5 ms·

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

44 points by mturmon 8y ago

macinjosh 8y ago
I find headlines like this frustrating and potentially misleading. It provides zero context. Do we know that this is abnormal? Forty years is a short period of time in the grand scheme of things. Six times more than what?
- credit_guy 8y ago
  "The team was able to discern that between 1979 and 1990, Antarctica shed an average of 40 gigatons of ice mass annually. (A gigaton is 1 billion tons.) From 2009 to 2017, about 252 gigatons per year were lost." 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.
  - shookness 8y ago
    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.
  - mturmon 8y ago
    You know less than you think you do. 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/Herring_et_al_2016_RevGeophys.pdf https://www.unavco.org/data/gps-gnss/derived-products/docs/H...
    - credit_guy 8y ago
      > You know less than you think you do. Not clear how this ad-hominem enhances your argument. >If you don’t know how they did the measurement, why are you so sure it is wrong? I'm not "so sure", I'm just skeptical. I find it hard to believe that one can estimate the net ice loss over a huge and dynamic body of ice with an accuracy better than 0.001%, using any type of measurements conceivable. You are saying that somehow the whole mass of Antarctica is irrelevant as a base mass to calculate accuracy? Why so? The ice naturally compresses and flows and this happens at continental scale. A large iceberg calving on the western coast of the continent may be offset by a relatively modest ice accumulation on the much larger eastern side. However, that accumulation on the eastern side will be conflated by the general compression that will lead to some ice being pushed towards the edges, etc, etc. There's no natural way to take a part of the continent out of the equation and say "well, we are interested only in this subset".
      - davesque 8y ago
- mturmon 8y ago
  Well, six times faster mass loss now than in the recent past. I linked this press release because it has a link to the PNAS article, which is free and describes the findings in greater detail.
- wmeredith 8y ago
  Agreed. It’s poor journalism. My response is, “so?”.
  - freethemullet 8y ago
    Is your point that humans can always ask "so?" after a proposition?
- sjg007 8y ago
  Yes. What causes ice to lose mass? Heat.
Proven 8y ago
> we expect multi-meter sea level rise from Antarctica in the coming centuries.” 1) Nonsense modeling. 20 year predictions from the 1990's turned out to be laughable, now they're predicting 200 years ahead. How about they try 2 year models, maybe they could get those right? 2) Can't see why I should care about someone's beach property in 2428. Even if their models were correct, which ch they aren't. Most people live paycheck to paycheck and these lunatics want to tax and spend their hard earned money to prevent fantasy scenarios. Truly appalling.

44 points by mturmon 8y ago

I find headlines like this frustrating and potentially misleading. It provides zero context. Do we know that this is abnormal? Forty years is a short period of time in the grand scheme of things. Six times more than what?

credit_guy 8y ago
"The team was able to discern that between 1979 and 1990, Antarctica shed an average of 40 gigatons of ice mass annually. (A gigaton is 1 billion tons.) From 2009 to 2017, about 252 gigatons per year were lost." 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.
- shookness 8y ago
  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.
- mturmon 8y ago
  You know less than you think you do. 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/Herring_et_al_2016_RevGeophys.pdf https://www.unavco.org/data/gps-gnss/derived-products/docs/H...
  - credit_guy 8y ago
    > You know less than you think you do. Not clear how this ad-hominem enhances your argument. >If you don’t know how they did the measurement, why are you so sure it is wrong? I'm not "so sure", I'm just skeptical. I find it hard to believe that one can estimate the net ice loss over a huge and dynamic body of ice with an accuracy better than 0.001%, using any type of measurements conceivable. You are saying that somehow the whole mass of Antarctica is irrelevant as a base mass to calculate accuracy? Why so? The ice naturally compresses and flows and this happens at continental scale. A large iceberg calving on the western coast of the continent may be offset by a relatively modest ice accumulation on the much larger eastern side. However, that accumulation on the eastern side will be conflated by the general compression that will lead to some ice being pushed towards the edges, etc, etc. There's no natural way to take a part of the continent out of the equation and say "well, we are interested only in this subset".
    - davesque 8y ago
mturmon 8y ago
Well, six times faster mass loss now than in the recent past. I linked this press release because it has a link to the PNAS article, which is free and describes the findings in greater detail.
wmeredith 8y ago
Agreed. It’s poor journalism. My response is, “so?”.
- freethemullet 8y ago
  Is your point that humans can always ask "so?" after a proposition?
sjg007 8y ago
Yes. What causes ice to lose mass? Heat.

Proven 8y ago

> we expect multi-meter sea level rise from Antarctica in the coming centuries.” 1) Nonsense modeling. 20 year predictions from the 1990's turned out to be laughable, now they're predicting 200 years ahead. How about they try 2 year models, maybe they could get those right? 2) Can't see why I should care about someone's beach property in 2428. Even if their models were correct, which ch they aren't. Most people live paycheck to paycheck and these lunatics want to tax and spend their hard earned money to prevent fantasy scenarios. Truly appalling.