Antarctica losing six times more ice mass annually now than 40 years ago

Antarctica losing six times more ice mass annually now than 40 years ago
news.uci.edu

I'm a climate skeptic. This type of research is why I'm a climate skeptic. 252 gigatons per year means a bit less than 0.001% of the mass of the ice sheet of the Antarctic continent. Or, to put it differently, about 1.8cm decrease in average ice height, when the current average is about 1.9km. They are telling me they have a method to estimate an average decrease of 1.8cm? Really? How can anyone claim such a thing with a straight face? Civilian GPS doesn't have this type of vertical resolution. You can achieve better resolution by the law of large numbers, however that is at the rate of the square root of the number of observations, and I doubt there are a tremendous number of observation points in Antarctica.

Wait, actually they claim their accuracy is much higher, sometimes more precise than 0.0002% or even 0.0001% (I kid you not).

Here's the wiki link for GRACE [1]. It states that during 2003-2013 the ice loss was 67±44 Gt per year. That ±44 Gt represents ±0.00017%

Anyway, here's the actual abstract of the nature article [2]

"The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992–2017 (5 ± 46 billion tonnes per year) being the least certain."

For those not familiar, East Antarctica is much bigger than West Antarctica, so it's natural for any measurement to be least certain. However, take a look at the prior estimates from the GRACE studies [3]

"An early analysis of GRACE-based studies data indicated that the EAIS was losing mass at a rate of 57 billion tonnes per year and that the total Antarctic ice sheet (including WAIS, and EAIS coastal areas) was losing mass at a rate of 152 cubic kilometers (c. 139 billion tonnes) per year.[4] A more recent estimate published in November 2012 and based on the GRACE data as well as on an improved glacial isostatic adjustment model indicates that East Antarctica actually gained mass from 2002 to 2010 at a rate of 60 ± 13 Gt/y."

This ± 13 Gt accuracy listed here is well below 0.0001%

[1] https://en.wikipedia.org/wiki/Gravity_Recovery_and_Climate_E...

[2]https://www.nature.com/articles/s41586-018-0179-y

[3]https://en.wikipedia.org/wiki/East_Antarctic_Ice_Sheet

If some areas are losing/gaining meters then your 1.8cm average is irrelevant as it's not the resolution they're looking at.

Your argument is misleading because it assumes uniform ice loss across the continent, it's a straw man you create and then destroy. Time to turn that skepticism inwards.

GPS is not part of the measurement suite in OP, but better than 1.8 cm vertical resolution from GPS has been possible since the late 1990s, using after the fact orbit determination. It is now routine to get sub-cm vertical accuracy in GPS measurements [1, fig. 3, magenta line]. The horizontal displacements are known to about a mm.

These displacements are known so accurately that you can readily measure groundwater withdrawals, the extra mass related to of high atmospheric pressure over the GPS sensor (daily cadence), and post-glacial rebound (decadal cadence).

Your remarks below about the accuracy of the GRACE gravimetric measurement are also misguided. You can’t just choose a baseline mass and say it’s impossible to measure a change in that mass to some percent accuracy. The GRACE measurement depends on how well you can measure a distance between two spacecraft, and how well you can eliminate systematics from that difference. It does not depend on a relative mass.

Anyway, the paper uses a different technique to get ice fluxes. If you don’t know how they did the measurement, why are you so sure it is wrong?

[1] https://www.unavco.org/data/gps-gnss/derived-products/docs/H...