4 ms·

Reading this, I wonder if the melting of the ice caps causes a measurable slow down in the Earth's rotation and an increase in the length of a day by moving mas

Reading this, I wonder if the melting of the ice caps causes a measurable slow down in the Earth's rotation and an increase in the length of a day by moving mass farther from the Earth's axis of rotation.

throwaway2048 6y ago
Not sure why this is downvoted, this is absolutely the case, but the effect is small https://climate.nasa.gov/faq/30/if-all-of-earths-ice-melts-and-flows-into-the-ocean-what-would-happen-to-the-planets-rotation/ https://climate.nasa.gov/faq/30/if-all-of-earths-ice-melts-a...
- foota 6y ago
  I'm surprised by the magnitude of the effect. I wouldn't have expected things to move around enough for the length of a day to vary by a millisecond?
  - kd5bjo 6y ago
    It doesn’t mention what sort of frequency those variations happen at. If the variation is caused primarily by plate tectonics, it might take a year or more to swing between the two extremes.
- quietbritishjim 6y ago
  Excellent link, thanks! Here are some key points for convenience (although the article's so short that this is practically half of it): > the rate of rotation varies by up to a millisecond per day [regardless of ice melting] > Melting land ice ... will change the Earth’s rotation only if the meltwater flows into the oceans > For example, if the Greenland ice sheet were to completely melt and the meltwater were to completely flow into the oceans, then ... the length of the day [would become] longer ... by about two milliseconds > Melting sea ice, such as the Arctic ice cap, does not change sea level because the ice displaces its volume and, hence, does not change the Earth’s rotation.
DiogenesKynikos 6y ago
Small changes in the rotation rate of the Earth (primarily due to seismic activity and the tidal interaction with the Moon, I think) are the reason why sidereal (or Solar) time diverges from time as kept by an atomic clock (the atomic clock has errors too, but they're orders of magnitude smaller). This is how you get different definitions of "Universal Time": * UT1 = sidereal time, based on measurements of the angles of distant quasars. * UTC = atomic clock time, with offsets added in whenever it gets too far (about 1 second) from UT1. One final fun thing about UTC. Why is it UTC? * Coordinated Universal Time = CUT ? * Universal Coordinated Time = UCT ? * Temps Universel Coordonné = TUC ? UTC was chosen precisely because it doesn't correspond to either the English or French acronym.
- quesera 6y ago
  > UTC was chosen precisely because it doesn't correspond to either the English or French acronym. That's fascinating, I assumed it was a French acronym. "Universale Temps Coordinaté" (I do not speak French, but I have seen Kentucky Fried Chicken signs in Québec!) :) Regardless of the political process of selection, I am glad things worked out the way they did. The other acronym possibilities are really unpleasant in English.
- Arcorann 6y ago
  A few comments: * Sidereal time is different from solar time; sidereal time measures the Earth's rotation relative to the stars, while solar time measures it relative to the Sun, which moves relative to the stars. Thus, UT1 and sidereal time have different rates. * Wikipedia's page on day length fluctuations (https://en.wikipedia.org/wiki/Day_length_fluctuations https://en.wikipedia.org/wiki/Day_length_fluctuations) has a discussion of the influences involved. It also has a handy graph, from which we can see that the average day length is around 2 milliseconds shorter than in the 1970s (hence why we had a leap second every year from 1973-1979, but the last leap second was over four years ago). * There's also UT2 and UT0. UT2 has a corrections for seasonal variations, while UT0 is derived from raw observations, without correcting for polar motion like UT1. These are rarely used.
  - DiogenesKynikos 6y ago

throwaway2048 6y ago

Not sure why this is downvoted, this is absolutely the case, but the effect is small https://climate.nasa.gov/faq/30/if-all-of-earths-ice-melts-and-flows-into-the-ocean-what-would-happen-to-the-planets-rotation/ https://climate.nasa.gov/faq/30/if-all-of-earths-ice-melts-a...

foota 6y ago
I'm surprised by the magnitude of the effect. I wouldn't have expected things to move around enough for the length of a day to vary by a millisecond?
- kd5bjo 6y ago
  It doesn’t mention what sort of frequency those variations happen at. If the variation is caused primarily by plate tectonics, it might take a year or more to swing between the two extremes.
quietbritishjim 6y ago
Excellent link, thanks! Here are some key points for convenience (although the article's so short that this is practically half of it): > the rate of rotation varies by up to a millisecond per day [regardless of ice melting] > Melting land ice ... will change the Earth’s rotation only if the meltwater flows into the oceans > For example, if the Greenland ice sheet were to completely melt and the meltwater were to completely flow into the oceans, then ... the length of the day [would become] longer ... by about two milliseconds > Melting sea ice, such as the Arctic ice cap, does not change sea level because the ice displaces its volume and, hence, does not change the Earth’s rotation.

DiogenesKynikos 6y ago

Small changes in the rotation rate of the Earth (primarily due to seismic activity and the tidal interaction with the Moon, I think) are the reason why sidereal (or Solar) time diverges from time as kept by an atomic clock (the atomic clock has errors too, but they're orders of magnitude smaller). This is how you get different definitions of "Universal Time": * UT1 = sidereal time, based on measurements of the angles of distant quasars. * UTC = atomic clock time, with offsets added in whenever it gets too far (about 1 second) from UT1. One final fun thing about UTC. Why is it UTC? * Coordinated Universal Time = CUT ? * Universal Coordinated Time = UCT ? * Temps Universel Coordonné = TUC ? UTC was chosen precisely because it doesn't correspond to either the English or French acronym.

quesera 6y ago
> UTC was chosen precisely because it doesn't correspond to either the English or French acronym. That's fascinating, I assumed it was a French acronym. "Universale Temps Coordinaté" (I do not speak French, but I have seen Kentucky Fried Chicken signs in Québec!) :) Regardless of the political process of selection, I am glad things worked out the way they did. The other acronym possibilities are really unpleasant in English.
Arcorann 6y ago
A few comments: * Sidereal time is different from solar time; sidereal time measures the Earth's rotation relative to the stars, while solar time measures it relative to the Sun, which moves relative to the stars. Thus, UT1 and sidereal time have different rates. * Wikipedia's page on day length fluctuations (https://en.wikipedia.org/wiki/Day_length_fluctuations https://en.wikipedia.org/wiki/Day_length_fluctuations) has a discussion of the influences involved. It also has a handy graph, from which we can see that the average day length is around 2 milliseconds shorter than in the 1970s (hence why we had a leap second every year from 1973-1979, but the last leap second was over four years ago). * There's also UT2 and UT0. UT2 has a corrections for seasonal variations, while UT0 is derived from raw observations, without correcting for polar motion like UT1. These are rarely used.
- DiogenesKynikos 6y ago