5 ms·

Most of these ice mass measurements are made using GRACE not physical height / GPS measurements. Ice mass loss appears to be accelerating by multiple forms of m

Most of these ice mass measurements are made using GRACE not physical height / GPS measurements. Ice mass loss appears to be accelerating by multiple forms of measurement. https://www.nasa.gov/mission_pages/Grace/index.html https://www.nasa.gov/mission_pages/Grace/index.html

credit_guy 8y ago
Fine, it's GRACE. So GRACE has an accuracy of 0.001%? Really? Or rather, is there any estimation technique to measure the ice mass of a whole continent with accuracy of one thousandth of one percent? 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_Experiment https://en.wikipedia.org/wiki/Gravity_Recovery_and_Climate_E... [2]https://www.nature.com/articles/s41586-018-0179-y https://www.nature.com/articles/s41586-018-0179-y [3]https://en.wikipedia.org/wiki/East_Antarctic_Ice_Sheet https://en.wikipedia.org/wiki/East_Antarctic_Ice_Sheet
- breakyerself 8y ago
  Yeah, but that same study showed that the rate of gains was slowing and more recent work by the same people using the same processes show it is now shedding mass.
- flukus 8y ago
  > Fine, it's GRACE. So GRACE has an accuracy of 0.001%? Really? Or rather, is there any estimation technique to measure the ice mass of a whole continent with accuracy of one thousandth of one percent? 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.
  - credit_guy 8y ago
    >Your argument is misleading because it assumes uniform ice loss across the continent I'm not assuming that. "Average" and "uniform" are two different things. I never said anything about "uniform". Take a look at the ice loss visualization [1] from NASA's website. On the west side there are ice losses as high as 300m (dark red), on the east side some ice gains of about 100m (light blue). All those losses and gains are estimated with some instruments. If you are in one of the areas where the ice loss was estimated to be about 100m, you look at your initial elevation, final elevation and take the difference. Will you elevation difference be -100m, or -98m? There will be some measurement uncertainty. Overall, uncertainties from different instruments tend to cancel out, that't the law of large numbers. Overall, I doubt we have that many numbers (or so little individual measurement uncertainty to begin with) to end up with a final measurement uncertainty that is so small. Take a look at article [2] about the estimation of precipitations in Antarctica. It was published in March 2018 in the journal "Polar Science" owned by Elsevier, which as far as I can tell does not publish junk articles. The general tone is that there are large uncertainties in the estimation of precipitation in Antarctica. "The study of Antarctic precipitation has attracted a lot of attention recently. The reliability of climate models in simulating Antarctic precipitation, however, is still debatable" "The current method of data collection relies on measurement with limited temporal basis, with distances between measurements exceeding 1300 km (Knuth et al., 2010). This makes instrumental-based measurement of precipitation in Antarctic highly unreliable (Genthon et al., 2003)." Of course, such an article does not get much press. How would one report it? "New research shows large uncertainties in our understanding of the mass balance in Antarctica" ? [1] https://svs.gsfc.nasa.gov/30880 https://svs.gsfc.nasa.gov/30880 [2]https://www.sciencedirect.com/science/article/pii/S1873965217300981 https://www.sciencedirect.com/science/article/pii/S187396521...

credit_guy 8y ago

Fine, it's GRACE. So GRACE has an accuracy of 0.001%? Really? Or rather, is there any estimation technique to measure the ice mass of a whole continent with accuracy of one thousandth of one percent? 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_Experiment https://en.wikipedia.org/wiki/Gravity_Recovery_and_Climate_E... [2]https://www.nature.com/articles/s41586-018-0179-y https://www.nature.com/articles/s41586-018-0179-y [3]https://en.wikipedia.org/wiki/East_Antarctic_Ice_Sheet https://en.wikipedia.org/wiki/East_Antarctic_Ice_Sheet

breakyerself 8y ago
Yeah, but that same study showed that the rate of gains was slowing and more recent work by the same people using the same processes show it is now shedding mass.
flukus 8y ago
> Fine, it's GRACE. So GRACE has an accuracy of 0.001%? Really? Or rather, is there any estimation technique to measure the ice mass of a whole continent with accuracy of one thousandth of one percent? 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.
- credit_guy 8y ago
  >Your argument is misleading because it assumes uniform ice loss across the continent I'm not assuming that. "Average" and "uniform" are two different things. I never said anything about "uniform". Take a look at the ice loss visualization [1] from NASA's website. On the west side there are ice losses as high as 300m (dark red), on the east side some ice gains of about 100m (light blue). All those losses and gains are estimated with some instruments. If you are in one of the areas where the ice loss was estimated to be about 100m, you look at your initial elevation, final elevation and take the difference. Will you elevation difference be -100m, or -98m? There will be some measurement uncertainty. Overall, uncertainties from different instruments tend to cancel out, that't the law of large numbers. Overall, I doubt we have that many numbers (or so little individual measurement uncertainty to begin with) to end up with a final measurement uncertainty that is so small. Take a look at article [2] about the estimation of precipitations in Antarctica. It was published in March 2018 in the journal "Polar Science" owned by Elsevier, which as far as I can tell does not publish junk articles. The general tone is that there are large uncertainties in the estimation of precipitation in Antarctica. "The study of Antarctic precipitation has attracted a lot of attention recently. The reliability of climate models in simulating Antarctic precipitation, however, is still debatable" "The current method of data collection relies on measurement with limited temporal basis, with distances between measurements exceeding 1300 km (Knuth et al., 2010). This makes instrumental-based measurement of precipitation in Antarctic highly unreliable (Genthon et al., 2003)." Of course, such an article does not get much press. How would one report it? "New research shows large uncertainties in our understanding of the mass balance in Antarctica" ? [1] https://svs.gsfc.nasa.gov/30880 https://svs.gsfc.nasa.gov/30880 [2]https://www.sciencedirect.com/science/article/pii/S1873965217300981 https://www.sciencedirect.com/science/article/pii/S187396521...