming has led to a marked acceleration in
sea level rise, especially over the last century, then the Earth's
rotational speed should have a correlative change as well. At least,
that's been the assumption. But observational data to confirm this
correlation have been scant — until now.
*PHOTO BREAK:**6 island nations threatened by climate change*
<http://www.mnn.com/earth-matters/climate-weather/photos/6-island-nations-threatened-by-climate-change/rising-anxiety>
Using a combination of calculations and computer modeling, a team of
researchers led by Jerry Mitrovica of Harvard University have finally
confirmed the effect. It turns out that Earth’s rotation has slowed by
16,000 seconds, or about 4.5 hours, since 500 B.C. According to
Mitrovica's team, 6,000 seconds of this can be blamed specifically on
changing sea levels.
Much of the change in sea level during this period of time has been due
to the natural process of glacial recession since the last ice age, but
the team was able to correct previous miscalculations about the
correlation between sea level change and Earth's rotational spin by
factoring in updated numbers on 20th century sea level changes, among
other things.
It can therefore be expected that as sea levels continue to rise,
Earth's rotation will continue to slow down. Although this effect only
amounts to a few seconds each year, which is not really perceptible, it
further goes to show just how profoundly modern climate change is
capable of disrupting our planet.
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