....or is it???
http://www.nasa.gov/feature/goddard...s-of-antarctic-ice-sheet-greater-than-losses/
http://www.ingentaconnect.com/content/igsoc/jog/pre-prints/content-ings_jog_15j071
Worth noting is that IPCC had ASSUMED some sea level rise was due to Antarctic mass losses; if Antarctica is NOT losing ice, but gaining, then the sea level rise being attributed to the Antarctic is coming from somewhere else....
What is also somewhat confusing with this new data, is that these are based on altimetry (height) data of the land ice, which is showing INCREASES, due to more precipitation and snow.
HOWEVER, other authors, using gravimetric data (gravity measurements from satellites), have previously indicated an net ice LOSS for Antarctica as a whole:
https://www.princeton.edu/main/news/archive/S43/04/11E77/index.xml?section=topstories
So, who is right?
Well, looking at the two methods being applied, the gravimetric data are a DIRECT method of measuring the amount of mass at the Antarctic (ice, land, ocean). The altimetry data are actually measuring the HEIGHT of the ice there, and inferring the mass (it's not a bad method, but it is an inferred rather than a direct measurement).
So, EITHER, the gravimetric data are more inaccurate than previously assumed (that study was also this year, so it's 'new' data), OR the altimetry data are potentially being 'fooled' by variations in the density of the ice and snow. Think of it like a corked baseball bat. From the outside, you cannot tell the difference between a regular bat and a corked one, if the end is sufficiently masked or painted. BUT, if you WEIGH them both, you will find the corked one is lighter, because it is filled with less dense material.
It will be interesting to see how these to data sets are reconciled among glaciologists. In the GRACE (gravimetric data) paper from April of this year, the authors even point out the 'corked bat' or volume vs mass notion specifically:
Also worth noting...the GRACE satellites which took the gravimetric data have done so since 2002, and are due to retire in 2016; replacements are set to be launched in 2017, but I'm not sure if that will occur if Congress cuts NASA budgets for climate science.....in other words, there is potential that we could lose the MOST accurate measurement of Antarctic land ice gain or loss....
A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.
The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice.
According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed to 82 billion tons of ice per year between 2003 and 2008.
“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas.” Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”
The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice.
According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed to 82 billion tons of ice per year between 2003 and 2008.
“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas.” Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”
http://www.nasa.gov/feature/goddard...s-of-antarctic-ice-sheet-greater-than-losses/
http://www.ingentaconnect.com/content/igsoc/jog/pre-prints/content-ings_jog_15j071
Worth noting is that IPCC had ASSUMED some sea level rise was due to Antarctic mass losses; if Antarctica is NOT losing ice, but gaining, then the sea level rise being attributed to the Antarctic is coming from somewhere else....
What is also somewhat confusing with this new data, is that these are based on altimetry (height) data of the land ice, which is showing INCREASES, due to more precipitation and snow.
HOWEVER, other authors, using gravimetric data (gravity measurements from satellites), have previously indicated an net ice LOSS for Antarctica as a whole:
https://www.princeton.edu/main/news/archive/S43/04/11E77/index.xml?section=topstories
So, who is right?
Well, looking at the two methods being applied, the gravimetric data are a DIRECT method of measuring the amount of mass at the Antarctic (ice, land, ocean). The altimetry data are actually measuring the HEIGHT of the ice there, and inferring the mass (it's not a bad method, but it is an inferred rather than a direct measurement).
So, EITHER, the gravimetric data are more inaccurate than previously assumed (that study was also this year, so it's 'new' data), OR the altimetry data are potentially being 'fooled' by variations in the density of the ice and snow. Think of it like a corked baseball bat. From the outside, you cannot tell the difference between a regular bat and a corked one, if the end is sufficiently masked or painted. BUT, if you WEIGH them both, you will find the corked one is lighter, because it is filled with less dense material.
It will be interesting to see how these to data sets are reconciled among glaciologists. In the GRACE (gravimetric data) paper from April of this year, the authors even point out the 'corked bat' or volume vs mass notion specifically:
The Princeton study differs from existing approaches to measuring Antarctic ice loss in that it derives from the only satellite data that measure the mass of ice rather than its volume, which is more typical, Simons explained. He and Harig included monthly data from GRACE, or the Gravity Recovery and Climate Experiment, a dual-satellite joint mission between NASA and the German Aerospace Center. GRACE measures gravity changes to determine the time-variable behavior of various components in the Earth's mass system such as ocean currents, earthquake-induced changes and melting ice. Launched in 2002, the GRACE satellites are expected to be retired by 2016 with the first of two anticipated replacement missions scheduled for 2017.
While the volume of an ice sheet — or how much space it takes up — is also crucial information, it can change without affecting the amount of ice that is present, Simons explained. Snow and ice, for instance, compact under their own weight so that to the lasers that are bounced off the ice's surface to determine volume, there appears to be a reduction in the amount of ice, Simons said. Mass or weight, on the other hand, changes when ice is actually redistributed and lost.
Simons equated the difference between measuring ice volume and mass to a person weighing himself by only looking in the mirror instead of standing on a scale.
"You shouldn't only look at the ice volume — you should also weigh it to find the mass changes," Simons said. "But there isn't going to be a whole lot of research of this type coming up because the GRACE satellites are on their last legs. This could be the last statement of this kind on these kinds of data for a long time. There may be a significant data gap during which the only monitoring available will not be by 'weighing' but by 'looking' via laser or radar altimetry, photogrammetry or field studies."
While the volume of an ice sheet — or how much space it takes up — is also crucial information, it can change without affecting the amount of ice that is present, Simons explained. Snow and ice, for instance, compact under their own weight so that to the lasers that are bounced off the ice's surface to determine volume, there appears to be a reduction in the amount of ice, Simons said. Mass or weight, on the other hand, changes when ice is actually redistributed and lost.
Simons equated the difference between measuring ice volume and mass to a person weighing himself by only looking in the mirror instead of standing on a scale.
"You shouldn't only look at the ice volume — you should also weigh it to find the mass changes," Simons said. "But there isn't going to be a whole lot of research of this type coming up because the GRACE satellites are on their last legs. This could be the last statement of this kind on these kinds of data for a long time. There may be a significant data gap during which the only monitoring available will not be by 'weighing' but by 'looking' via laser or radar altimetry, photogrammetry or field studies."
Also worth noting...the GRACE satellites which took the gravimetric data have done so since 2002, and are due to retire in 2016; replacements are set to be launched in 2017, but I'm not sure if that will occur if Congress cuts NASA budgets for climate science.....in other words, there is potential that we could lose the MOST accurate measurement of Antarctic land ice gain or loss....
