Comment by AbrahamParangi
2 years ago
Yeah I don’t know that this even makes sense at a glance. How much mass do we expect just moves around by natural processes? Should we even expect to be able to detect an effect of this magnitude (as in, distinguish it from noise)? I do not think so:
- Based on a cursory search, a large iceberg may weigh in at ~1 trillion tons. The calving process moves mass hundreds of kilometers away from Antarctica. This should be an effect of similar magnitude!
- The water cycle moves ~500 trillion tons of water each year. This water is moved hundreds of kilometers and isn’t evenly distributed over the course of a year. We should expect the impact of seasonal fluctuations in water distribution to thus have a comparatively much larger impact on the earth’s rotation.
I don’t think these numbers add up. I think we’re reading this story because it feeds into a certain kind of “we are hurting Mother Earth” mindset.
The largest iceberg ever measured, B-15, had a mass of about three billion tons. Still enormous, but not trillions, which sounded unbelievable enough to prompt me to look.
https://en.m.wikipedia.org/wiki/Iceberg_A-68
A-68 was part of Larsen C, a section of the Larsen Ice Shelf. Scientists found the crack beginning to form in November 2016. Scientists assess that A-68 "didn't just break through in one clean shot, [but] it formed a lace-network of cracks first."[5] The resulting iceberg was around 175 km long and 50 km wide, 5,800 km² in area, 200 m thick and weighed an estimated one trillion tonnes.[8][5]
I’m not sure if Wikipedia is right here however because the linked sources have changed to remove mentions of mass.
That said we should be able to do a pretty dumb calculation. 1 km3 of water weighs ~1 gt.
5800 km2 x 0.2 km = 1160 km3
1160 km3 of ice x 0.9 (density of ice compared to water) x 1 gt / 1 km3 leaves us with a mass of about 1044 gt or around 1 trillion tons.
Edit: also, I am not able to find an original source for the mass of B-15 being in the few billions range
The calving process results in ice already floating in water moving. Archimedes' law means the effect is very limited ~ the height the ice sticks above the surface and the little change in density.
More importantly, the article mentions removing annual effects on Polar Motion. They are averaging - somehow - to look at permanent changes. The annual effects may be an order of magnitude greater, it is not relevant.